radiochromic ﬁlm dosimetry: recommendations of …lcr.uerj.br/manual_abfm/radiochromic film...

Radiochromic film dosimetry: Recommendations of AAPM RadiationTherapy Committee Task Group 55

Azam Niroomand-Rad, ChairDepartment of Radiation Medicine, Georgetown University Medical Center, Washington, DC

Charles Robert BlackwellTherapeutic Radiology, Mayo Clinic, Rochester, Minnesota

Bert M. CourseyNational Institute of Standards and Technology, Gaithersburg, Maryland

Kenneth P. GallDepartment of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, Texas

James M. GalvinDepartment of Radiation Oncology, Thomas Jefferson University, Philadelphia, Pennsylvania

William L. McLaughlinNational Institute of Standards and Technology, Gaithersburg, Maryland

Ali S. MeigooniDepartment of Radiation Medicine, University of Kentucky, Lexington, Kentucky

Ravinder NathDepartment of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut

James E. RodgersDepartment of Radiation Medicine, Georgetown University Medical Center, Washington, DC

Christopher G. SoaresNational Institute of Standards and Technology, Gaithersburg, Maryland

~Received 10 June 1998; accepted for publication 18 August 1998!

Recommendations of the American Association of Physicists in Medicine~AAPM! for the radio-chromic film dosimetry are presented. These guidelines were prepared by a task group of theAAPM Radiation Therapy Committee and have been reviewed and approved by the AAPM ScienceCouncil. © 1998 American Association of Physicists in Medicine.@S0094-2405~98!00211-9#

Key words: radiochromic films, film dosimetry, film scanners

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TABLE OF CONTENTS

I. INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . .2094II. HISTORICAL BACKGROUND AND

CHEMICAL MAKEUP. . . . . . . . . . . . . . . . . . . . . .2094A. Historical background of radiochromic

dosimeters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2094B. Physical-chemical behavior of radiochromic

dosimeters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2095C. Radiochromic films. . . . . . . . . . . . . . . . . . . . . . .2095

III. RADIOCHROMIC FILM DOSIMETRY. . . . . . . . 2096A. Radiochromic film dosimeters. . . . . . . . . . . . . . . 2096B. Structure and atomic constituents/tissue

equivalence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2097C. Irradiated and unirradiated absorption spectra. . 2D. Processing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2097E. Postirradiation color stability with time. . . . . . . 2098F. Response to polarized light. . . . . . . . . . . . . . . . . 2098G. Response and energy dependence. . . . . . . . . . . . 2099H. Dose fractionation. . . . . . . . . . . . . . . . . . . . . . . .2099I. Dose rate independence. . . . . . . . . . . . . . . . . . . . 2099J. Environmental stability.. . . . . . . . . . . . . . . . . . . 2100

1. Temperature and relative humidity during

2093 Med. Phys. 25 „11…, November 1998 0094-2405/98/25 „

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storage and readout. . . . . . . . . . . . . . . . . . . . 21002. Temperature during irradiation and

postirradiation. . . . . . . . . . . . . . . . . . . . . . . . .21003. Ultraviolet light. . . . . . . . . . . . . . . . . . . . . . .2101

K. Image resolution. . . . . . . . . . . . . . . . . . . . . . . . . .2101L. Film uniformity. . . . . . . . . . . . . . . . . . . . . . . . . .2101M. Film calibration and sensitivity. .. . . . . . . . . . . . 2103N. Dose calculation using a double-exposure

technique. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2103O. Shipping and handling. . . . . . . . . . . . . . . . . . . . .2104P. Summary characteristics of radiochromic films.. 21Q. Summary procedures for radiochromic film

dosimetry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2104IV. SCANNING DENSITOMETER SYSTEMS. . . . . 2105

A. Techniques of two-dimensional dataacquisition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2105

B. Characteristics of light sources. . . . . . . . . . . . . . 2106C. Characteristics of light detectors. . . . . . . . . . . . . 2106D. System response spatial resolution linearity. . . . 2107E. Spatial resolution. . . . . . . . . . . . . . . . . . . . . . . . .2107F. Positional accuracy. . . . . . . . . . . . . . . . . . . . . . . .2107G. Acquisition time. . . . . . . . . . . . . . . . . . . . . . . . . .2108H. Control software. . . . . . . . . . . . . . . . . . . . . . . . . .2108I. Environmental factors. . . . . . . . . . . . . . . . . . . . .2108

209311…/2093/23/$15.00 © 1998 Am. Assoc. Phys. Med.

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J. Specifications of some scanning densitometersystems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2108

V. MEDICAL APPLICATIONS OFRADIOCHROMIC FILMS. . . . . . . . . . . . . . . . . . . . 2108A. Ophthalmic applicator dosimetry. . . . . . . . . . . . . 2108B. Brachytherapy dosimetry. . . . . . . . . . . . . . . . . . . 2109C. Interface dosimetry. . . . . . . . . . . . . . . . . . . . . . . .2109D. Stereotactic radiosurgery dosimetry. . . . . . . . . . . 2109E. Dosimetry in the penumbra region of

I. INTRODUCTION

In radiation dosimetry there are numerous problems assated with the measurement of isodose curves and depth-distributions in high-gradient regions of beams using cventional measuring systems such as ionization chambsemiconductors, thermoluminescent detectors~TLDs!, andradiographic films. Ionization chambers and semiconducdo not provide sufficient spatial resolution for many trement planning needs. Thermoluminescent dosimeters, ewith small dimensions, are cumbersome and time consumwhen one- or two-dimensional dose distributions arequired. Dosimetric data cannot be stored for archival pposes by using conventional TLD readout procedures.evaluation of an ionizing photon beam is difficult by usinsilver-halide radiographic film, because of large differencin sensitivity to photon energies in the 10–200 keV regioeven though its relatively high spatial resolution offersadvantage over most other radiation measuring systemsergy absorption and transfer properties of radiographic fido not match those of biological tissues. Radiographic filalso have the disadvantages of being sensitive to roomand requiring wet chemical processing.

These difficulties have resulted in a search for a radiadosimeter with high spatial resolution which does not requa special developmental procedure and gives permanensolute values of absorbed dose with an acceptable accuand precision and ease of handling and data analysis. Sof these features have been achieved with the introductioradiochromic dosimeters. These dosimeters, with very hspatial resolution and relatively low spectral sensitivvariation, are insensitive to visible light, thus offering easehandling and preparation in room light. Radiochromic dsimeters color directly and do not require chemicprocessing—a color change~colorless to blue, red, greenetc.! indicates exposure to radiation. Image formation occas a dye-forming or a polymerization process, in whichergy is transferred from an energetic photon or particle toreceptive part of the leuko-dye or colorless photomonommolecule, initiating color formation through chemicchanges.

Since 1965, detailed studies have been performedMcLaughlinet al.1,2 and other investigators to determine tdosimetric properties of various forms of radiochromic mdia. Much of the effort has been carried out at the U.S. Ntional Institute of Standards and Technology~formerly theNational Bureau of Standards!, initially with support fromthe Division of Isotopes Development, U.S. Atomic Ener

Medical Physics, Vol. 25, No. 11, November 1998

radiotherapy beams. . . . . . . . . . . . . . . . . . . . . . . .2109F. Hot particle dosimetry. . . . . . . . . . . . . . . . . . . . .2111G. Dosimetry for radiation inactivation and target

size analysis. .. . . . . . . . . . . . . . . . . . . . . . . . . . .2111H. Intravascular brachytherapy dosimetry. . . . . . . . 2112I. Proton dosimetry. . . . . . . . . . . . . . . . . . . . . . . . .2112

VI. PROCEDURE SUMMARY FORRADIOCHROMIC FILM DOSIMETRY. . . . . . . . 2112

VII. FUTURE DIRECTIONS. . . . . . . . . . . . . . . . . . . . 2113

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Commission, and with the assistance of the inventor oftraviolet sensitive systems, L. Chalkley.3 With the recent im-provement in the accuracy and precision of film manufacting, as well as the ruggedness and ease of use, radiochrdosimeters have become increasingly popular in medicalnonmedical applications. Over the past several years thesimetric properties of radiochromic dosimeters have bevaluated by many investigators and extensive literaturevarious aspects of radiochromic dosimetry has appearedpresent, various radiochromic dosimeters in the form of tfilms, thick films, gels, liquid solutions, and liquid-corwaveguide, are used for routine dosimetry of ionizing radtion over a wide range of absorbed doses (1022– 106 Gy)and absorbed dose rates~up to '1012 Gy s21).4 In recentyears, various radiochromic dosimeters have also beenfor nonclinical applications such as blood irradiation,5 radia-tion processing,6 and reference standard.7

At this time, there are no comprehensive guidelines onuse and calibration of radiochromic films and the densitoetry systems for clinical use. This report has been prepaby Task Group 55 of the Radiation Therapy Committeethe American Association of Physicists in Medicine, AAPMprimarily to fill the needs of a hospital physicist in utilizinradiochromic films for medical applications. The develoment of radiochromic dosimeters and the methodologytheir applications is an ongoing process. This report inteto reflect on the current state of scientific understandingtechnical methodology in clinical radiochromic dosimetrAs such, it is not final but is offered as an up-to-date aidthe clinical physicist. The scope of this report has been lited to:

~1! characteristics of available radiochromic films,~2! procedures for using radiochromic films for dosimetry~3! characteristics of scanning systems and densitomete~4! medical applications of radiochromic detectors, and~5! future directions.

Tasks related to the dosimetry of other forms of radiochmic detectors, such as gels, are separate subjects and apart of this task group report.

II. HISTORICAL BACKGROUND AND CHEMICALMAKEUP

A. Historical background of radiochromic dosimeters

Radiochromic effects involve the direct coloration ofmaterial by the absorption of energetic radiation, without

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quiring latent chemical, optical, or thermal developmentamplification.2,8–13 The radiochromic process, describedthis section, involves the production of immediate permancolored images of a radiation exposure pattern in a sowith or without ‘‘fixing’’ of the sensor medium against further change. Typical films, protected from further irradtions, can serve as archival radiographic imaging and dstorage media.

One of the first commercially important direct-imaginreactions involved papers and gels impregnated with posium dichromate, which was known to undergo photoredtion. This led to daguerreotype, collotype, photogravure,photolithographic prints in the mid-1800 s. This processthe inverse of radiochromism, in that the brownish colorleft in the unreduced portions of the image. A very earadiochromic process, first demonstrated in 1826 by Niep8

involved an unsaturated hydrocarbon polymeric mixtubased on bitumen that cross links upon irradiation, leavinlight-scattering pattern. Many radiation cross-linking orgasystems have subsequently been used for radiograimaging.8–11

One type of organic free-radical imaging medium ccombine photopolymerization with leuco dyes that producolor upon irradiation. Typical of such processes is the ping of free radicals to form radiation cross-linked carbochain materials, resulting in covalently bonded growichains. Other direct-imaging effects include radiatioinduced vesicular films giving light-scattering properties14

and the radiation-induced changes in the hardness of pmeric microcapsules containing diffusible dyes, inks, apigments that are released mechanically.15,16

Some radiochromic organic image-forming systemsvolve cis–trans isomeric conversions, or dissociations resuing in enolic, ketonic, and anilic bonds and other molecurearrangements. Such tautomerizations lead to doubonded coloration of spiropyrans, anils, organic acids, sbenes, and other polycyclic compounds.10,17

Colorless transparent radiochromic thin films giving pmanently colored images have been widely used for 30 yas high-dose radiation dosimeters (104– 106 Gy).11,12,18

These are mainly hydrophobic substituted triphenylmethleucocyanides, which upon irradiation undergo heterolybond scission of the nitrile group to form highly colored dsalts in solid polymeric solution. The host material for sufilms is generally nylon, vinyl, or styrene-based polymThey have also been used to register high-resolution, hcontrast radiation images and to map radiation dose distrtions across material interfaces.19 This kind of radiochromicsystem is not sensitive enough to be used for clinicalradiological applications.

Some triphenyl tetrazolium chloride~TTC! salts can beused as direct-imaging biological stains for botanical spemens and for characterizing normal and malignant mamlian tissues.20–22These salts are colorless in aqueous solutbut upon irradiation are reduced to the highly colored,soluble formazans. For radiographic imaging in hydrocloids and other aqueous gels, and for mapping ionizingdiation dose distribution directly in animal tissue


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hydrophilic TTC salts23,24 and triphenylmethane leucocyanides~e.g., formyl violet nitrile!25 have been used.

Recently, another form of radiochromic film basedpolydiacetylene has been introduced for mediapplications.26–32 These films were previously supplied itwo types, GafChromic DM-1260~also known as HD-810!—see Sec. III for nomenclature designation—asingle-layer GafChromic MD-55 for the absorbed doranges 50–2500 and 10–100 Gy, respectively.28,33,34 @Thesingle-layer GafChromic film will be designated as ‘‘MD55-1’’ in this report. ~See Sec. III!.# A new double-layerGafChromic MD-55 film has now replaced the other two fmedical applications~useful dose range 3–100 Gy!.35,36

@This currently available double-layer GafChromic film wbe designated as ‘‘MD-55-2’’ in this report.~See Sec. III!.#Each of these film types is colorless before irradiation, csisting of a thin, active microcrystalline monomeric dispesion coated on a flexible polyester film base. It turns progrsively blue upon exposure to ionizing radiation. Thradiochromic radiation chemical mechanism is a relativslow first-order (k>103 s21) solid-state topochemical polymerization reaction initiated by irradiation, resulting in hmogeneous, planar polyconjugation along the carbon-chbackbone.33,34

The characteristics of these most relevant and sensradiochromic films, i.e., MD-55-1 and MD-55-2, are givenSec. III.

