Practical exercise: Practical exercise: Effective dose estimate Effective dose estimate

in CTin CTTRAINING COURCE PROGRAM TRAINING COURCE PROGRAM 19 – 20 May 2011, Sofia, Bulgaria19 – 20 May 2011, Sofia, Bulgaria

Virginia TsapakiVirginia TsapakiMedical Physics DptMedical Physics Dpt

Konstantopoulio General HospitalKonstantopoulio General Hospitalemail: virginia@otenet.gremail: virginia@otenet.gr

Dose DataMed1 projectDose DataMed1 project

““In order to assess population exposures from In order to assess population exposures from medical radiology in terms of the collective or per medical radiology in terms of the collective or per caput effective dose it is necessary to estimate caput effective dose it is necessary to estimate representative mean effective doses (E), for each representative mean effective doses (E), for each type of x-ray examination that makes a significant type of x-ray examination that makes a significant contribution to the collective dose in a country”contribution to the collective dose in a country”

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CT exams in the TOP20 list of the

report 154

CT headCT neckCT chestCT spineCT abdomenCT pelvisCT trunk

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focused to organ of interest

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Summary of Dose MetricsSummary of Dose Metrics Air doseAir dose

CTDI – CT Dose IndexCTDI – CT Dose Index

DLP DLP

Organ Dose Organ Dose

Effective DoseEffective Dose

Slice Plane

RotationAxis

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CT Dose Index in multislice CTCT Dose Index in multislice CT

CTDIvol = CTDIw / pitch

CTDIvol was introduced to allow for variations in exposure in the z direction when the pitch

was not equal to one

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)_( lengthExposureCTDIDLP vol ×=

100 mGyCm = 10 mGy CTDI × 10 cm 300 mGyCm = 10 mGy CTDI × 30 cm

Dose Length Product (DLP)Dose Length Product (DLP)

Dose in one rotation x exposure length (mGycm)

DLP : A convenient index for total dose

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E = Σ wT.HT

E : effective doseE : effective dose wT : weighting factor for organ or tissue T : weighting factor for organ or tissue T

HT : equivalent dose in organ or tissue T : equivalent dose in organ or tissue T

The The EE, is defined in ICRP 60 [ICRP, 1991], ICRP 103 [ICRP, , is defined in ICRP 60 [ICRP, 1991], ICRP 103 [ICRP, 2007b] and ICRU 51 [ICRU, 1993]. 2007b] and ICRU 51 [ICRU, 1993].

It is the sum over all the organs and tissues of the body of It is the sum over all the organs and tissues of the body of the product of the equivalent dose, the product of the equivalent dose, HHTT, to the organ or , to the organ or tissue and a tissue weighting factor, tissue and a tissue weighting factor, wwTT, for that organ or , for that organ or tissuetissue

Effective dose (E)Effective dose (E)

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Effective doseEffective dose

Calculation from organ dosesCalculation from organ doses

Calculation from DLP using conversion Calculation from DLP using conversion factors.factors.

(European Guidelines)(European Guidelines)

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CTDI pencil chamber method

A specially designed ion chamber with a shape of a pencil.

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)_( lengthExposureCTDIDLP vol ×=

100 mGyCm = 10 mGy CTDI × 10 cm 300 mGyCm = 10 mGy CTDI × 30 cm

Dose Length Product (DLP)Dose Length Product (DLP)

Dose in one rotation x exposure length (mGycm)

DLP : A convenient index for total dose

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A first order effective dose estimate(for mean population dose purposes)

DLPEE DLP ×=

EUR16262 Guidelines on Quality Criteria for CT(http://www.drs.dk/guidelines/ct/quality)

Region of Body E/DLP Conversion Factor mSv.mGy-1.cm-1

Head 0.0023 Neck 0.0054 Chest 0.017 Abdomen 0.015 Pelvis 0.019

European Guidelines for Multislice Computed European Guidelines for Multislice Computed Tomography Tomography

ttp://www.msct.info/CT_Quality_Criteria.htmttp://www.msct.info/CT_Quality_Criteria.htm..

