Journal of the ICRU Vol 5 No 2 (2005) Report 74 Oxford University Press
doi:10.1093/jicru/ndi032
APPENDIX D: REPORTS PRODUCED BY THE HEALTH PROTECTION AGENCY (HPA) (FORMERLY NATIONAL RADIOLOGICAL PROTECTION BOARD, NRPB) GENERAL DESCRIPTION
NRPB has produced three sets of reports that permit estimation of the mean absorbed doses to 25 different tissues and organs in reference adult and paediatric patients from common radiographic, fluoroscopic, and CT examinations. The three sets of reports deal with the following. 1. Common Adult X-ray Examinations 2. Common Paediatric X-ray Examinations 3. Adult Computedtomography Examinations
(NRPB-R262, NRPB-SR262, Hart et al., 1994a,b) (NRPB-R279, NRPB-SR279, Hart et al., 1996a,b) (NRPB-R250, NRPB- SR250 Jones and Shrimpton, 1991, 1993)
Each set consists of a pair of NRPB reports, one providing printed tabulations of conversion coefficients for a sample of the available data and the other (the ‘software report’, denoted ‘NRPB-SR . . .’) includes a computer disk containing a complete listing of all the available dose-conversion coefficients. The listing is arranged in a large series of data files, which can be incorporated into suitable computer programs for processing the conversion coefficients in a manner matched to the requirements of the user. Such user-friendly software packages, which calculate organ doses for any combination of x-ray examination parameters specified by the user, are available from the National Radiation Laboratory, Christchurch, New Zealand, for each set of NRPB reports. The dose-conversion coefficients in the software reports relate organ dose DT/mGy to entrance surface air kerma, Ka,e/mGy and to air kerma–area product, PKA/(Gy cm2) for radiographic and fluoroscopic examinations and to CT kerma index
expressed in ICRU muscle tissue, CK,m/mGy for CT examinations. The same basic Monte Carlo code developed at NRPB is used for all three sets of calculations and both adult and paediatric patients are simulated by hermaphrodite mathematical phantoms. The software reports include organ dose-conversion coefficients for a large number of diagnostic radiation qualities or types of CT scanner.
D.2 REPORT NRPB-SR262 (HART ET AL., 1994b): COMMON ADULT X-RAY EXAMINATIONS D.2.1
Main features of calculations
Details of the Monte Carlo code and the mathematical phantom developed at NRPB are described by Jones and Wall (1985). Conversion coefficients relating DT to Ka,e and to PKA were calculated by simulating typical x-ray examination exposure conditions on a hermaphrodite mathematical phantom representing a typical adult patient. Four million photon histories were followed for each x-ray examination field simulated. The phantom was based on Cristy’s adult hermaphrodite phantom (Cristy, 1980) with Kramer’s modified neck region (Kramer et al., 1982), a breast tissue composition of 50 % fat and 50 % water, and with an esophagus. The arms of the phantom, which lie alongside the trunk, were removed when lateral projections through the trunk were simulated.
D.2.2
Scope of the report
Report NRPB-SR262 (Hart et al., 1994b) is a software report, which includes a computer disk containing files of conversion coefficients relating DT to Ka,e and to PKA for the 68 radiographic projection (e.g., Head) and view (e.g., AP) combinations listed below.
Ó International Commission on Radiation Units and Measurements 2005
Downloaded from http://jicru.oxfordjournals.org/ at University of Prince Edward Island on February 21, 2015
D.1
PATIENT DOSIMETRY FOR X RAYS USED IN MEDICAL IMAGING
Heart LAT L and R Heart LAO, RAO Upper stomach AP, PA Stomach RAO, LPO, LAO Stomach AP, PA, Stomach LAT (L) Kidneys AP, PA Lumbar spine LPO, RPO Lumbar spine AP Lumbar spine LAT L and R Left flexure LAO Right flexure RAO
using the conversion coefficients listed in NRPBSR262 is Ka,e or PKA for each radiograph and the corresponding tube voltage and total beam filtration. Organ doses can be estimated for any combination of the 68 radiographic projections and views, using a software package called XDOSE developed at the National Radiation Laboratory, Christchurch, New Zealand. This software processes the data in NRPBSR262 according to the requirements of the user. An example of part of the results produced by this software for a PA chest radiograph and an AP abdominal radiograph with specified exposure factors is shown in Table D.1.