B. Physical-chemical behavior of radiochromicdosimeters

McLaughlin et al.35 have studied the radiochromic filmMD-55-1 by pulse radiolysis and flash photolysis, in termsthe kinetics of their response to ionizing radiation and ultviolet light.33,34 The radiochromic reaction is a solid-stapolymerization, whereby the films turn deep blue proportioately to radiation dose, due to progressive 1,4-transadditionswhich lead to colored polyconjugated, ladderlike polymchains. The pulsed-electron-induced propagation of polymization has an observed first-order rate constant on the oof 103 s21, depending on the irradiation temperature~activa-tion energy'50 kJ mol21!. The UV-induced polymerizationis faster by about one order of magnitude (kobs

51.53104 s21). In the case of the electron beam effect, tradiation-induced absorption spectrum exhibits a muslower blueshift of the primary absorption band (lmax56752660 nm) on the 1023– 1011 s time scale. This effect isattributed to crystalline strain rearrangements of the stacpolymer strand units.

C. Radiochromic films

The new proprietary radiochromic films MD-55-2 consof double-layer radiochromic sensors dispersion coatedboth sides of a polyester base34,38 ~see Sec. III A!. The col-orless, transparent film responds to ultraviolet light andionizing radiation by turning blue, with two nominal absortion bands (lmax;670 and 610 nm! which depend on theabsorbed dose, temperature during irradiation, as wel

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postirradiation reading time. The radiation-induced cochange is formed directly without thermal, optical, or chemcal development and the original blue image is stable at tperatures up to about 60 °C, above which the color ofimage changes abruptly from blue to red. This film has vlittle dependence on relative humidity during irradiation, bthere is a marked temperature dependence, the degrewhich varies with radiation dose and temperature level.37–39

For example, at a dose of 10 Gy, the new radiochromic fi~GafChromic MD-55-2!, read at a wavelength of 670 nmshows a 5% increase in response when the irradiation tperature is increased from 20 to 40 °C.35 At higher tempera-tures~between 40 and 50 °C!, the response increases due torise in irradiation temperature by;1.6% per °C. Theg-rayand electron response shows negligible dose-dependence.38 When the films are irradiated with photonsdose rates between 1.0 and 30 Gy/min or with electbeams at an average dose rate of'106 Gy/min, the valuesof radiation-induced absorbance increase per unit dose ato within the specified uncertainty of the dosimetric respo~65% at 95% confidence level!.38 Response curves for MD55-2 are presented in Fig. 1~a!.35 The radiation-induced absorption spectra, shown in Fig. 1~b!, are similar to thoseobtained for earlier versions~e.g., DM-1260! of thesefilms.33 All spectrophotometric measurements given hwere taken at 2261 °C. The estimated combined uncertaities for these measurements are65% at two standarddeviations.38 Higher dose levels can be measured by jucious selection of spectrophotometric wavelength. It hbeen demonstrated that the earlier DM-1260 film providvery high spatial resolution images. For ionizing photons aelectrons in the energy region 0.1–10 MeV, the sensor silates the radiation absorption properties of water and musin terms of ratios of photon mass energy-absorption coecients and electron mass collision stopping powers, wit62%.35,40,41 However, experimental studies of the depedence of the film response on photon energy show thaterms of absorbed dose in water, the response to photonthe 0.03–0.04 MeV range is about 60% of that at phoenergies.0.1 MeV.35 ~See Sec. III.!

Two radiochromic systems that have been developedradiographic imaging and dosimetry at absorbed dogreater than those used for radiation therapy are thin ficontaining either amino-triphenylmethane leucodyes or tezolium salts as the colorless radiation sensitive ingrediewhich are changed to deep colors upon irradiation. Histordetails and the results of radiation chemical kinetics studof these systems can be found in a series of publicationMcLaughlin et al.2,11–13,18,35,42–47

III. RADIOCHROMIC FILM DOSIMETRY

A. Radiochromic film dosimeters

The chemistry and dosimetry of radiochromic dosimethave evolved very rapidly over the past few years. Variotypes of radiochromic films~such as HD-810, DM-1260DM-100, MD-55, and NMD-55!, referred to as GafChromicfilms, have been identified by the catalog number of a s


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plier, Nuclear Associates. The sensitivity and, possibly,dependence on environmental parameters, differ from typtype. Over the past few years, the sensitive structure ofGafChromic films has been changed, more than once, wout the changes being known to the users. In some instathe manufacturer’s film designation remained unchaneven though its structure was altered. To avoid confusand to be able to compare results it is useful to recognizemanufacturer’s stated lot number for a given film type.

At the time of the writing of this report the two commecially available radiochromic films for medical applicationare:

~1! GafChromic HD-810 film~formerly this film was sup-plied as a GafChromic DM-1260 and was only availabin 12.5 cm315 m!: This film can be purchased from thmanufacturer@International Specialty Products~ISP!,Wayne, NJ# and is available in 20 cm325 cm clearsheets.

~2! Double-layer GafChromic MD-55-2 film~in this report,the double-layer GafChromic films are designatedMD-55-2!: This film can be purchased from the manfacturer@International Specialty Products~ISP!, Wayne,NJ# as well as other vendor~s! ~Nuclear Associates, CarlePlace, NY! and is designated as model No. 37-041.addition to model numbers, lot numbers may proviuseful information. From September 1994 to Decem1995, the manufacturing lot number for this film wa940818. In January 1996, the lot number for this fiwas changed to 941206. More recently, since 1997,film has been manufactured with the following lot numbers: 970116, 37051, 37175, and 38055. This filmcurrently available in 12.5 cm312.5 cm clear sheetsSome publications have referred to this~new! double-layer GafChromic film as NMD-55 ~viz. ‘‘new’’MD-55!. @Before September 1994, a less sensitsingle-layer GafChromic film also designated as MD-~model No. 37-041!, was available from Nuclear Associates. The manufacturing lot number for this film w920813. In this report this single-layer film is designatas MD-55-1.#

Radiochromic MD-55-2 films are suitable for dose mesurements in the range of 3–100 Gy; whereas HD-810 fiare mainly used for dose mapping in the range of 50–2Gy. The present physical dimensions of these films limtheir clinical application for large-field dosimetry of lineaaccelerators.

Although the production of some of these films has bediscontinued, investigators may have purchased a laquantity of HD-810~formerly DM-1260 rolls! and MD-55-1films which are still in use in their department. Specific iformation for all types of radiochromic dosimeters is navailable. Therefore, data related to these three types odiochromic films are presented here. Radiochromic doseters, in general, have many advantageous characteristiwell as some limitations which are discussed in the followisections.28,35,37,47A summary of these characteristics, as th

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apply to various types of radiochromic films, is providedSec. III P.

B. Structure and atomic constituents/tissueequivalence

The HD-810 dosimetry film has a nominal 7-mm-thickradiation sensitive layer on a 100mm polyester base. TheMD-55-1 and MD-55-2 is a film composed of a~single ordouble! layer~s! of highly uniform transparent coating, sensitive to ionizing radiation, on~one or two! piece~s! of apolyester base. See Table I and Fig. 2 for details.48 The thinradiosensitive layer is made of colorless organic microcrtals of a radiation-sensitive monomer uniformly disperseda gelatin binder.26–28,33–35The sensor layer of these films haatomic constituents with various proportions~Fig. 2!.28 Theradiation absorption properties of radiochromic dosimetcan also be adjusted by changing film composition. Thesimeter materials can be made to simulate the materiainterest undergoing irradiation~e.g., tissue, bone, various insulating materials!.4,49 The effective Z of these films iswithin the range 6.0–6.5. The energy dependence ofresponse to electrons, as well as the range of electrons indosimeter sensor and its substrate~polyester!, has been de-termined by computation of mass collision stopping powand continuous-slowing-down approximation rangeselectrons.28 The energy dependence of this film to photenergies has been calculated by considering mass attenucoefficients and mass energy absorption coefficients.28 Thesensor material is similar in its electron stopping powerswater and muscle.28 It is also similar to water and muscle iterms of mass energy-absorption coefficients for photonenergies greater than 100 keV.28,38 For the photon energyrange of 0.1–1.33 MeV, and for secondary electrons fr0.1 to 1.0 MeV, photon mass energy absorption coefficieand electron mass collision stopping powers, for the senare within 2% of water and skeletal muscle.35

C. Irradiated and unirradiated absorption spectra

The radiosensitive layer~s! in GafChromic film containmicrocrystals of a monomer. As described in Sec. II,radiosensitive layer undergoes partial polymerization whirradiated with ionizing radiation, such that the blue colorthe polymer becomes progressively darker as the dincreases.34 Figure 3~A! shows the optical absorption spetrum of MD-55-2 from 600 to 700 nm, before and afterdose of 6 Gy.50 As shown a small shift in peak positiooccurs with dose@675 nm at 0 Gy~unirradiated film! to 676nm at 6 Gy#. Similarly, for the weaker peak, there is a smshift from 617 nm for 0 Gy to 618 nm at 6 Gy.50 Figure 3~B!shows the spectrum of an unirradiated film from 700 to 7nm taken with a bandpass of 1.0 nm.50 The interferencefringes looked about the same with a bandpass of 0.25but were ten times smaller when a bandpass of 3.5 nmused. Using a bandpass of 3.5 nm, the optical density~OD!,measured at 676 nm for a dose of 6 Gy, would differ0.2% at an adjacent peak and valley of the fringes.50 Thespectrum of unirradiated film@Fig. 3~A!# shows the presenc


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of some polymer plus an ‘‘underlying absorption.’’ Assuming that the ‘‘underlying absorption’’ is featureless and uchanged by irradiation, Klassenet al.50 conclude that in Fig.3~A!, it accounts for 0.20 OD units between 618 and 676 nThey argue that some of the apparent absorption is actualoss of light due to reflection, not absorption.50

D. Processing

Exposure to ionizing radiation results in a change fromcolorless state to shades of blue due to a solid state polymization reaction.28,33,34 No physical, chemical, or thermaprocessing is required to bring out this color and relativlittle change in color density occurs following the initial 24after the exposure.28,39The increase in color of radiochromifilms is usually measured at a narrow spectral wavelen

FIG. 1. ~a! Increase of absorbance at three wavelengths as a function of60Cog-radiation dose, for MD-55-2 radiochromic film;~b! radiation-induced ab-sorption spectra of MD-55-2 radiochromic film~Ref. 35!.


Medical Physics, Vo

TABLE I. Structure/dimensions of radiochromic films.

Film type HD-810~DM-1260! MD-55-1 MD-55-2Nuclear Assoc. No. — 37-041 37-041Standard size 20320 cm2 12.5312.5 cm2 12.5312.5 cm2

~12.5 cm315 m roll!Nominal thickness~mm! 107 ~Fig. 2! 82 ~Fig. 2! 278 ~Fig. 2!Sensitive layer~s! ~mm! 761 1561 3061Base material~mm! 99 67 159

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E. Postirradiation color stability with time

Nearly full color development of all radiochromic formulations is very rapid, generally occurring in a femilliseconds.33,34 However, several radiation chemical efects in plastics systems require some time, minutes and ehours, after irradiation to reach chemical completion. Thefore, with some dosimeters, a slow spontaneous developmeffect occurs after irradiation to different degrees dependon whether the irradiation time was long or short.51 Mostplastic dosimeters tend to be unstable in their responseing the storage period between irradiation and analysis.52–54

The color formation in the irradiated radiochromic filtypes ~e.g., MD-55-1 and MD-55-2! is not complete at theend of the irradiation. It continues at an ever decreasrate.28,33,34,50,55Absorbancies of such films were measured400 nm at different times after irradiation, showing a cotinuous rise in relative absorbance.28,56 During the first 24 hafter the irradiation, the absorbance can increase by u16%, with only a slight rise~4%! thereafter, for up to aboutwo weeks.28 The time effect was found to depend on tabsorbed dose.28,50No appreciable postirradiation changesabsorbance, at 400 nm, of the film occurs over the pefrom 40 to 165 days. Color stability is enhanced for absbance readings made at either of the two main absorppeaks~nominal 610 and 670 nm!.28 It has also been notethat the greatest increase in absorbance occurs at higherage temperatures, near 40°C.27 Such an effect may requirattention under typical storage conditions. Generally, at ctain wavelengths of the main absorption band~e.g., nominal670 nm!, the radiation effect is relatively stable following thfirst 4 h after irradiation.57 To minimize dosimetric variationsdue to the instability effect, spectrophotometric or densmetric readings should be made consistently at a cerwavelength.34,35

F. Response to polarized light

The analyzing light in most spectrophotometers and dsitometers, whether the light source is a lamp or a laselinearly polarized to some extent. Klassenet al.50 have ex-tensively investigated the response of various layers of M55-2 film to polarized light. Scanning electron micrograp

l. 25, No. 11, November 1998

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suggest that the microcrystals in the radiosensitive layerMD-55-2 have a preferred orientation, i.e., they are lyiflat. As explained by Klassenet al.,50 if in addition, themonomers in the microcrystals have a preferred orientain the same plane of the film, this could lead to dichroissuch that the OD would vary with the plane of polarizati

FIG. 2. Diagram of radiochromic~GafChromic! film structure/dimension.