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The document includes both adult and paediatric The document includes both adult and paediatric conversions coefficientsconversions coefficients

Important for paediatric examsImportant for paediatric exams

When using conversion coefficients for children When using conversion coefficients for children one must be aware that these coefficients have one must be aware that these coefficients have been obtained for a 16 cm CT dose phantom, been obtained for a 16 cm CT dose phantom, whereas the CT console indicator will provide DLP whereas the CT console indicator will provide DLP or CTDI assuming the use of the 32-cm diameter or CTDI assuming the use of the 32-cm diameter body phantom. body phantom.

In pediatric examinations, the figures displayed in In pediatric examinations, the figures displayed in the CT console should be multiplied by a factor of the CT console should be multiplied by a factor of 2 for children and of 3 for infants in order to give 2 for children and of 3 for infants in order to give a realistic estimate of the patient's dose.a realistic estimate of the patient's dose.

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Organ doses NRPB

GSF

Jones DG and Shrimpton P Nomalised Organ Doses for x-ray computed tomography calculated using Monte Carlo techniques NRPB SR 250 NRPB Chilton Oxon 1993

Zankl M, Panzer W and Drexler G The Calculation of Dose from External Photon Exposures using Reference Human Phantoms and Monte Carlo Methods Part IV: Organ Doses from CT Examinations GSF-Bericht 30/91 GSF-Forschungszentrum fur Umwelt und Gesundheit, Institut fur Strahlenschutz, Neuherberg, Germany 1991

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Anthropomorphic phantoms (Rando phantom):TLDs placed in specific positions in the phantom for organ dose measurement

Organ doses

Software methods Software methods

CT-Expo [www.sascrad.com]CT-Expo [www.sascrad.com]

ImPACT CT Patient Dosimetry ImPACT CT Patient Dosimetry Calculator (www.impactscan.org)Calculator (www.impactscan.org)

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2020

Introduction Provides an introduction and instructions for use

Scan Calculation The data entry and results sheet

Paediatric Information on relative doses to adult and paediatric patients

Phantom Allows interactive selection of the scan range used for dose calculation using a diagram of the phantom used to generate SR250

Scanners Provides data on CT scanner models, including CTDI in air and phantom, as well as the scanner matching data

MatchData Gives data required to perform the scanner matchings in the Scanners worksheet

Collimation Lists relative CTDI values at different collimations for a range of CT scanners. These values are more useful for multi-slice scanners, as the CTDI can vary considerably over the range of available collimations

MonteCarloData Contains the unformatted SR250 data set.

Doses Contains the formatted dose data from the SR250 data set that is currently loaded.

DoseCalculations Performs the organ dose calculations, and calculation of remainder organ doses etc.

Selections Provides data for the drop down selection boxes in the ScanCalculation worksheet, and performs calculations for 'remainder' organ doses

Version Details changes made in each version, from version 0.99e onwards

IntroductionThis spreadsheet is a tool for calculating patient organ and effective doses from CT scanner examinations. It makes use of the NRPB Monte Carlo dose data sets produced in report SR250 (link at bottom of page). SR250 provides normalised organ dose data for irradiation of a mathematical phantom by a range of CT scanners.As SR250 was produced in 1993, it does not include data for more modern scanners. To overcome this problem, the ImPACT CT scanner dose survey was carried out by physicists in the UK and Europe.

This work, provides a method for 'matching' the dose distribution of newer scanners to scanners included in SR250. The matching results are included in this spreadsheet. As new scanners are introduced, their matches will be included in updates to this spreadsheet. More details can be found on the dose survey page on the ImPACT website (link below)

Installation

Installation is fairly simple, and only requires the SR250 data sets (MCSET01.DAT to MCSET23.DAT) to be present in the same directory as this spreadsheet. (SR250 is sold by the NRPB - see link below)

Macros are used on this spreadsheet for a variety of purposes. Depending on your version of Excel , and macro options, the security level may have to be switched to 'medium' (select 'Tools' -> 'Options' -> 'Security' -> 'Macro Security'), and/or ImPACT added to your trusted Macro sources.

