Inr. J. Rucfkrion Onco/ogv Biol. fhys., Vol. IO, Sup. I. pp. W-103 Printed in the U.S.A. All rights reserved.

031%3016/X4/$3.00 + .OO Copyright B 1984 Pergamon Press Ltd.

??Session IV: Suggested Guidelines

TELETHERAPY EQUIPMENT AND SIMULATORS

CARLOS E. DE ALMEIDA, PH.D. ANDEUGENIO R. CECATTI,M.SC.

Instituto de Radioprote@o e Dosimetria, CNEN, Caixa Postal 37025,, 22602, Rio de Janeiro, RJ, Brazil

A comprehensive Quality Assurance program in a radiation therapy center is desirable regardless of its size, and should cover among others the following areas: physical parameters of the therapy machines, dosimetric standards, preventive maintenance of radiation emitting sources and measuring instruments. In a radiation therapy center, regardless of its size and patient load, it is advisable to have a quality assurance program covering all the treatment planning steps. The following areas should be taken into consideration: physical parameters of the machines; dosimetric standards; radiation safety procedures and preventive maintenance of irradiators and radiation measuring instruments. The minimum instrumentation required and the critical parameters to be observed to establish a quality assurance program are discussed; the suggestions are applica- ble to the various sizes of radiation therapy centers. It is essential that all the procedures and results obtained are well documented and a critical evaluation of the program be performed periodically. The procedures and frequency suggested are applicable to low, medium and high energy treatment machines and simulators. The fluctuation on physical parameters currently observed in clinical physics practice strongly supports the efforts and costs of a quality assurance program.

Quality assurance, Therapeutical equipment, Dosimetric equipment.

INTRODUCTION

Modern radiotherapy is presently using, in some sit- uations, rather sophisticated machines demanding a better control of the clinical and physical parameters that might influence the final clinical results. It is already known that in some cases a variation of a few percent in the expected delivered dose may be con- nected with the failure of a treatment, or to the occur- rence of undesirable complications.

In a radiation therapy center, regardless of its size and patient load, it is advisable to have a comprehen- sive quality assurance program covering all the treat- ment planning steps. The following areas should be taken into consideration: physical parameters of the machines; dosimetric standards; radiation safety proce- dures and preventive maintenance of irradiators and radiation measuring instruments3

The two major goals to be achieved are: a) the establishment and maintenance of an optimum criteria for machine performance in order to assure the desir- able degree of precision in the dose delivery and b) the minimization of machine down-time.

METHODSANDMATERIALS

The quality assurance program consists of periodical selected tests to evaluate the performance of the instru- mentation within the preestablished operational limits. In addition, the data bank will indicate the need for change in design of a particular component as well as to which parameters one should devote more attention.

Radiation therapy centers differ with respect to staff skill, therapeutical and dosimetric equipment. There- fore it would be unrealistic to just lay guidelines before identifying the differences that define small, medium and large centers. Presented in Table 1 are the facilities that one may expect to have in the different classes of centers, even though it is realized that this is an approximation, since the determining economical, social and health factors related to patient load are not the same for all countries.

It is rather tempting to treat the quality assurance program as a whole, due to large number of related problems, i.e., treatment planning, personnel, dosimetric methods and instrumentation. However the scope of this paper must be restricted to teletherapy equipment

Accepted for publication 23 November 83.

99

100 Radiation Oncology 0 Biology 0 Physics 1984, Volume 10, Supplement 1

Table 1. Basic facilities required for normal operation of a radiation center

Basic facilities required for normal operation Small Medium Large

1. Treatment equipment Superficial therapy equipment Orthovoltage therapy equipment Fixed cobalt unit Beta applicators Brachytherapy sources Simulator Rotational cobalt unit or low energy accelerator* Medium energy accelerator? High energy acceleratort

2. Dosimetry equipment Field ionization dosimetry system Small water phantom with a hole that fits the ionization chamber Radiation survey meter Parallel plate ionization chamber Soft chamber Solid plastic phantom Dosimetric film Water phantom tank Manual densitometer Reference ionization dosimetry system Automatic densitometer Automatic isodose plotter Radiotherapy planning system

0 X X X X X X 8 X X X X

§ X X 8 X

§ X X

X

X X X X X X X X X

X X X X X X X X X X X §

X X X X

QOptional. *4 or 6 MV photon unit without electron therapy. tPhoton beam of 8 or 10 MV and electron therapy capability with energies up to about I2 MeV. $Photon beam above 15 MV and electrons with energies up to 45 MeV.

and simulators. Therefore a general guideline is pro- posed in Table 2, gi;/ing the minimum and ideal fre- quencies for data assessment as a basis for the design of a particular situation.