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of the analyzing light and, hence, would change as thewas rotated or turned back to front in the spectrophotomeKlassenet al.60 found that the outer polyethylene terepthalale ~PTP! layer of MD-55-2 had little effect on the polarization of the analyzing light, but the middle layestrongly rotated the plane of the light in the fashion of a 1wave plate. The result is that the plane of polarization oflight is different for the two sensitive layers. They concludthat the measured OD of MD-55-2~as presently fabricated!may change substantially due to the polarization of the alyzing light if the film is rotated or turned back to front in thspectrophotometer.50 Therefore film orientation and alignment should be consistent with the ones used for calibrat

G. Response and energy dependence

Uniformity of the coating and reproducibility of individual polydiacetylene film sample measurements have breported by Saylor and McLaughlin.27 The HD-810 film re-sponses per unit absorbed dose to water~or simply film re-sponses! in the dose range 50–2500 Gy were studied usvisible spectrophotometry, color photometry, densitomeand scanning densitometry. The film was found to be esstially insensitive to light at wavelengths above 300 nm; hoever, it is sensitive to ultraviolet light at lower wavelengthIt has been suggested that the film be stored in the dartemperatures below 25 °C and relative humidities bel50% to optimize the useful life of the film. In addition, aoptical densities should be measured at the same temper~to within 62 °C! and postirradiation delay~to within 62 h!to obtain optimum reproducibility, as absorption spectrupeaks shift with temperature and time.28 The climate inside atypical modern medical facility easily meets these tempeture and humidity requirements.

The first available film~DM-1260! was not sensitiveenough to measure typical clinical doses, and it requidoses on the order of 50 Gy or greater for62% precision.The more sensitive MD-55-2 film, with double sensitiv

FIG. 3. ~A! The optical absorption spectrum of unirradiated GafChromMD-55-2 ~lower spectrum! and GafChromic MD-55-2 several weeks afterdose of about 6 Gy~upper spectrum!. The bandpass used was 3.5 nm. Souseful wavelengths are indicated.~B! The spectrum of unirradiatedGafChromic MD-55-2 taken using a bandpass of 1 nm and displayedhigher sensitivity than in~A! in order to demonstrate the periodic fluctutions due to interference fringes~Ref. 50!.


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coatings~nominal 30mm!, has become available for measuing doses as low as about 3 Gy with similar precision.35

Several investigators have studied the energy dependof the radiochromic film response.35,38,39 Muench et al.39

have compared the variation of the low-sensitivity radiochmic film HD-810 ~formerly DM-1260! response with thoseof LiF TLD chips ~Fig. 4! in the effective photon energyrange of 20–1710 keV. The HD-810 film response is oserved to decrease by about 30% as effective photon endecreases from 1710 keV~4 MV x rays! to 28 keV~60 kV xrays, 2 mm Al filter!. This variation is similar but in theopposite direction to that of LiF TLD chips. In contrast, ovthis range of photon energies, the sensitivity of verificatisilver halide film ~Kodak X-Omat V film! increases by980%.39

Chiu-Tsao et al.58 have measured the variation of thMD-55-1 film response with energy for the dosimetrybrachytherapy sources~Fig. 5!. Their results indicated thatfor these films, the sensitivity is about 40% lower for125Ithan 60Co. The experimental studies of McLaughlinet al.35

with photon beams show a response of MD-55-2 to be ab40% lower for photons of 20–40 keV than with137Cs or60Co gamma radiation when absorbed dose in water is msured~see Fig. 6!. Meigooniet al.59 have compared the characteristics of MD-55-2 with those of MD-55-1. They havshown MD-55-2 to be approximately 40% more sensitthan MD-55-1 for megavoltage photon beams. Sayeget al.60

have suggested that the lower response of the radiochrofilm for energies lower than 100 keV is due to the largcarbon content in the film relative to that in soft tissue. Tmeasurement precision is limited primarily by the uniformof the film thickness and the instrumentation used for dentometry. Photometric analysis, with three replicates per dpoint, gives a reproducibility~62 SD! of well under 5%.28

With care reproducibility of 1% is achievable.50 The depen-dence of the absorbance spectrum of MD-55-1 film updose has been documented~Fig. 7!, where doses were delivered using90Sr190Y beta particles at the surface of a cabrated ophthalmic applicator.30,61

H. Dose fractionation

The possible effect of dose fractionation for HD-810 filhas been studied in two ways. In the first, the irradiation winterrupted four times for 12 min before being continued.the second, the irradiation was interrupted for 24 h befbeing continued. The total absorbed dose in the first case5 kGy so that each fraction was 1 kGy. In the second cathe absorbed dose range was from 5 to 35 kGy. In both cathe absorbance values of the unfractionated and the fracated dosimeters were within 1% for HD-810 film.56 Dosefractionation effect information, for the MD-55-1 or MD55-2 film, was not available at the time of this report.

I. Dose rate independence

The MD-55-1 film was tested for dose rate dependeusing calibrated60Co sources with dose rates of 0.020, 271.0, and 198 Gy/min, for total doses up to 1.5 kGy. Ana

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sis was performed at wavelengths near the maximum oftwo peaks~'670 and'610 nm! of the absorption spectrum~see Fig. 7!. Results show that, within an uncertainty of aproximately 5%~6 one SD!, there is no rate dependence27

A more recent study by McLaughlin35 using the double-layeMD-55-2 film, irradiated at three absorbed doses, 20, 40,60 Gy in the absorbed dose rate range 0.08–80 Gy/mshows no rate dependence of response within the samecertainty as that of MD-55-1, except at the highest dose oGy. At this relatively high dose there is about a 10% grearesponse at the lowest dose rate than at the highest dos~see Fig. 8!. In general, radiochromic film is independentdose rate effects at the clinically relevant dose rates of 2Gy/min.

J. Environmental stability

The responses of radiochromic dosimeters are usuallyfluenced by temperature and relative humidity and in socases by ambient light and gases. Since conditions madifferent between calibration and practical use, variationsresponse with the surrounding conditions must be demined and corrected. In the following sections, outlinespresently known effects on the response of radiochromicto temperature, humidity, and ambient light conditionsdescribed.28,37,59,62

1. Temperature and relative humidity duringstorage and readout

In general, a 24 h period between irradiation and readhas been suggested for the radiochromic films until relastability is achieved.28 However, the relative change of ODdue to the postirradiation coloration after irradiation mayinfluenced by both temperature and relative humidity durpostirradiation storage. The effect of humidity on HD-8film during irradiation and storage has been reported toless than 62% over the relative humidity rang6%–94%.27,37 The effect of temperature differences durinspectrophotometry of the same film shows a shift of thesorption bands to shorter wavelengths and an increase inabsorption band amplitudes with increase in readtemperature.28,50

2. Temperature during irradiation andpostirradiation

McLaughlin et al.28,35,54,63–65have studied the irradiationtemperature effects on most current and proposed solid-dosimetry materials applicable to high dose measuremeThey found the dye cyanide radiochromic materials to beleast affected by temperature variation.64 However, tempera-ture dependence may contribute large errors to the dose rings for many of the high-dose dosimeters, particularly if tcalibration is performed under conditions different frothose in practical applications. By calibrating the respoprecisely under the conditions of use~corresponding frac-tionation of dose, elevated temperatures, radiation time, e!,these errors can be minimized.


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There is a marked dependence of the response of rachromic ~polydiacetylene coated! films on temperature during irradiation and postirradiation.65 This dependence variewith dose level as well as the wavelength of analysis.28,35

Figure 9 shows the temperature dependence of MD-55-1MD-55-2 films during irradiation with gamma rays at a doof 40 Gy, measured at four different wavelengths, for teperatures in the range 10–50 °C.35 Relative sensitivity is of-ten expressed as the value of net absorbance per unisorbed dose, relative to that when the irradiation was mad20 °C. As irradiation temperature reaches'50 °C, in mostcases, there is an erratic variation in relative sensitivwhich suggests that this dosimeter should not be used atelevated temperatures. The effect of even greater tempture, .60 °C, on the exposed films results in the blue dchanging to red.34 Prolonged exposure of the unexposed fito temperature.60 °C may cause a significant changesensitivity.28 The postirradiation temperature dependencebeen described in detail by Reinsteinet al.65

FIG. 4. Dosimeter sensitivity of HD-810 film as a function of x-ray quali~equivalent photon energy! for LiF TLD chips and radiochromic film~Ref.39!.

FIG. 5. The dose-response curves of MD-55-1 film measured by a ldensitometer~632.8 nm! for three radionuclides. The square, circle, and psymbols are for125I, 137Cs, and60Co, respectively. The dotted and solilines near the symbols indicate the plot for the corresponding function~Ref. 58!.

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FIG. 6. The experimental photon energy dependence~points! of MD-55-2film irradiated to an absorbed dose iwater of 20 Gy byx and gamma radia-tion. The solid curve represents thcalculated ratios of the mass energabsorption coefficients, MD-55-2 filmsensor material-to-water, for photonfrom 10 to 1250 keV, normalized tothe experimental value at 1250 keVThe vertical bars on the experimentapoints represent uncertainty limitsbased on five replicates at each poi~Ref. 45!.

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3. Ultraviolet light

Most radiochromic films are sensitive to ultraviolet radtion, which spontaneously colors the film; they must be ptected from sunlight or continuous white fluorescelights.57,64,65Proper care and handling can eliminate ultravlet exposure. The dosimeter may be stored in an opaquetainer, carton, or envelope; removed from the containerbackground reading taken as needed; and immediatelyfor exposure.28 Qualitative studies of radiochromic film MD55-2 have been shown it to be insensitive to ultraviolet avisible light at wavelengths above 400 nm.57

K. Image resolution

Image resolution of HD-810 dosimetry film with 20 keelectrons in a vacuum has been studied by McLauget al.28 The modulation transfer function was plotted agaithe spatial frequency of test patterns. An 80% responseobserved at 100 cycles/mm and a 50% response atcycles/mm. In addition, a series of line images was recorwith a 0.1-mm-wide electron beam. Resolution in excess1200 lines/mm~600 cycles/mm! was obtained. This is due tthe micrometer size of the sensitive crystals in the film coing.

The radiochromic films can be analyzed with submillimter resolution by using a scanner such as a He–Ne l

FIG. 7. The dependence of the absorbance spectrum of MD-55-1 film onirradiation level. Doses were delivered using90Sr190Y beta particles at thesurface of a calibrated ophthalmic applicator~Ref. 27!.


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scanning densitometer.66 Choosing a laser of appropriatwavelength, high intensity, and low power consumptionimportant. The characteristic 632.8 nm line of a He–Ne lais between the maxima of the two radiation induced absotion bands. For MD-55-2 films, the most sensitive readingmade at the primary radiation induced absorption pe~;670 nm!; therefore a dedicated light emitting-diod~LED!/charged-coupled device~CCD! microdensitometermay be more useful at such wavelengths. While the sparesolution for the polydiacetylene film is known to be betthan 600 cycles/mm, the practical resolving power for doprofiles or isodose contours registered by a scanning ldensitometer using computer software depends on the psize chosen for the measurement routine.38 The characteris-tics of scanning densitometers are discussed in detail inIV.

L. Film uniformity

Radiochromic films are being used as two-dimensio~2D! dosimeters by several investigators in various typesapplications.27,28,33,36–39,47,51,53,56,58,59,63,67,68An ideal 2D do-simeter gives rise to a uniform~constant! response when it isexposed to a uniform irradiation field. For radiochromfilms two aspects of uniformity~or nonuniformity! are ofconcern. The first is the nonuniformity arising fromlocalfluctuations of film response~reading!, qi , with respect to

heFIG. 8. Rate dependence data for MD-55-2 film response when irradiwith 60Co gamma rays to different doses and dose rates, measuredwavelength of 670 nm~Ref. 35!.

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FIG. 9. The temperature dependencethe response of MD-55-1 and MD55-2 films over the temperature rang10–50 °C during irradiation to agamma-ray dose of 40 Gy, read at thindicated optical wavelengths~Ref.35!.

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the mean response,q, in the region of interest. Hence relativ~percent! standard deviation of the film response with respto the mean provides information aboutlocal fluctuations inthe film response. Local fluctuations are small scale andrelated to such variables as the film grain size, spatialsignal resolution of the film scanner, pixel size, pixel depas well as electronic noise. The degree of nonuniformcaused by theselocal fluctuations, i.e., ‘‘spikes,’’ is best assessed by comparison with the mean response and its rel~percentage! standard deviation in the region of interest. Tsecond aspect of nonuniformity isregional variations pro-duced by a systematic problem in the scanner or large snonuniformity in the film emulsion layer~s!. Assessment ofregionalnonuniformity is perhaps best examined graphicabut can be characterized by considering the differences~orratios! of the maximum–minimum responses in the regioninterest, providedlocal fluctuations are omitted. Both aspecof film uniformity, local and regional, are needed to completely characterize it.