The results produced by the CTDosimetry spreadsheets have been checked against those produced by CTDOSE, produced by John Le Heron, the standard software used to calculate doses from the NRPB SR250 datasets. The two methods produce identical results for a range of scans and scanners, with the exception of small differences between the doses calculated for muscle and for the 'remainder' organs. These differences are present despite an apparent similarity in calculation method, and are typically 1-2%.

This spreadsheet has been checked for macro viruses, and the logic and calculations been tested extensively, however ImPACT accept no responsibility for loss or damage incurred as a result of its use.

Worksheets

CTDosimetry.xls consists of 12 worksheets

ImPACT CT Patient Dosimetry CalculatorVersion 1.0.3 24/08/2010

The system should work on any PC with Microsoft Excel 2000 or above. It has not yet been tested on a Apple computer, but it is anticipated that it should work on a Mac.

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Manufacturer Select the scanner manufacturer from the drop down list

Scanner Select the scanner model or scanner model group for the drop down list.

kV Choose the appropriate scan kV.

Scan Region Choose head or body.

Tube current The x-ray tube current. Note that this should be the actual scanner mA, and not the 'effective mAs' displayed on some multi-slice scanners

Rotation time The scanner tube rotation time

Spiral pitch The scanning pitch (table travel per rotation/total collimated slice width). For axial scanning, (couch increment)/(collimated slice width) should be used

mAs/rotation The total mAs per gantry rotation. Do not enter data in this box - it is calculated automatically.

Effective mAs The mAs/per rotation divided by the spiral pitch. This is a calculated value that provides a basis for comparison of spiral protocols with different pitches

Collimation The total nominal x-ray beam width along the z-axis, selected from a range of possible values in the drop down box. This determines the relative CTDI compared to the reference (usually 10 mm) collimaiton.

The Monte Carlo data set that is used for this combination of scanner, kV and body part is displayed in the cell marked 'Data Set'. The data set that is currently loaded is displayed below. If these do not match, no dose is calculated. To load the appropriate data set, and enable dose calculation, press the 'Update Data Set' button.

Scan and patient data is entered in the box on the top right of the ScanCalculations worksheet.

The following four selections, made in the top left box on the ScanCalculations worksheet define the Monte Carlo data set that is used:

To calculate doses using CTDosimetry.xls, the user must enter a number of parameters relating to the scanner and the scan series

Using CTDosimetry.xls

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42,5 -1 -10 64 -1 -10

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Zoom InZoom Out

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Scanner Model: Acquisition Parameters:Manufacturer: mA 340 mAScanner: Rotation time 0.8 skV: mAs / Rotation 272 mAsScan Region: Collimation mmData Set MCSET19 Slice Width 10 mmCurrent Data MCSET19 Pitch 1.35Scan range Rel. CTDI 1.26 at selected collimationStart Position -5 cm CTDI (air) 34.5 mGy/100mAsEnd Position 45 cm CTDI (soft tissue) 36.9 mGy/100mAs

Patient Sex: f nCTDIw 12.8 mGy/100mAs

Organ wT HT wT.HT Remainder Organs HT

Gonads 0.2 33.434 6.687 Adrenals 30.370Bone Marrow (red) 0.12 15.854 1.902 Brain 0.006Colon 0.12 32.619 3.914 Upper Large Intestine 35.786Lung 0.12 7.010 0.841 Small Intestine 34.884Stomach 0.12 35.678 4.281 Kidney 38.987Bladder 0.05 39.058 1.953 Pancreas 30.545Breast 0.05 1.498 0.075 Spleen 33.313Liver 0.05 33.378 1.669 Thymus 1.209Oesophagus (Thymus) 0.05 1.209 0.060 Uterus 35.652Thyroid 0.05 0.100 0.005 Muscle 17.640Skin 0.01 13.381 0.134