The execution of this program is based on the follow- ing premises: 1. staff appreciation for its need; 2. avail- ability of adequately trained manpower; 3. appropriate radiation measuring instruments; 4. eagerness for im- provement of the methodological procedures; and 5. constant search for the true value of the dose delivered to a patient.

RESULTS

The establishment of a comprehensive quality assur- ance program for teletherapy machines requires a sim- plified data assessment methodology in order to avoid unnecessary paper work. Figure 1 shows one example of a data sheet for a cobalt machine-Eldorado type with some typical results.2

Figures 2 and 3 present the results of calibration factors for high energy photon and electron beams performed during 30 consecutive days of operation.

Initially for this case, two daily calibrations were per- formed after the machine being commissioned. An acceptable variation of &3% for the reference value was adopted and a required change would be made when:

1. a constant displacement greater than &3% is ob- servable for three consecutive days; the patient charts would then be adjusted.

2. a definite trend would be observable even within the pre-set limits which generally implies a fine adjust- ment of the reference factors.

It was necessary to change the reference factors reasonably often, over the two years of observation, for all energies, although the change in factor for one energy did not imply in change for the others

CONCLUSIONS

The success of this program is based on the persis- tent staff attitude during the data aquisition period and the staff ability for data analysis.

Typical center size

Equipment and simulators 0 C.E.DE ALMEIDA AND E.R. CECATTI

Table 2. Quality assurance program for therapy equipment and simulators

101

Frequency

Checks Minimal Ideal References

5.

Simulator Audible alarms, emergency stop buttons, collision strips and stretcher lock Weekly Daily Couch motions, collimator X, k and rotation,

delineator X and Y, and arm rotation Collimator and delineator alignment Optical distance indicator Field scales Integrity of the accessories Image quality constancy Beam penetrative quality Gear boxes and arm rotation worm gear Focus size

Weekly Daily 5 Monthly Weekly 5 Monthly Weekly 5 Monthly Weekly 5 Biannually Monthly 5 Biannually Monthly 5 Biannually Monthly 5 Annually Biannually 5 Annually Biannually 5

Superficial therapy unit Safety devices Mechanical and electrical systems Dose rate for all qualities Accuracy, precision and linearity of the timer Integrity of the accessories

Monthly Weekly 4, 7 Monthly Weekly 4, 7 Monthly Weekly 4, 7 Annually Biannually 4, 7 Annually Biannually 4

Orthovoltage therapy unit Safety devices, emergency stop buttons and mechanical problems Patient monitoring and communication devices Output determination for all qualities used Half value layer determination for all qualities used Output determination for all cones and qualities used Field symmetry and flatness

Monthly Weekly 4, 7 Weekly Daily 7 Monthly Weekly 4, 7 Quarterly Monthly 4, 7 Two years Annually 4, 7 Monthly Weekly 4, 7

Cobalt unit Machine panel, hand control reading and indicator lights Weekly Daily 4, 7 Patient monitoring and communication devices Weekly Daily 4, 7 Mechanical and electrical safety systems Weekly Daily 4, 7 Integrity of the accessories Monthly Weekly 4, 7 Field symmetry and flatness Quarterly Monthly 7 Radiation field, light field and collimator dial settings coincidence Monthly Weekly 7 Cross hairs alignment Monthly Weekly 7 Treatment couch isocenter Biannually Monthly 4, 7 SSD/SAD readout devices Quarterly Monthly 7 Dose rate determination and coincidence with the decay correction Quarterly Monthly 4, 7 Isocenter of radiation beam Annually Biannually 4, 7 Timer error determination Annually Biannually 4, 7 Determination of the effective source position Two years Annually 7