Zhu et al.36 have reported 15%regionalnonuniformity ofa particular film batch of MD-55-1. The variations in filmresponse did not appear to have predictable pattern~s!. Mei-gooni et al.59 have also reportedregional nonuniformity upto 15% for the ratio of the maximum–minimum responsesa certain batch of radiochromic film, model MD-55-1. Morover, they have compared theregionalvariations of a single-layer film, MD-55-1, and a double-layer film, MD-55-2along two central orthogonal directions, and have concluthat they both had similar nonuniformity in each directio;4% in longitudinal direction that is parallel to the directioof the coating application, and;15% in the transverse direction that is perpendicular to the direction of the coatiapplication.48,59 ~See Fig. 10! To distinguish these two directions, recently the manufacturer, ISP, clips one corner offilm. The long side of the clipped corner is parallel to tdirection of the coating application.48

Acceptable tolerances for film uniformity vary with applcation. Nevertheless, in a multi-institution investigationthe film uniformity of MD-55-2, the relative~percent! stan-dard deviation of the film response with respect to the mresponse did not exceed63% for high dose range~above.20 Gy! and 65% for low dose range~below ,10 Gy!.69


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Therefore, for most teletherapy applications it may be rsonable to assume that film nonuniformity may not excethese values. Film response should be evaluated using aflat radiation field. Film should be placed on the central ption of a large photon beam~preferably 40340 cm! at thedepth of interest~preferably >5 cm!. The flatness of theradiation beam must be determined by some other dosim~preferably an ionization chamber!.

Furthermore, the results of a multi-institution investigtion indicate that the amplitude oflocal and regional re-sponses varied considerably with different instrumentatioFigure 11 is an example of responses of a MD-55-2 fiexposed to a uniform dose~;20 Gy! and scanned with fivedifferent densitometers at five institutions.69 The film re-sponses, at each institution, are relative to the mean respof the film in the direction of scan. A set of fiduciary marklocated at;1.5 cm from the film edges, are used for idenfication of scan direction and alignment. As shown in F11, the film response is affected not only by the typescanning equipment, but also by other instrumentation ftors such as wavelength of analyzing source, step size,sampling size. A highly coherent light source is more aptgive an interference pattern across a uniform beam thabroad band diffused light source. As evident from Fig. 1high resolution scanners such as the ones used at Getown University, GU, and Washington University, WU, havgiven more noise which should not be attributed to film nouniformity. For further discussion regarding scanning equment and factors affecting dosimetry, readers are referreSec. IV.

Double-exposure technique:If evidence of nonuniformityshould appear, the double-exposure technique is a methoimprove film uniformity to an acceptable tolerance. Zhet al.36 have proposed this technique which is applicableall radiochromic films. In the double-exposure techniquematrix of correction factors is obtained from the relative filresponse exposed to a uniform irradiation field. The sizethis correction matrix depends on the size of the aperturethe densitometer, desired spatial resolution, and mode ofscanning system~linear versus image scanner!. One may usean average of several pixels~e.g., 434 or 10310! to gener-ate the correction matrix. In practice, a layer of film is fir

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marked with at least three fiducial marks and then exposea uniform dose ofD1 ~normally about 15–20 Gy for MD-55-1 film or about 10 Gy for MD-55-2 film!. The mean op-tical density of the film, OD1( i , j )&, in the area of interescan be determined after 24 h. Then the film is exposed tounknown dose ofD2 in the desired irradiation field. The filmis scanned, again after 24 h, and the two images are colated using the three fiducial marks. The optical density frthe first exposure, OD1( i , j ), and the second exposurOD2( i , j ), can be used to obtain a nonuniformity correctnet optical density, ODnet( i , j ), using the following relations:

ODnet~ i , j !5OD2~ i , j !2OD1~ i , j !

f ~ i , j !, ~1!

where

f ~ i , j !5OD1~ i , j !2OD0~ i , j !

^OD1~ i , j !2OD0~ i , j !&, ~2!

and OD0( i , j ), which represents the background~i.e., fog!readings, is the film optical density prior to the first expsure. The double-exposure technique may require writincomputer program for image handling and data analyNote that the double-exposure technique has some limtions. For instance, the accuracy of matching the fidumarks in the two exposures is limited and should be evaated by the user. Therefore, improvement of the film unifmity by the manufacturer is necessary in order to explfurther the full application of radiochromic film.

M. Film calibration and sensitivity

Radiochromic film should be calibrated using a larwell-characterized uniform radiation field. Film should bplaced on the central portion of a large photon beam~such asa 40340 cm! at depth of interest~preferably>5 cm!. Thecharacteristics of the calibration beam should be determby some other dosimeter~such as an ionization chamber!.This would allow direct film calibration in terms of absoludose within the dose range of interest.

The relationship between absorbed dose and film respshould be determined. This relationship can be plotted acurve, often known as a calibration curve. The slope ofcalibration curve decreases as dose increases@Fig. 12~A!#.The calibration curve can provide information for conversiof film response to dose and vice versa.

The relationship between dose and film response canbe tabulated. The change in film response per unit absodose can be represented by a single number for a net opdensity up to 1.0. This number, defined here as film aversensitivity, is the average change in response~i.e., readout!per unit absorbed dose calculated over the lower, most linportion of the calibration curve. This number depends onor more of the following:~1! the wavelength used for readout, ~2! the particular densitometer used for readout,~3! filmbatch, ~4! the delay between irradiation and readout,~5!beam quality of the calibration source, and~6! other factors~such as temperature and humidity! previousely discussedTable II is an example of a film sensitivity calculation fo


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MD-55-2 ~lot No. 941206!, exposed to uniform60Co dosesand scanned after a week delay with a 633 nm LKB dentometer at NIST. The average sensitivity~net OD/Gy! forthis combination, for the dose range 0–30 Gy, from the dabove the line is 0.022360.0007~3.2%!. Figure 12 is a plotof ~A! net OD and~B! net OD per unit absorbed dose mesured two days postirradiation. Figure 12~A! has two fairlylinear portions, one from 0 to 30 Gy, and the other fromto 100 Gy. The average sensitivity for the dose range 30–Gy drops about 15% as compared to the one for the drange 0–30 Gy. This average sensitivity can be usedconversion of film response to dose fortheseconditions andis clearly inappropriate for higher doses or other conditioEach user should determine film response and sensitivitythe specific conditions.

N. Dose calculation using a double-exposuretechnique

Klassen et al.50 used a double-exposure techniqueevaluate MD-55-2 as a high precision dosimeter using a C210 ~Varian! Spectrophotometer with 676 nm wavelengtUnknown doses, in the range 5–7 Gy, were given to a sefilms and the increase in OD was measured. Then a knodose of 6 Gy was given to each film and the increase inwas measured. In order to measure the change in sensitof the films between the first and second exposures, con

FIG. 10. Comparison of relative optical density for MD-55-2 film exposeduniform radiation fields with60Co gamma ray beam in~a! longitudinal and~b! transverse directions, respectively~Ref. 59!.

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films were given a known first dose of 6 Gy followed banother, known, dose of 6 Gy. The unknown dose to a fiwas calculated using its sensitivity to the second dosethe ratio of sensitivities derived from the control. Calculatin this fashion, the uncertainty in the unknown dose was lthan 1% between 5 and 7 Gy. The uncertainty is furtreduced when the unknown dose is close to the known di.e., when the ratio of the increase in OD for the first dosethe increase in OD for the second dose is the same as ththe control. Figure 13 is a representation of the increasOD with time of a first dose of 6 Gy followed by a secondose of 6 Gy. The dashed lines indicate the increase in Othe absence of exposure.50 The difference between the ne

FIG. 11. Responses of MD-55-2 film exposed to a uniform dose, 20 Gy,scanned with five different densitometers at Georgetown University~GU!,Henry Ford Hospital~HF!, National Institute of Standards and Technolo~NIST!, University of Kentucky~UK!, and Washington University~WU!~Ref. 69!.


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optical density 0.50 for the first dose of 6 Gy and the noptical density of 0.46 for the second dose of 6 Gy is cauby the slight decrease in sensitivity of the film as the toaccumulated dose increases, as well as the choice of wlength used for analysis.35

O. Shipping and handling

Any physical damage of the radiochromic films durinshipping or handling will introduce erroneous data in dosietric measurement. The color of the film will turn from cleto a milky white at the damaged location. Normally, thvendors provide the film between two layers of cardboasecurely placed in an additional box. However, occasionthe film may be damaged during the packing and shippand users should carefully examine the films when theyreceived and store and handle them very carefully. The fihave a slight tendency to pick up dust, probably due to stcharges on the outer layers, so before use the film shoulwiped clean with a lintless paper.50 The cut edges of the filmmay be stressed and should be avoided for dosimetry ansis. It is recommended to keep the light analyzing beabout 1.5 mm away from the cut edge.50

P. Summary characteristics of radiochromic films

Characteristics of the most commonly used radiochromfilms: HD-810 ~DM-1260!, MD-55-1, and MD-55-2 aresummarized in Table III.

Q. Summary procedures for radiochromic filmdosimetry

The following is a summary outline of considerations fradiochromic film dosimetry.

~1! Prior to use, films should be visually inspected ahandled with care.~See Sec. III O.!

~2! Films should always be kept in a dry and dark enronment at the temperature and humidity at which they wbe utilized for clinical purposes.~See Sec. III J.!

~3! Since the radiochromic films are sensitive to fluorecent light and to sunlight, they should be read and handlenormal incandescent light. If necessary, fluorescent ligand laboratory windows can be covered with commerciaavailable UV filters.57 ~See Sec. III J.!

~4! The film lot number and model number shouldnoted. This will allow the user to verify any variation in thmanufacturing of the film.~See Sec. III A.!

~5! The film orientation and alignment should be noteThis will allow the user to minimize the polarization effectnecessary.~See Sec. III F.!

~6! Since the film response changes with time, especiduring the first 24 h after irradiation, the exposure time areadout time for all the films should be documented andnecessary, appropriate correction factors for instabilitshould be applied. The recommendation is to read the fiat least 24 h28 ~preferably 48 h! after the exposure.~See Sec.III E.!

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~7! Film uniformity should be examined. If necessary tdouble-exposure technique should be considered to impfilm uniformity. ~See Sec. III L.!

~8! Radiochromic film should be calibrated using a larwell-characterized uniform radiation field.~See Sec. III M.!

~9! The dose response curve and film sensitivity shobe obtained in the dose range and conditions of interest.~SeeSec. III M.!

~10! The characteristics and/or limitations of your scaning densitometer should be considered. Several laser sning systems and CCD microdensitometer cameras are cmercially available for scanning radiochromic films.~SeeSec. IV!.

~11! The wavelength of the light in the densitometshould be nominally between 600 and 670 nm, which arewavelengths of the two main absorption peaks, thermaximizing the signal obtained from the system. Howeve

FIG. 12. Log plot of~A! net optical density and~B! net optical density perunit dose as a function of dose for MD-55-2 film.


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certain circumstances, in order to extend film range, lowwavelengths for readout~at the expense of contrast! are de-sirable.~See Sec. III K.!

IV. SCANNING DENSITOMETER SYSTEMS

Characteristics pertaining to various aspects of scanndensitometers are described in the following sections.

A. Techniques of two-dimensional data acquisition

There are two distinct approaches to the problem of hto perform two-dimensional densitometry. The more trational approach is to use a small light source and deteand then to translate the object being scanned. A slight vation to this approach is to translate the light source-deteinstead of the object being scanned. Common to both vations of this approach is that only a single point is measuat a time. As with manual, single-point densitometers, tsingle point consists of a light transmission measuremaveraged over the area of the defining aperture of the lsource, and also averaged over the absorbance spectruthe object being measured weighted by the wavelength strum of the light source and the efficiency of the light detetor. The resolution of such translational~moving! systems isthus governed by the size of the light source used, and bydistance between successive measurements.

A second approach to this measurement problem isuse of two-dimensional imaging systems. In this approacuniform light source illuminates the object being scannfrom the rear, and an imaging system~like a camera! is usedto measure light transmission from many points onsample simultaneously. The resolution of the scan is primrily governed by the pixel size of the imaging system onSuch systems have a speed of measurement advantagetraditional systems since data are acquired from all pointsthe sample simultaneously.

TABLE II. Film sensitivity calculation for MD-55-2 film exposed to Co-60

Dose~Gy! Optical density Net OD dose

0 0.312 ¯

1 0.334 0.02282 0.357 0.02295 0.421 0.02187 0.474 0.0232

10 0.522 0.021015 0.645 0.022220 0.752 0.022630 0.988 0.0225

50 1.303 0.019870 1.630 0.0188

100 2.233 0.0192150 2.910 0.0173200 3.759 0.0172300 4.012 0.0123500 3.998 0.0074700 3.993 0.0053

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B. Characteristics of light sources

Having introduced these two densitometry data acqution techniques, we now examine the common characterisof such systems. Of primary concern on all types of densmetry systems is the light source used for the absorbameasurements. The important characteristics for lisources are~1! emission spectrum;~2! size~for moving sys-tems!; ~3! uniformity ~for imaging systems!; ~4! outputstrength; and~5! polarization. For maximum sensitivity, thlight source spectrum should peak at the peak of the abbance spectrum of the sample being measured. Howeveminimum pixel size, laser sources are often used which hsharply defined wavelengths. Alternatives to lasers aretered white-light sources; fairly narrow~on the order of 10

FIG. 13. A schematic of how the OD of a dosimeter changes as the resua first dose of 6 Gy, given at 0 days, and a second dose of 6 Gy, givendays. The sensitivity drops 8% at 7 days. In each case, the OD is read 2after irradiation. The dashed lines indicate the change in OD which wohave taken place in the absence of the irradiation~Ref. 50!.