Bone Surface 0.01 22.972 0.230 CTDIw (mGy) 34.7

Remainder1 0.025 17.709 0.443 CDTIv ol (mGy) 25.7

Remainder 2 0.025 17.709 0.443 DLP (mGy.cm) 1284.5Total Effective Dose (mSv) 22.637

ImPACT CT Patient Dosimetry Calculatorversion 0.99m, 1/07/2002

Update Data Set

GE

GE QX/i, LightSpeed, LightSpeed Plus

120Body

Look upGet From Phantom Diagram

5

Look up

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2. Scan Range

Scan Range Data (Slice Positions)

1. Age Group Gender Scan Range z Lfrom z- to z+ [cm]

0

3. Scanner Data for Scan Region "Body"

Manufacturer nCTDIw Uref PB,H kCT kOB ∆L

Scanner [mGy/mAs] [kV] [cm]

0,150 130 0,42 0,80 1,00 0,0

-0,0070 3,35 0,00 0,00

4. Select mode

5. Scan Parameters Please Enter Actual Settings:

U I t Qel Q N * hcol TF hrec p Ser.[kV] [mA] [s] [mAs] [mAs] [mm] [mm] [mm]

0 1,0

6. ResultsDose Values per Scan or per Series* Tissue or HT per Series Remainder HT per Series

CTDIw CTDIvol DLPw* E*

Duterus* Organ [mSv] Organs [mSv]

[mGy] [mGy] [mGy*cm] [mSv] [mSv] Thyroid 0,0 Brain 0,0

0,0 0,0 hrec? hrec? n.a. Breasts 0,0 Thymus 0,0

Child/Baby: all CTDI and DLP values refer to 16cm head phantom ! Oesophagus 0,0 Spleen 0,0Lungs 0,0 Pancreas 0,0

Dose Values per Examination Liver 0,0 Adrenals 0,0

DLPw E Duterus Stomach 0,0 Kidneys 0,0

[mGy*cm] [mSv] [mSv] Colon 0,0 Small intest. 0,0

Ser? Ser? n.a. Testicles 0,0 Upp. large int. 0,0

Effective dose E refers to ICRP 60 Ovaries 0,0 Uterus 0,0Please note: Bladder 0,0All organ doses HT are based on conversion coeff icients for stand- Bone marrow 0,0 Misc. HT per Seriesard patients (ADAM, EVA, CHILD, BABY) and serve for information Bone surface 0,0 [mSv]

purposes only (in particular organs outside the scan range) ! Skin 0,0 Eye lenses 0,0

Scanner Model

Calculate

Adult

Demo

Spiral Scanner

male female

Body mode for head/neck region Spiral mode

Get Values

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Dose Reference Level (DRL) values are Dose Reference Level (DRL) values are reported by various national or international reported by various national or international

organizations for abdomen CTorganizations for abdomen CT

DRL CTDI DLP

Abdomen EUR 16262 SC 1999 35 900

Abdomen EC MDCT 2004 25 524

Abdomen UK SC 2003 20 460

Abdomen UK MDCT 2003 20 470

Abdomen Germany MDCT 2003 24 1500

Abdomen IAEA 2006 10.9 696

Abdomen USA NEXT Survey 30* 740

* Data from USA are not DRL but 75th percent of data distribution. They are put in this table for comparison purposes.

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Table 1. Effective dose in various exams.

Examination Effective dose (mSv)

Abdomen radiography 0.7

Chest or Abdomen CT 8.0

3 phase CT liver study 15.0

CT guided biopsy 23.0

CT guided RF ablation 35.0

Repeated CT guided RF ablation 112.0

CT coronary angiography 10.0

Coronary angiography 8

Thallium heart scan 35

CT urography 14.8

CT colonography 5.1

Neonatal abdomen CT 13.1

1 year old abdomen CT 11.1

Annual natural background radiation 2.0

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Thank you for Thank you for your attentionyour attention