Linear accelerator units Machine panel, hand control reading and indicator lights Patient monitoring and communication devices Mechanical and electrical safety systems Absorbed dose calibration Integrity of the accessories Energy constancy Field symmetry and flatness Radiation field, light field and collimator dial settings coincidence Cross hairs alignment Treatment couch isocenter SSD/SAD readout devices Optical backpointer and sagittal lights Isocenter of radiation beam Field size dependence Determination of the effective source position

Weekly Daily 1, 4, 7 Weekly Daily 7 Weekly Daily 4, 7 Weekly Daily 1, 4, 6, 7 Monthly Weekly 7 Monthly Weekly 1, 6 Monthly Weekly 1, 6, 7 Monthly Weekly 1, 6 Monthly Weekly 1 Biannually Monthly 1, 4, 7 Quarterly Monthly 1, 7 Monthly Weekly 1 Annually Biannually 1, 4, 7 Two years Annually I, 7 Two years Annually 7

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102 Radiation Oncology 0 Biology 0 Physics 1984, Volume 10, Supplement 1

COBALT UNIT PERIOD: A?RiL/*

Fig. 1. Monthly log sheet used for data recording.

25 MV PHOTON BEAM _--__---____-----__~-+--,_’

+ 0

FIELD SIZE : IO x IO cm2 SSD : 100 cm

DEPTH : 4.0 G*crnm2

0 EARLY MORNING

+ MID-DAY

c3 I I I 1 I I 1 0 5 IO I5 20 25 30

TIME (DAYS)

Fig. 2. Typical calibration factor performance of a 25 Mv photon beam observed during one month.

t

I3 MeV ELECTRON BEAM 1.03 -- ______ ---_-_--_+ ___-___ _-

0 0 0 + 0 0

t t ,‘Q t+ +.

0 + + + 0

k a 1 0.97 ______--_--_-_------ m 3 a 0

FIELD SIZE : IO x IO cm2 SSD : 91.5 cm DEPTH : 3.2 G*cm-’

0 EARLY MORNING

+ MID-DAY 1 I I 1 I I

0 5 IO I5 20 25 30 TIME (DAYS)

Fig. 3. Typical calibration factor performance of a 13 MeV electron beam observed during one month.

Equipment and simulators 0 C.E. DE ALMEIDA AND E.R. CECATTI 103

The results of the program are generally noticed from the beginning for individual cases but its impor- tance will only be appreciated over a long period of time with the reduction of treatment failure, treatment

complications and machine down time. The observed fluctuation of critical parameters during normal opera- tion strongly supports the efforts and costs of a quality assurance program.

REFERENCES

1. AAPM. American Association of Physicists in Medicine: Code of practice for x-ray therapy linear accelerator. Med.

2. de Almeida, C.E., Sibata, C.H., Cecatti, E.R., Kawa- Phys. 2: 110, 1975.

kami, N.S., Alexandre, A.C. and Chiavegatti Jr., M.: Programa de controle de qualidade dos pargmetros fisicos em aparelhos de radioterapia. Radio/. Brasileira 15: 160, 1982.

3. de Almeida, C.E., Sibata, C.H., Cecatti, E.R., Kawa- kami, N.S., Alexandre, A.C. and Petropoulea, C.O.: Quality control program for radiotherapy treatment plan- ning calculations. Proceedings of the 13th World Congress on Medical Physics and Biomedical Engineering, Ham- burg, 1982.

4. Massey, J.B.: Manual of dosimetry in radiotherapy, IAEA

5. McCullough, E.C. and Earle, J.D.: The selection, accep-

Technical Report No. 110 (International Atomic Energy

tance testing, and quality control of radiotherapy treat-

Agency, Vienna), 1970.

ment simulators. Radiology 131: 221, 1979. 6. NACP. Nordic Association of Clinical Physics: Proce-

dures in radiation therapy dosimetry with electron and photon beams with maximum energies between 1 MeV and 50 MeV. Acta Radiol. Oncol. 19: 55, 1980.

7. NCRP. National Council on Radiation Protection and Measurements: Dosimetry of x-ray and gamma-ray beams for radiation therapy in the energy range 10 keV to 50 MeV, NCRP Report No. 69, Washington, 1981.