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nm full width at half-maximum! emission spectra are possible using interference filters. The disadvantage of usfiltered sources is the loss of light source strength whlimits the ability to make measurements at higher optidensities. For imaging systems, the uniformity of the ligsource is also a very important parameter. In principle, nuniformity of the light source in such systems can becounted for by making images of the bare light source adigitally correcting sample images for observed light sounonuniformities. A typical approach to making large-aruniform light sources is to use a bank of light-emitting dodes~LEDs! behind a light-diffusing surface. Use of LEDhas the advantage that a number of narrow emission specentered at different wavelengths are available. When lasources are used, it is necessary to have the sample mouon a light-diffusing surface so as to avoid interference frinartifacts caused by reflections on plate and sample surfac70

C. Characteristics of light detectors

Important characteristics for light detectors are~1! sensi-tivity; ~2! spectral efficiency;~3! linearity; and ~4! signalresolution. The most sensitive light detectors for absorbameasurements usually employ some sort of transmitted pton counting. For single-point~and moving! systems the tra-ditional detector is the photomultiplier tube~PMT! operatedin the current mode for low absorbance/high signal measments or in the pulse counting mode for high absorbance/signal measurements. Spectral efficiencies for most commPMTs are well known and easily obtainable from produliterature. Of greater concern is the linearity of these stems. Factors which affect PMT detector linearity are couing losses at high pulse rates~low absorbance levels!, andpossible nonlinearities at changeover points from pucounting to current modes.

Other, though generally less sensitive detection systeemploy solid state detectors. The most sensitive imaging

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TABLE III. Characteristics of radiochromic films.

Characteristic

Radiochromic film

HL-810~DM-1260! MD-55-1 MD-55-2

Nuclear Assoc. No. — 37-041 37-041Nominal dose range~Gy! 50–2500 10–100 3–100Effective Z 6.0–6.5 6.0–6.5 6.0–6.5Postirrad. color stability with time 24 h~Sec. III E! 24 h ~Sec. III E! 24 h ~Sec. III E!40 keV response relative to60Co 0.7~Sec. III G! 0.6 ~Sec. III G! 0.6 ~Sec. III G!Dose fraction effect ,1% ,1% ,1%Dose rate effect ,5% ~Sec. III I! ,5% ~Sec. III I! .60 Gy 10%

,60 Gy Nonea

Humidity effect ,2%~Sec. III J 1!

,2%~Sec. III J 1!

,2%~Sec. III J 1!

Temperature effect Yes~Sec. III J 2! Yes ~Sec. III J 2! Yes ~Sec. III J 2!Ultraviolet sensitivity Yes~Sec. III J 3! Yes ~Sec. III J 3! Yes ~Sec. III J 3!Image resolution .600 cycles/mm

~1200 lines/mm!.600 cycles/mm~1200 lines/mm!

.600 cycles/mm~1200 lines/mm!

Uniformity ~RSD! 7% ~Ref. 39! 3%–5% 3%–5%

aReference 35.

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tems utilize banks of charge-coupled device~CCD! detec-tors. Quite high densities of such devices are obtainable,sensitivity is comparable to PMTs. In considering suchvices for densitometry, one needs to be aware of the speefficiency relative to the light source used.

Finally, an important consideration for all types of detetor systems is the signal resolution. It is generally specifiin terms of the number of discrete density steps~shades ofgrey! that the detector is capable of. Signal resolution is aoften specified in terms of the number of bits of informatiper pixel. Thus, for example, an 8 bit device is capableresolving only 256 shades of grey.

D. System response spatial resolution linearity

The overall light source/detector linearity is generallyvestigated in the course of preparing a calibration curvethe system. This process involves applying known doseradiation to individual samples, and looking at the functiof measured optical density versus delivered absorbed dSince the properties of the dosimetry medium may influethe shape of the calibration curve, a better way to investigdetector system linearity is through the use of calibrated ntral density filters. Such filters have a relatively flat absbance spectrum and are uniform in density over fairly laareas. They can be calibrated using high-quality spectroptometers, and generally consist of a stable metal evaporonto quartz or glass.71 By comparing the density read witthe system under test with the density as indicated by a strophotometer, one can have a reliable method of determing system linearity independent of the imaging mediuThis is useful since it may indicate that it is the reader stem rather that the imaging medium that causes a calibracurve to flatten at higher dose levels. Also one may find tthere is an optimal density region in terms of relative stdard deviation of measured densities. Generally this willbe at a low density because of ‘‘background’’ density of tnonirradiated medium, or at high densities because of lactransmitted light causing poor signal-to-noise ratios.

E. Spatial resolution

The spatial resolution of any imaging system is generaquantified by the number of resolvable line pairs per mimeter. Factors which govern resolution for moving systeare ~1! light source size and~2! minimum space betweesuccessive readings. For imaging systems, resolution iserned by~1! pixel size and~2! amount of ‘‘dead’’ area be-tween sensitive elements of the imaging array. Resolutioboth types of systems is also limited by~1! light diffusion inthe sample and~2! stray light in the reader. Spatial resolutiofor any system is best evaluated by reading a standardpair pattern and determining the maximum number of resoable line pairs/mm. An interesting feature of imaging dentometers is the possibility to vary the pixel size by changthe position of the imaging detector relative to the ligsource/sample plane. Thus, while the moving systems msingle measurements which are basically only samplesthe light source size, the imaging systems provide sam


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averaged over the pixel size, with the only information thalost being that in the ‘‘dead’’ area between pixels. Anothimportant consideration for moving systems is the rangeposition steps available. Obviously, step increments msmaller than the size of the light source are not of much uOn the other hand, one does not want to be unduly limitedthe largest stepping increment made available, sincewould produce prohibitively large data files for modest sizsamples.

F. Positional accuracy

An important parameter in any two-dimensional densimeter is the positional accuracy of the resulting image.moving systems, this is effected by the accuracy of the sping increment between measurement points. For imagsystems, the regularity of the imaging grid affects the resing accuracy of the image. For both types of systems, ptional accuracy may be determined by scanning regularpatterns and comparing the resulting images to the knogrid dimensions.31,72 A significant caveat for systems whictranslate the sample and/or the light source/detector sysis whether the motion is bidirectional or not. While bidiretional motion increases readout speed, it may introducesitioning errors in alternate scanning rows due to effects sas gear backlash when the direction is reversed. Examplethis effect are shown~unintentionally! in the jagged isodosecontours of Soares,30 which could subsequently be correcteto make smooth isodose contours viewed both topogracally and orthographically.38

An unavailable feature in many scanning systems isability to position samples in a reproducible manner onscanning bed. This is an important consideration when aries of films that have been irradiated simultaneously instack are to be read. Since the scanning system returns cdinates based on the scanning bed and not on the film itthe user is left with the problem of registering the varioimages ~coordinate systems! of the stack of films. In theworst case this involves both translational and rotationalordinate transformations. Similar problems arise when mtiple readings of the same sample are desired, such asby pixel sensitivity corrections based on readouts beforeafter irradiation.36 Either fiducial marks on the film or imagewhich include the edges of the film are necessary to msuch registration corrections.38 On the other hand, if thescanning bed has provisions for positioning samples whigh reproducibility, these difficulties can be largely avoideOne suggestion has been to include small pegs on the sabed that fit into prepared holes in each sample.72 Since inmedical dosimetry one is very often interested in thredimensional dose distributions, such a consideration forassembling a stack of two-dimensional images is an imptant one. Another important parameter associated withscanning bed is the size of the sample that can be read.imaging systems this is limited by the size of the uniforbacklighting surface. Most moving systems are designedaccept at least a 20 cm325 cm ~8 in.310 in.! sample, withconventional x-ray film in mind.

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G. Acquisition time

A very practical consideration in sample reading is ttime necessary to acquire the scan data. Obviously therespeed advantage when an imaging system is used sincthe data are acquired simultaneously. Other factors whaffect data acquisition time for moving systems are~1! thetime necessary to make an individual measurement,~2! thetime necessary to step to the next position, and for systwhich transfer data to a host computer,~3! the time neces-sary to transfer the data.

H. Control software

It is often the case that the software supplied withscanning system for manipulating the image data limitsuser to only those operations anticipated by the softwaresigner. In practice, users may need operations that aresupported by the software supplied. For this reason, softwshould be as flexible as possible, but even more importanit is essential that the user be able to access the opticalsity data in a format that can be transferred to other softwpackages. Documentation supplied with the scanning sysshould clearly indicate how to do this operation. The muniversally acceptable form~although probably the bulkiesas well! is an ASCII format of thex and y coordinates fol-lowed by a quantity proportional to the measured optidensity. In any event, supplied software should be capableast of displaying the scanned image, preferably in coThe ability to produce isodensity contours is also desiraIt is also important to be able to convert the density dataabsorbed dose using a user-generated calibration curve.feature is essential in nonlinear systems to avoid confusbetween isodensity plots and isodose plots.

I. Environmental factors

Finally, it is important to consider several characteristwhich may best be described as ‘‘environmental’’ factoChief among these is the temperature that the samplereach in the course of readout28 as well as postirradiation.65

If the temperature of the sample becomes significantly abroom temperature, the user should make a note of the amof time taken for this to occur as well as the time that helapsed since the beginning of the scan. This is a veryportant parameter for some dosimetry media such as poacetylene thin-coated film, which exhibits a temperaturependence in its absorbance spectrum.28 For certainwavelengths, a modest change in temperature can be mfied into a significant change in optical density becausewavelengths lie on a steep portion of the absorption sptrum. Another important factor is the type of interior lightinemployed during sample loading and positioning. Some stems use fluorescent lights that contain a significant ultralet component; some dosimetry media are sensitive tocomponent and spurious optical density changes can oduring sample setup.


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J. Specifications of some scanning densitometersystems

Specifications of some scanning densitometers are smarized in Table IV.

V. MEDICAL APPLICATIONS OF RADIOCHROMICFILMS

The radiochromic films are relatively insensitive to radtion compared to commonly available detectors usedmedical applications. This lack of sensitivity makes theideal for dosimetry where high doses are utilized. An eample of such a situation is the dosimetry in the immedivicinity of brachytherapy sources. Because of the invesquare law, radiation doses at points close to the sourcebe very high, which becomes a problem with conventiodetectors. Another important characteristic of radiochromfilms is that they have an elemental composition close toof water, which reduces their sensitivity to photon energyapplications dealing with determination of dose deliveredwater. Finally, the radiochromic films are available in tform of a two-dimensional dosimeter. These dosimeters nto be calibrated prior to use~see Sec. III!. Some of the ap-plications in medicine which are based on the abomentioned features of radiochromic films are describedthis section.

A. Ophthalmic applicator dosimetry

Although 90Sr ophthalmic applicators have been useddecades, problems with their dosimetry have been resoonly recently. Until recently, there was no standardizmethod for calibration of the dose rate at a reference distain a medium; discrepancies of up to 50% were reportedGoetsch73 in 1989. Subsequently, this discrepancy wassolved and a standardized method for the calibration of thapplicators was reported by Soares.30,74During this develop-ment, it became clear that the calibration of ophthalmicplicators should be based on the determination of surfabsorbed dose rate to water averaged over an approparea, and that relative dose profiles should also be demined to completely specify the two-dimensional dose dtributions produced by these applicators. Because of thetremely high dose rates produced by these applicators,radiochromic film proved to be an ideal detector for the dtermination of dose profiles, as demonstrated in a seriepapers from NIST by Soares.30,75

In 1991, Sayeg and Gregory61 described a techniquewhich enables them to obtain detailed dose characteristic90Sr beta-ray ophthalmic applicators. A radiochromic radtion detector was used to determine the surface dose ratedose distribution of these sources. The detectors were fouseful for this application due to the high surface dose [email protected]–1.0 Gy/s# and their low sensitivity~approximately104 Gy for an optical density of 1.0!. The films were evalu-ated on a He–Ne scanning laser densitometer with a restion of 0.3mm. Comparison with NIST extrapolation ionization chamber measurements indicated surface doseagreement within 6%.

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Also in 1991, Soares30 described the use of radiochromfilm for source profiling. The films were used to map dosrate variations at applicator surfaces. The films were rusing a scanning laser densitometer~LKB Pharmacia model2222-020! at 633 nm, which is near one of the peaks in tfilm absorbance spectrum. The spot size of the laser wasmm in diameter, and the step size for scanning was adjable in 40mm increments in both dimensions. The accuraof the stepping increment was checked by scanning a miscope stage micrometer and a NIST glass scale. The abslinear accuracy of the system was found to be accuratless than 1mm. Soares30 calibrated these radiochromic filmusing well-characterized60Co gamma-ray beams. To checthis, calibrations were performed using both60Co gammarays and90Y beta particles. The latter was done using tprotection-level sources used at NIST for instrument asource calibrations. There is agreement between NISTthe National Standard Laboratory of Germany, PhysikalisTechnische Bundesanstalt~PTB! on the dose rate from thessources at the prescribed distances. Furthermore, it hasshown that radiochromic film response to electron beamradiation is the same as the response to Co-60 gammawithin the estimated uncertainty of measurement~65% at95% confidence level!.28,76

B. Brachytherapy dosimetry

Because the dose gradients around brachytherapy soare steep, the high spatial resolution offered by film dosetry is an advantage over other detectors such as thermminescent dosimeters~TLDs!. In 1991, Muenchet al.39 ex-plored applications of radiochromic film for dosimetry nebrachytherapy sources. Dose distribution in the immedvicinity of a high activity ~370 GBq! brachytherapy192Irsource was mapped using radiochromic film. They compathe photon energy dependence of the sensitivitiesGafChromic film, silver halide verification film~Kodak X-Omat V Film!, and lithium fluoride TLDs~Harshaw! overthe photon energy range 28 keV–1.7 MeV, which is ofterest in brachytherapy. For more discussion on the enedependence, see Sec. III.

C. Interface dosimetry

Dose perturbation at tissue-metal dental interfacesbeen studied by several investigators.77–79 In 1991 Farahaniet al.77 used radiochromic films to investigate the enhanment of dose to soft tissue~or water! close to high electron-density materials and to measure the detailed lateraldepth-dose profiles in soft-tissue-simulating polymer adcent to planar interfaces of several higher atomic-nummaterials of interest in dental restoration: 18 carat gold dtal casting alloy; Ag–Hg dental amalgam alloy; Ni–Cr detal casting alloy: and natural human tooth structure. Intleaved stacks of calibrated thin radiochromic dosimeter fiand tissue-simulation polymer were used for these measments. Assemblies of these polymer–dosimeter stacksboth sides of the dental materials were irradiated in one fidirection by collimated60Co gamma-ray or 10 MV x-ray


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beams directed perpendicularly to the material interfacesanother test, designed to simulate more closely therapetreatment conditions, a phantom constructed on both sidea row of restored and unrestored whole teeth~restorationmaterials; gold alloy crown; Ni–Cr alloy crown; Ag–Hmesial-occlusal-distal~MOD! amalgam filling; unrestoredtooth! was irradiated in one fixed direction by the collimatephoton beams. Their results indicated that the doenhancement in ‘‘tissue’’ is as great as a factor of 2 onbackscatter side adjacent to gold and a factor of 1.2 adjato tooth tissue, but is insignificant on the forward-scatter sbecause of the predominant effect of attenuation by the hdensity, high atomic-number absorbing material.

D. Stereotactic radiosurgery dosimetry

In 1990, Bjarngardet al.80 used radiochromic film to in-vestigate the effects of electron disequilibrium for smfields used for irradiation of intracranial lesions. For ra,1.0 cm the dose on the central axis was shown to progsively diminish due to electron disequilibrium. This leadsmeasurement artifacts when the detector is too large, asreadily observed with ionization chambers. Radiographic aradiochromic films were used with densitometric evaluatto provide the resolution necessary to measure absodoses for the narrowest beams. The contributionphantom-scattered photons was significant even at smallsizes, and scatter factors were determined from the expmental results. Photons scattered by the auxiliary collimadid not add appreciably to the dose on the central axis.data were used to characterize the dose-to-kerma ratiofunction of beam radius.

In 1994, McLaughlinet al.38 addressed similar problemrelated to the dosimetry of small fields. As a demonstratof suitability, the calibrated radiochromic film was usedmeasure the dose characteristics for the 18, 14, 8, and 4fields from the gamma-ray stereotactic surgery units at MClinic and the University of Pittsburgh. Intercomparisonsradiochromic film with conventional methods of dosimetand vendor-supplied computational dose planning sysvalues indicated agreement to within62%. McLaughlinet al.38 concluded that the dose, dose profiles, and isodcurves obtained with radiochromic film can provide higspatial-resolution information of value for acceptance testand quality control of dose measurement and/or calculat

E. Dosimetry in the penumbra region of radiotherapybeams

During the commissioning of a multileaf collimator sytem, Galvinet al.81 used radiochromic film to investigate anpotential distortions of the dose distribution at an edge duchanging energy sensitivity of silver bromide film. Standaradiographic film was used for the penumbra measuremand separate experiments using radiochromic film and tmoluminescent dosimeters were performed to verify that dtortions of the dose distribution at an edge due to chang


TABLE IV. Specifications of some scanning densitometer systems.

Maker Model Scan mode

Light source

Type Wavelengths Size

LKB Pharmacia UltroScan XL Translational HeNe laser 633 nm 100mm spotor 503800

mm rectangleMolecular Dynamics Personal densitometer Translational 1 mW HeNe laser 633 nm 50mm

~FW2s!Gaussian spot

Zeineh Soft laser scanningdensitometer

HeNe Laser 635 nm 50mm

Vision Ten V SCAN Imaging Filtered white light 670 nm ¯

Bio-Rad GS-670 Translational/imaging Filtered fluorescentlight bed

400–750 nm ¯

Photoelectron Corporation CMR-604 CMR-608 Imaging LED light bed 665 nm~20 nm FWHM!470–940 nm

available

¯

Vidar Systems Corporation VXR-12 Translational/imaging Standard fluorescent light Broadband 168mmAGFA Arcus II Translational/imaging Standard fluorescent light Broadband 168mm

Lumisys Lumiscan 75/Lumiscan 150

Translational/imaging Laser 633 nm 100mm spot/2 K5100mm/1 K5175mm/

variable100–420mm/high resolut.50–420mm

Maker Detector type

Resolution

Pixels Density rangeSpatial Signal

LKB Pharmacia 20mm and 40–600mmin 40mm steps

12 bit ~4096 shades of grey!over 0–10 OD

Variable 0–4 OD

Molecular Dynamics PMT 50 or 100mm 8 or 12 bit selectable Variable 0–4 ODZeineh 100mm 8 bit

Vision Ten CCD 50, 87 or 105mm 12 bit 84331280 to409635000

0–3.5 OD

Bio-Rad Linear CCD 58mm ~variable! 40003variable 0–2.5 ODPhotoelectron Corporation Cooled CCD minimum 273 23 mm

~variable!16 bit 2423375 0–2.4 OD

Vidar Systems Corporation Linear CCD 85, 168, 339, or 423mm 12 bit Variable 0–2.6 ODAGFA Linear CCD 21, 28, 42, 85, 168, 353mm 12 bit Variable 0–2.5 OD

Lumisys Linear CCD 100–175mm/variable 12 bit 204832500/variable 0–3.5 OD

Maker Bed type Bed size Scan speed Acquisition time

LKB Pharmacia White diffusedfluorescent during setup

22325 cm 42 mm/s 1003100 pixels in 40 m~ASCII! 2003200 pixels

in 40 min ~binary!Molecular Dynamics Low

fluorescent clear glass20325 cm 7 lines/s 20325 cm

sample in 6–12 minZeineh Line scanner

15 cm35 mm10 s per scan line

Vision Ten 35 cm width, anylength.7.5 cm

100 lines/s

Bio-Rad 30343 cm 1–15 minPhotoelectron Corporation White diffused 9.6312.2 cm or

19.6324.6 cm0.5 min

Vidar SystemsCorporation

Vertical feed 35343 cm 51 s for 36 cm343 cm film atmax resolution

AGFA 21335 cm 250 lines/s 25320 cm filmat 352mm

digital resolution;50 sLumisys Vertical feed 17335 cm 115 lines/s 21.5327.8 cm

film at 200mmpixel size;15 s



TABLE IV. ~Continued.!

Maker Interfaces File formats Price Users

LKB Pharmacia Serial RS232~9600 bODd!, parallel~Centronics!

Coded Binary, ASCII $15 K NISTVanderbilt

Henry Ford HospitalMolecular Dynamics Serial, parallel, thin wire ethernet 8 and 16 bit TIFF $20 K Washington Univ. Univ. of TX

MD AndersonUniv. of WICalib. Lab.

Zeineh IBM Univ. of KYVision Ten IBM AT Bus, SCSI $12K Henry Ford Hospital

Bio-Rad PC, GPIBPhotoelectron Corporation Serial RS232~115.2 kbODd maximum! TIFF, FITS NISTVidar Systems Corporation SCSI TIFF, BMP $16 K Pennsylvania Hospital

York Cancer CenterRIT 113

AGFA SCSI TIFF, BMP $22 K Loma Linda Univ. RIT 113Lumisys PC, SCSI TIFF-Binary $30 K Georgetown Univ.

NIHRIT 113

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energy sensitivity of silver bromide film are negligible. Filmwere analyzed with a scanning laser densitometer with amm spot size.

F. Hot particle dosimetry

In 1990, Soareset al.82 presented preliminary results othe measurement of the distribution of skin doses fromparticles which are micron size particles containing radiotive materials, in this study of60Co. Hot particles are a concern in the environment of a nuclear reactor becauserepresent a potential source of harmful radiation exposurnuclear workers. This work was also a first demonstrationthe high resolution dosimetry that is possible with radiochmic film.

The two-dimensional dose profile was obtained in the flowing manner. A particle of suitable nominal size and ativity was selected. The60Co activity was measured at NISusing Ge~Li ! spectrometry as 62mCi. The diameter wasmeasured with a traveling stage microscope as 277mm. Theradiochromic film was then taped to a polystyrene block aa tape strip containing the particle was stretched overfilm, and the edges were taped down to keep the particlcontact with the sensor film. For measurements at 7 mg/2

~the tissue depth of interest in nonpenetrating radiation ptection!, additional layers of Mylar™ were inserted betwethe hot particle and the sensor film. For these measuremexposures were made for various times between 1 and 16For depth dose profiling, a stack of 12 films was exposed120 h. The film was then read out with a 40mm step size.The optical absorbance for the scan file was then conveto absorbed dose rate using the exposure time and thedose-calibration curve based on the NIST60Co standard poosource. The data files, typically 2500x–y points, were trans-ferred to a PC for plotting using a three-dimensional graphroutine.

In a subsequent study reported in 1991 at the same itution by a team led by McWilliams,83 an attempt to standardize hot particle dosimetry was made through the gention and characterization of60Co spheres. An electron arcrapid solidification process was used to produce uniform


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balt alloy spherical particles of various diameters rangfrom 50 to 300mm. Neutron activation of selected particleyielded essentially pure60Co in the MBq range. The particlewere characterized by physical size and activity. Dose rawere determined using extrapolation chamber and radiocmic dye film measurements. Having simple geometries, thparticles were found to be ideal for the development atesting of calculational methods and benchmarking of coputer codes designed to assess shallow dose. Some oexperiments performed at NIST dealing with precisisource profiling using radiochromic film were also presenin a 1993 review by Walkeret al.84 and another by Soareand McLaughlin.31 A dosimetry intercomparison of hotparticle dosimetry has recently been reported on whichvolved two groups using radiochromic film.85

G. Dosimetry for radiation inactivation and target sizeanalysis

Large doses in the range of hundreds of kGy are necsary for the inactivation of some proteins active in cellumetabolism. From a knowledge of accurate dosimetry in thigh dose range and the shape of the inactivation dosesponse curve, it is possible to ascertain the molecular sizputative proteins~or other targets!. One such application using radiochromic detectors was reported by Van Hoet al.86 in 1992. Dosimetry was performed using 131 cmpieces of ‘‘radiochromic nylon,’’ 50mm thickness film do-simeters, of which the optical density change at 510 nafter irradiation, was measured using a Far West TechnolFWT-92 radiochromic reader.86 The dose received was determined from the difference in optical density. The calibrtion was checked against irradiation in a60Co gamma-raybeam and found to agree within 1% with the source calibtion using Fricke ferrous sulphate dosimetry. The functiounit size of the water channel in rabbit erythrocytes wassessed using target size analysis following radiation inacttion. Using radiochromic nylon dosimetry, accurate valuesaccumulated dose yielded an absolute target analysis, leato direct determination of molecular size.

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H. Intravascular brachytherapy dosimetry

A special application which is ideally suited for radiochromic film dosimetry is the characterization of the dodistributions around intravascular brachytherapy sourcThe dimensions of these sources are comparable to ‘‘hotticles’’ ~see Sec. II F! and dosimetry information is neededdistances of 2–5 mm from the source axis, which are smathan those encountered in conventional brachytheraSoareset al.87 have reported on the use of radiochromic fidosimetry in conjunction with extrapolation chamber mesurements for the calibration and characterization90Sr190Y catheter-based intravascular brachytherasources. Dugganet al.88 are using films to perform dosimetrmeasurements on32P coated stents for permanent implaOther groups are in the process of similar studies on cathebased32P sources89 and activated Ni–Ti stents.90

I. Proton dosimetry

The radiochromic films have been found to be a usedetector for dosimetry measurements in clinical probeams.76,91,92The DM-1260 has been used by the NationInstitute of Standards and Technology, NIST, in the US athe Institute for Theoretical and Experimental Physics, ITEin Moscow, to investigate the dosimetric characteristics opulsed proton beam~0.1 ms pulse, 2.5 s interval, 73106 Gy/s peak intensity, 10 Gy/min average dose rate! forclinical applications.91 The results of this investigation indicate that the response of DM-1260 film to a proton beamscanned with the NIST LKB HeNe laser scanner, was lin~;4.4% for one standard deviation! within the dose region50–170 Gy.91

More recently, the more sensitive MD-55-2 film has beused for clinical proton dosimetry.76,92 The studies of theMD-55-2 film in different beams have shown a similar lineresponse within the dose region 10–100 Gy for high enephoton, electron, and proton beams, except when theyirradiated in a proton beam at the Bragg peak location.76 TheMD-55-2 film exhibits an apparent suppression of the d~5%–10%! in the Bragg peak region, however, the differenin penetration of the beam at the depth of 80%–50% didose fall-off measured with the MD-55 film and the ioniztion chamber is within 0.1–0.2 mm.

The MD-55-2 film was also used to measure compdose distributions in an irradiated phantom, thus enabverification of dose delivery of proton Bragg peak stereottic radiosurgery with multiple noncoplanar beams.92 The ra-diochromic film dosimetry validated the prescribed doselivery to within 65% ~one standard deviation!. The spatialresolution of the phantom verification technique was suthat possible misalignments greater than 2 mm, could betected. The radiochromic films were evaluated with the R113 film dosimetry scanner system~RIT, Denver, CO!. In-cluded in this system was an AGFA Model Argus II scannwith daylight fluorescent lamp, and a CCD array and soware for film analysis. To eliminate noise in the film andimprove film uniformity to62%, films were scanned withdigitized resolution of 85mm and larger.


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VI. PROCEDURE SUMMARY FOR RADIOCHROMICFILM DOSIMETRY

The following summarizes the recommended procedfor radiochromic film dosimetry

~1! When selecting a scanning densitometer, the signanoise ratio of the scanning equipment should be keptmind. An 8 bit densitometer only provides 256 shadesgrey, which may not be enough to give good images at ldose levels.~See Sec. IV.!

~2! The characteristics and/or limitations of your scaning densitometer should be considered. Several laser sning systems and CCD microdensitometer cameras are cmercially available for scanning radiochromic films.~SeeSec. IV.!

~3! The maximum optical density for which the densitmetry system will provide a reading should be known. Thshould be verified and acceptable for intended use.

~4! The sensitive emulsion layer~s! of radiochromic filmsabsorbs most strongly in the red wavelength~about 660 nm!region. Thus the densitometer response is optimized at thwavelengths.~See Secs. II and IV.!

It is desirable to have the wavelength of the light souin the densitometer between 600 and 670 nm, which arewavelengths of the two main absorption peaks, theremaximizing the signal obtained from the system. Howevershould be kept in mind that in certain circumstances, in orto extend film range, lower wavelengths for readout~at theexpense of contrast! are desirable.~See Sec. III K.!

~5! It must be kept in mind that the measured opticdensity is determined by the absorption spectrum of the ssitive emulsion layer~s! of the film as well as the spectrum othe readout~scanner! light source. Thus the use of a broaband light source, such as white light, may not yield tdesired contrast levels, especially when used with an 8pixel depth.

~6! Prior to use, films should be visually inspected ahandled with care.~See Sec. III O.!

~7! Films should always be kept in a dry and dark enronment at the temperature and humidity at which they wbe utilized for clinical purposes.~See Sec. III J.!

~8! Since the radiochromic films are sensitive to fluorecent light and to sunlight, they should be read and handlenormal incandescent light. If necessary, fluorescent ligand laboratory windows can be covered with commerciaavailable UV filters.57 ~See Sec. III J.!

~9! The lot number and model number of the film shoube noted. This will allow the user to verify any variationthe manufacturing of the film.~See Sec. III A.!

~10! The film orientation and alignment should be noteThis would allow us to minimize the polarization effectneeded.~See Sec. III F.!

~11! Since the film response changes with time, escially during the first 24 h after irradiation, the exposure timand readout time for all the films should be documented aif necessary, appropriate correction factors for instabilitshould be applied. The recommendation is to read the fi

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at least 24 h28 ~preferably 48 h! after the exposure.~See Sec.III E.!

~12! Film uniformity should be examined. If necessarthe double-exposure technique should be considered toprove film uniformity.~See Sec. III L.!

~13! Radiochromic film should be calibrated using a larwell-characterized uniform radiation field.~See Sec. III M.!

~14! The dose response curve and film sensitivity shobe obtained in the dose range and conditions of interest.~SeeSec. III M.!

VII. FUTURE DIRECTIONS

This report documents the considerable effort thatgone into the development of radiochromic film as a valuadosimeter for both medicine and industry. It is clear that twork is not finished, and further improvements in the chacteristics of the films presently available can be expecFor example, producing radiochromic films with greater ssitivity could open the possibility for using these materiafor diagnostic imaging and personnel dosimetry. It wpointed out in Secs. II and III that the manufacture of radchromic film with an increased thickness of the sensor layand hence an increased sensitivity to radiation, has beencomplished in the past few years. This change in sensitiis about a factor of 4 for an optical density of 2.0. This sleaves more than a tenfold difference compared to evenleast sensitive radiographic films. Standard radiotherverification ~Kodak XV! film is some 30 times more senstive than the most sensitive radiochromic film. However, iproved sensitivity for radiochromic film may be possiblethe future.

Additional effort must be focused on improving the hmogeneity of the distribution of the dye layer for the radchromic films. The double-exposure technique describedSec. III is a clever way of compensating for any irregularin the sensor layer, but it lacks both the efficiency and prticality needed for routine utilization of this dosimeter. Hmogeneous distribution of the dye layer is a technical prlem that should be solvable by the manufacturer,increased use of radiochromic film may be needed to serva stimulus for pursuing an acceptable solution.

Two improvements in the software and hardware desof scanning densitometer systems were suggested in SecThe first was a recommendation that scanner manufactuprovide easy file transfer to an alternative software packcapable of analyzing raw scan data. Ideally, a selectiontransfer file formats should be provided so that the user dnot have to rewrite the information. As mentioned in Sec.the preferred format is a string of ASCII data consisting oxandy coordinates coupled with an optical density value. Tsecond suggestion was improvement in the spatial indeof films in scanning densitometer system. A few flatbscanners have a raised border along the top and one sithe sensitive scanning area. This feature can be used fodexing by pushing film against the two edges before scning. Hopefully, more manufacturers will adopt this simpinnovation in the future. For scanners where the film


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dropped in a bin, the use of fiducial markers of some smay be necessary.

Section V discussed a number of applications where ctain features of radiochromic film have been used to anvantage. These features can be listed as follows. First,reduced sensitivity of radiochromic film can be helpful whmeasurements are made in regions with an extremely hdose rate. Second, the importance of being able to haradiochromic film in normal room light should not be undeestimated. This feature overcomes a major disadvantagradiographic film. Handling the film in room light alloweasy cutting of the material to conform to irregular shapand the film can be neatly wrapped around curved surfaThird, compared to radiographic film, radiochromic film ha relatively small change in response as photon or elecenergy changes. Utilizing this feature it is possible to obthigh-resolution measurements in regions where the enespectrum of a radiation beam is changing. Fourth, the vsmall volume of this dosimeter~dye thickness multiplied bythe area of the spot size of the densitometer used for ansis! makes it valuable for measurements where other devare not suitable. Given these unique features and the pobility of combining them in various ways, it is anticipatethat there will be an explosion of new and interesting usesradiochromic film.

Instead of two-dimensional imaging on thin films, italso possible to produce high-resolution three-dimensioradiographic registration on clear gels or block polymecontaining leuco dyes,11 acid-forming halogenated hydrocabons containing indicator dye,12 or a gel solution of ferroussulfate in the presence of benzoic acid and an indicatorthat upon irradiation forms a highly colored ferric-ion complex with the dye.93 Although a detailed description of thinew technology is not included as part of the current repit is creating considerable excitement in the medical commnity and is mentioned in this section on future developmeto provide the reader with a few key references. Enthusiaabout the use of gels seems to center on the possibilitmeasuring three-dimensional~3D! dose distributions withoutthe problem of having to accurately register a series of filin 3D space. Instead, a solid gel can be irradiated and cutthin sections for analysis, or analyzed in 3D with a MRsystem. There is also an effort underway to develop an ocal CT-type system for 3D readout.94,95

In summary, medical physicists have already developenumber of important applications for radiochromic filmHowever, since this dosimeter possesses a number of unfeatures, it is anticipated that with use of this dosimeterwater, we will see an explosion of new and interesting uof radiochromic films.

1W. L. McLaughlin, J. C. Humphreys, D. Hocken, and W. J. Chapp‘‘Radiochromic dosimetry for validation and commissioning of industrradiation processes,’’ inProgress in Radiation Processing, Proceedingsof the Sixth International Meeting, Ottawa, 1987, edited by F. M. Fra@Radiat. Phys. Chem.31, 505–514~1988!#.

2W. L. McLaughlin, ‘‘Novel radiation dosimetry systems,’’ invited papein High Dose Dosimetry for Radiation Processing, Proceedings of Inter-

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national Symposium, Vienna, 1990, STI/PUB/846~International AtomicEnergy Agency, Vienna, 1991!, pp. 3–27.

3L. Chalkley, ‘‘Photometric papers sensitive only to short wave ultravlet,’’ J. Opt. Soc. Am.42, 387–392~1952!.

4W. L. McLaughlin, A. Miller, R. M. Uribe, S. Kronenberg, and C. RSiebentritt, ‘‘Energy dependence of radiochromic dosimeter responsx- and rays,’’ inHigh Dose Dosimetry, Proceedings of the InternationaSymposium, Vienna, 1984, STI/PUB/671~International Atomic EnergyAgency, Vienna, 1985!, pp. 397–424.

5C. D. Hillyer, J. M. Hall, D. A. Lackey, and D. E. Wazer, ‘‘Developmenof a colorimetric dosimeter for quality control of blood unit and irraditors,’’ Transfusion33 ~1993!.

6W. L. McLaughlin, in Ref. 2, pp. 1–27.7W. L. McLaughlin and K. P. J. O’Hara,The importance of referenceStandard and Routine Absorbed dose measurement in Blood Irradia,Proceedings of the American Association of Blood Banks Annual Meing, Orlando, FL, 1990~American Association of Blood Banks, BethesdMD, 1996!, pp. 237–245.

8J. Kosar,Light-Sensitive Systems~Wiley, New York, 1965!.9G. H. Dorion and A. F. Wiebe,Photochromism~The Focal Press, Lon-don, 1970!.

10Photochromism, edited by G. H. Brown~Wiley-Interscience, New York1971!.

11W. L. McLaughlin, ‘‘Film, Dyes, and Photographic Systems,’’ inManualon Radiation Dosimetry, edited by N. W. Holm and R. J. Berry~Dekker,New York, 1970!, Chap. 6, pp. 129–177.

12W. L. McLaughlin, ‘‘Radiochromic dye-cyanide dosimeters,’’ in Ref. 1pp. 377–385.

13W. L. McLaughlin, ‘‘Dosimetry: New approaches,’’ invited paper inPro-ceedings of the International Conference on Radiation-Tolerant PlaScintillators and Detectors, Tallahassee, 1992, edited by K. J. Johnsand R. L. Clough@ Radiat. Phys. Chem.41, 45–56~1993!#.

14J. B. Rust, J. D. Margerum, and L. J. Miller, ‘‘Light-Scattering Imaginby Photopolymerization,’’ inNovel Imaging Systems, Proceedings ofSeminar, Washington, DC, edited by R. D. Murray~Society for ImagingScience and Technology, Boston, 1969!, Chap. 14, pp. 173–186.

15W. R. Lawton, ‘‘Recent Advances in Organic-based Imaging Systemin Ref. 14, Chap. 6, pp. 63–77.

16J. S. Arney, ‘‘Kinetic and mechanical descriptions of the microencaplated acrylate imaging process,’’ J. Imaging Sci.33, 1–6 ~1989!.

17J. D. Margerum and L. J. Miller, ‘‘Photochromic Processes by Todtoerism,’’ in Photochromism, Techniques of Chemistry, edited by G. H.Brown ~Wiley, New York, 1971!, Vol. III, Chap. 6, pp. 557–632.

18W. L. McLaughlin and L. Chalkley, ‘‘Low atomic-number dye systemfor ionizing radiation measurement,’’ Phon. Sci. Eng.9, 159–166~1965!.

19W. L. McLaughlin, J. C. Humphreys, M. Farahani, and A. Miller, ‘‘Thmeasurement of high doses near metal and ceramic interfaces,’’ inHighDose Dosimetry, Proceedings of International Symposium, Vienna, 19STI/PUB/671~International Atomic Energy Agency, Vienna, 1985!, pp.109–133.

20A. M. Mattson, C. O. Jensen, and R. A. Dutcher, ‘‘Triphenyltetrazoliuchloride as a dye for vital tissue,’’ Science106, 294–296~1947!.

21F. H. Strodss, N. D. Cherionis, and E. Strodss, ‘‘Demonstration of reding enzyme systems in neoplasms and living mammalian tissues byphenyltetrazolium chloride,’’ Science108, 113–115~1948!.

22F. P. Altman, ‘‘Review: Tetrazolium salts and formazans,’’ Prog. Htochem. Cytochem.9, 51–88~1976!.

23Z. S. Gierlach and A. T. Krebs, ‘‘Radiation effects on 2,3,triphenyltetrazolium chloride solutions,’’ Am. J. Roentgenol. RadiuTher.62, 559–563~1949!.

24A. T. Krebs, ‘‘Dosimeters: Recent developments,’’The Encyclopedia ofX-Rays and Gamma Rays, edited by G. L. Clark~Reinhold, New York,1963!, pp. 274–276.

25J. I. Zweig, M. L. Herz, W. L. McLaughlin, and V. Bhuthimethee, ‘‘Druactivation by gamma irradiation: A new direction for molecular desigIn-vitro and in-vivo studies of a substituted polyaminoaryl nitrile,’’ Cacer Treatment Rep.61, 419–423~1977!.

26D. F. Lewis, ‘‘A processless electron recording medium,’’ElectronicImaging, Proceedings of SPSE’86 Symposium, Arlington, VA, 1986~So-ciety for Imaging Science and Technology, Springfield, VA, 1986!, pp.76–79.

27M. C. Saylor, T. T. Tamargo, W. L. McLaughlin, H. M. Khan, D. FLewis, and R. D. Schenfele, ‘‘A thin film recording medium for use


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food irradiation,’’ @Radiat. Phys. Chem.31, 529–536~1988!#.28W. L. McLaughlin, Y. D. Chen, C. G. Soares, A. Miller, G. Van Dyke

and D. F. Lewis, ‘‘Sensitometry of the response of a new radiochrofilm dosimeter to gamma radiation and electron beams,’’ Nucl. InstruMethods Phys. Res. A302, 165–176~1991!.

29M. Farahani, F. C. Eichmiller, and W. L. McLaughlin, ‘‘Measurementabsorbed doses near metal and dental material interfaces irradiatedand gamma-ray therapy beams,’’ Phys. Med. Biol.35, 369–385~1990!.

30C. G. Soares, ‘‘Calibration of ophthalmic applicators at NIST: A revisapproach,’’ Med. Phys.18, 787–793~1991!.

31C. G. Soares and W. L. McLaughlin, ‘‘Measurement of radial dose dtributions around small beta-particle emitters using high-resolution rachromic foil dosimetry,’’ in Solid State Dosimetry, Proceedings of theTenth International Conference, Washington, DC, 1992, edited by EGoldfinch, S. W. S. McKeever, and A. Scharmann@Radiat. Prot. Dosim.48, 367–372~1993!#.

32M. Farahani, F. C. Eichmiller, and W. L. McLaughlin, ‘‘A new methofor shielding electron beams used for head and neck cancer treatmMed. Phys.20, 1237–1241~1993!.

33W. L. McLaughlin, M. Al-Sheikhly, D. F. Lewis, A. Kova´cs, and L.Wojnarovits, ‘‘A radiochromic solid-state polymerization reaction,’’ invited paper inPolymer Preprints, 35, Proceedings of the Symposium oRadiation Effects on Polymers, Washington, DC, 1994, edited by RClough ~unpublished!, pp. 920–921.

34W. L. McLaughlin, M. Al-Sheikhly, D. F. Lewis, A. Kova´cs, and L.Wojnarovits, ‘‘Radiochromic solid-state polymerization reaction,’’ in Irradiation of Polymers, edited by R. L. Clough and S. W. Shalaby~Ameri-can Chemical Society, Washington, DC, 1996!, pp. 152–166.

35W. L. McLaughlin, J. M. Puhl, Al-Sheikhly, C. A. Christou, A. Miller, A.Kovacs, L. Wojnarovits, and D. F. Lewis, ‘‘Novel radiochromic films forclinical dosimetry,’’ inProceedings of the 11th International Conferencon Solid State Dosimetry, II, Budapest, July, 1995, edited by A. Peto anG. Uchrin @Radiat. Prot. Dosim.66, 263–268~1996!#.

36Y. Zhu, A. S. Kirov, V. Mishra, A. S. Meigooni, and J. F. Williamson‘‘Quantitative evaluation of radiochromic film response for twodimensional dosimetry, Med. Phys.24, 223–231~1997!.

37I. Janovsky and K. Mehta, ‘‘The effects of humidity on the responseradiochromic dosimeters FWT-60-00 and GafChromic DM-1260,’’ Rdiat. Phys. Chem.43, 407–409~1994!.

38W. L. McLaughlin, C. G. Soares, J. A. Sayeg, E. C. McCullough, R.Kline, A. Wu, and A. H. Maitz, ‘‘The use of a radiochromic detector fothe determination of stereotactic radiosurgery dose characteristics,’’ MPhys.21, 379–388~1994!.

39P. T. Muench, A. S. Meigooni, R. Nath, and W. L. McLaughlin, ‘‘Photoenergy dependence of the sensitivity of radiochromic film comparedsilver halide film and lithium fluoride TLDs,’’ Med. Phys.18, 769–775~1991!.

40W. L. McLaughlin and M. M. Kosanic, ‘‘The gamma-ray responsepararosaniline cyanide dosimeter solutions,’’ Int. J. Appl. Radiat. Isot.25,249–262~1974!.

41B. B. Radak, M. M. Kosanic, M. B. Sesic, and W. L. McLaughlin, ‘‘Acalorimetric approach to the calibration of liquid dose meters in higintensity electron beams,’’ inBiomedical Dosimetry, STI/PUB/401~In-ternational Atomic Energy Agency, Vienna, 1975!, pp. 633–641.

42W. L. McLaughlin, M. M. Kosanic, V. M. Markovic, M. T. Nenadovic,K. Sehested, and J. Holcman, ‘‘The kinetics of dye formation by puradiolysis of pararosaniline cyanide in aqueous or organic solution,’’ R”

Report No. M-2022, Riso” National Laboratory, Roskilde Denmark, 197943K. Bobrowski, G. Dzierz´howska, J. Grodkowski, Z. Stuglik, Z. P. Zago´r-

ski, and W. L. McLaughlin, ‘‘A pulse radiolysis study of the leucocyanide of malachite green dye in organic solvents,’’ J. Phys. Chem.89,4358–4366~1985!.

44A. Kovacs, L. Wojnarovits, W. L. McLaughlin, S. E. Ebrahim Eid, and AMiller, ‘‘Radiation-chemical reaction of 2,3,5-triphenyl-tetrazolium chloride in liquid and solid state,’’Proceedings of the Eighth Tihany Confeence on Radiation Chemistry, August 1994, edited by G. Fo¨ldiak, J.Dobo, and R. Schiller@ Radiat. Phys. Chem.47, 483–486~1996!#.

45A. Kovacs, L. Wojnarovits, N. B. El-Assy, H. Y. Afeefy, M. Al-Sheikhly,M. L. Walker, and W. L. McLaughlin, ‘‘Alcohol solutions of triphenyl-tetrazolium chloride as high-dose radiochromic dosimeters,’’Proceedingsof the Ninth International Meeting on Radiation Processing II, IstanbSeptember 1994, edited by O. Jrven@Radiat. Phys. Chem.46, 1217–1225~1995!#.

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46W. L. McLaughlin, ‘‘Solid-phase chemical dosimeters,’’ inSterilizationby Ionizing Radiation, edited by E. R. L. Godghran and A. J. Goud~Multiscience, Montreal, 1974!, Vol. I, pp 219–324.

47W. L. McLaughlin, A. Miller, S. Fidan, K. Pejtersen, and W. B. Pederso‘‘Radiochromic plastic films for accurate measurement of radiationsorbed dose and dose distributions,’’ Radiat. Phys. Chem.10, 119–127~1977!.

48International Specialty Products~private communication!.49J. C. Humphreys and W. L. McLaughlin, ‘‘Dye film dosimetry for radia

tion processing,’’ IEEE Trans. Nucl. Sci.NS-28, 1797–1801~1981!.50N. V. Klassen, L. van der Zwan, and J. Cygler, ‘‘GafChromic MD-5

Investigated as a precision dosimeter,’’ Med. Phys.24, 1924–1934~1997!.

51W. L. McLaughlin, J. C. Humphreys, B. B. Radak, A. Miller, and T. AOlejnik, ‘‘The response of plastic dosimeters to gamma rays and electat high absorbed dose rates,’’ Radiat. Phys. Chem.14, 535–550~1979!.

52S. V. Nablo and E. P. Tripp, ‘‘Low energy electron process applitions,’’ Radiat. Phys. Chem.9, 325–352~1977!.

53R. M. Uribe, M. Barcelo, W. L. McLaughlin, A. E. Beunfil, and J. Rio‘‘Initial color development in radiochromic dye films after a short intenpulse of accelerated electrons,’’ Radiat. Phys. Chem.35, 724–727~1990!.

54See Ref. 46.55V. Danchenko, G. F. Griffen, and S. S. Brashears, ‘‘Delayed darkenin

radiation exposed radiochromic dye dosimeters,’’ IEEE Trans. Nucl.NS-28, 4156–4160~1981!.

56R. D. H. Chu, G. VanDyk, D. F. Lewis, K. P. J. O’Hara, B. W. Bucklanand F. Dinelle, ‘‘GafChromic dosimetry media: A new high dose thfilm routine dosimeter and dose mapping tool,’’ Radiat. Phys. Chem.35,767–773~1990!.

57L. E. Reinstein and G. R. Gluckman, ‘‘Predicting optical densitomeresponse as a function of light source characteristics for radiochromicdosimetry,’’ Med. Phys.24, 1935–1942~1997!.

58Sou-T. Chiu-Tsao, A. de la Zerda, J. Lin, and J. Ho Kim, ‘‘High sentivity GafChromic film dosimetry for125I seed,’’ Med. Phys.21, 651–657~1994!.

59A. S. Meigooni, M. S. Sanders, G. S. Ibbott, and Szeglin, ‘‘Dosimecharacteristics of improved radiochromic film,’’ Med. Phys.23, 1883–1888 ~1996!.

60J. A. Sayeg, C. W. Coffey, and W. L. McLaughlin, ‘‘The energy responof GafChromic radiation detector,’’ Med. Phys.17, 521 ~1990!. ~Ab-stract!

61J. A. Sayeg and R. C. Gregory, ‘‘A new method for characterizing beray ophthalmic applicator sources,’’ Med. Phys.18, 453–461~1991!.

62R. Tanaka, S. Mitome, and N. Tamura, ‘‘Effects of temperature, relahumidity and dose rate on the sensitivity of cellulose triacetate dosimeto electrons and gamma rays,’’ Int. J. Appl. Radiat. Isot.35, 875–881~1981!.

63W. L. McLaughlin, ‘‘The measurement of absorbed dose and dose grents,’’ Radiat. Phys. Chem.15, 9–38~1980!.

64W. L. McLaughlin, A. W. Boyd, K. H. Chadwick, J. C. McDonald, anA. Miller, Dosimetry for Radiation Processing~Taylor and Francis, Lon-don, 1989!.

65L. E. Reinstein, G. R. Gluckman, and A. G. Meek, ‘‘A rapid color stablization technique for radiochromic film dosimetry,’’ Phys. Med. Biol.43,2703–2708~1998!.

66M. L. Walker, J. M. Puhl, C. G. Soares, J. C. Humphreys, B. M. Coursand W. L. McLaughlin, ‘‘Precision source profiling techniques for ioniing radiation sources,’’ Proceedings RadTech,Radiation Curing Confer-ence 1992~unpublished!, pp. 614–625.

67A. Miller, E. Bjergbakke, and W. L. McLaughlin, ‘‘Some limitations inthe use of plastic and dyed plastic dosimeters,’’ Int. J. Appl. Radiat. I26, 611–620~1975!.

68R. Ramani, A. W. Lighthouse, D. L. D. Mason, and P. F. O’Brien, ‘‘Thuse of radiochromic film in treatment verification of dynamic stereotaradiosurgery,’’ Med. Phys.21, 389–392~1994!.

69A. Niroomand-Rad, S. T. Chiuo-Tsao, C. G. Soares, A. S. Meigooni,A. Korov, ‘‘Comparison of uniformity of dose response of double layradioelectronic films~MD-55-2! measured at 5 institutions,’’ Med. Phys~submitted!.

70L. E. Reinstein, ‘‘Eliminating interference fringe artifacts in scanniHe–Ne laser film densitometry,’’ Med. Phys.22, 1011~1995!. ~Abstract!

71R. Mavrodineanu and J. R. Baldwin,Metal-On-Quartz Filters as a Stan


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dard Reference Material for Spectrophotometry, NBS Spec. Publ. 260-68~USGPO, Washington, DC, 1980!.

72A. Sliski, Photo-electron Corporation~private communication!.73S. Goetsch, ‘‘Calibration of Sr-90 ophthalmic applicators,’’ Int. J. Radi

Oncol., Biol., Phys.16, 1653~1989!.74C. G. Soares, ‘‘Comparison of NIST and manufacturing calibrations

90Sr190Y ophthalmic applicators,’’ Med. Phys.22, 1487–1493~1995!.75C. G. Soares, ‘‘A method for the calibration of concave90Sr190Y Oph-

thalmic Applicators,’’ Phys. Med. Biol.37, 1005–1007~1992!.76S. M. Vatnitsky, ‘‘Radiochromic film dosimetry for clinical proton

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polysiloxane shields for radiation therapy of maxillo-facial tumorsMed. Phys.18, 273–278~1991!.

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radiochromic ﬁlm dosimetry: recommendations of …lcr.uerj.br/manual_abfm/radiochromic film...

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