The focus-to-surface distance dFSD, the position of the central axis of the x-ray beam in the phantom, and the x-ray field size at the image receptor and at the mid-plane of the phantom, for all the above radiographic projections are described in the report. The mid-plane field size is also shown diagrammatically on a drawing of the phantom so that the position of the x-ray field in relation to all the modelled organs can be visualized. For each radiographic projection and view, conversion coefficients are tabulated for 40 x-ray spectra, specified by the peak tube voltage and the total beam filtration. Tube voltages range from 50 to 120 kV, in 10 kV steps; and five total beam filtrations of 2, 2.5, 3, 4, and 5 mm Al are included for each tube voltage. The source of the x-ray spectra data for these calculations is an updated (1991) version of the computer program of Iles (1987). This program produces results very similar to that published by the IPEM (1997). In NRPB-SR262 (Hart et al., 1994b) conversion coefficients are given for 26 organs for the 68 radiographic projection and view combinations and 40 x-ray spectra described above. These 26 organs are the following. Adrenals Brain Breasts Eye Lens Gall bladder Heart Kidneys Liver Lower large intestine
D.2.3
Lungs Oesophagus Ovaries Pancreas Active BM Residual tissues (muscle) Skeleton (bone surfaces) Skin Small intestine
Duodenum AP, PA Duodenum RAO, LPO LSJ LAT L and R Abdomen AP, PA Small intestine AP, PA Pelvis/colon AP, PA Colon RAO, LPO, LAO Urinary bladder AP Hip AP L and R Rectum AP, PA Rectum LAT L and R Rectum LPO, RAO
D.2.4
Illustrative calculation
Organ doses DT for chest PA and abdomen AP examinations were calculated using NRPB-SR262 Monte Carlo data (Hart et al., 1994b). The chest PA examination is performed with a tube voltage of 120 kV, a filtration of 3.00 mm Al, and at the reference dFSD. The entrance air kerma Ka,e for the chest examination is 0.16 mGy. The abdomen AP examination is performed with a tube voltage of 85 kV, a filtration of 3.00 mm Al, and at the reference dFSD. The entrance air kerma Ka,e for the abdomen examination is 5.60 mGy. The results of the organ dose calculation are given in Table D.1.
Spleen Stomach Testes Thymus Thyroid Upper large intestine Urinary bladder Uterus
D.3 REPORT NRPB-SR279 (HART ET AL., 1996b): COMMON PAEDIATRIC X-RAY EXAMINATIONS D.3.1
Main features of calculations
Details of the Monte Carlo code developed at NRPB are described by Jones and Wall (1985). Conversion coefficients relating DT to Ka,e and to PKA were calculated by simulating typical x-ray examination exposure conditions on a series of five hermaphrodite mathematical phantoms representing newborn, 1, 5, 10, and 15-year-old patients. Four million photon histories were followed for each xray examination field that was simulated. The
Application of the report
The information required to estimate organ doses from 68 adult radiographic projections and views 88
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Head AP, PA Head LAT L and R Cervical spine AP Cervical spine LAT L and R Throat LAT L and R Shoulder AP L and R Oesophagus RAO, LAO, LPO Thoracic spine AP Thoracic spine LAT L and R Chest AP, PA Chest LAT L and R Heart AP, PA
APPENDIX D Table D.1. Organ doses DT/mGy calculated for chest PA and abdomen AP examinations using NRPB-SR262 Monte Carlo data and the software package XDOSE for the examination conditions given in Section D.2.4. Organ
D.3.2
Report NRPB-SR279 (Hart et al., 1996b) contains files of conversion coefficients relating DT to Ka,e and to PKA for the 18 radiographic projections and views listed below.
DT/mGy Abdomen AP
0.0970 0.0006 0.0197 0.0003 0.0187 0.0238 0.0025 0.0032 0.0006 0.0362 0.0608 0.0419 0.0846 0.0005 0.0453 0.0163 0.0803 0.00 0.0184 0.0108 0.0001 0.0005 0.0490 0.0181 0.0485 0.0274
0.261 0.00 0.0199 0.00 1.95 1.95 1.64 1.98 1.32 0.0675 0.366 1.08 0.0474 1.28 0.872 0.387 0.507 0.243 0.0094 0.0003 2.61 1.67 0.0643 0.531 0.289 0.217
Head AP, PA, LAT Cervical spine AP, PA, LAT Chest AP, PA, LAT
0 1 5 10 15
Weight/ kg
3.47 9.26 19.0 31.9 54.4
Height/ cm
51.5 75.0 109.0 138.6 164.0
Thickness of head/cm
Thickness of trunk/ cm
AP
LAT
AP
LAT
11.6 15.7 18.1 18.8 19.5
9.0 12.3 14.3 14.9 15.5
9.8 13.0 15.0 16.8 19.6
12.7 17.6 22.9 27.8 34.5
Urinary bladder AP, PA
The dFSD, the position of the central axis of the x-ray beam in each phantom, and the x-ray field size at the image receptor, for all the above radiographic projections are described in the report. The field size at the mid-plane of the phantom is also shown diagrammatically on a drawing of each phantom so that the position of the x-ray field in relation to all the modelled organs can be visualized. For each radiographic projection and view, conversion coefficients are tabulated for 72 x-ray spectra, specified by the peak tube voltage and the total beam filtration. Tube voltage ranges from 50 to 120 kV, in 10 kV steps. For each tube voltage nine total beam filtrations are included, the same five as for the previous adult examinations (i.e., 2, 2.5, 3, 4, and 5 mm Al) and a further four involving additional copper filtration that has been recommended for paediatric radiography (EC 1996d), i.e., 2 mm Al þ 0.1 mm Cu; 2 mm Al þ 0.2 mm Cu; 3 mm Al þ 0.1 mm Cu and 3 mm Al þ 0.2 mm Cu. The source of the x-ray spectra data for these calculations is an updated (1991) version of the computer program of Iles (1987). This program produces very similar results to that published by the IPEM (1997). In NRPB-SR279 (Hart et al., 1996b) conversion coefficients for 26 organs are given for the 18 radiographic projections and views and the 72 x-ray spectra described above. These organs are the following.
phantoms were based on Cristy’s hermaphrodite phantoms (Cristy, 1980) and Kramer’s modified neck region (Kramer et al., 1982) was applied to all of them. An esophagus was added to each phantom. A suitable volume of breast tissue was included in each phantom and in the absence of specific information on the fat content of breast tissue in young children, 50 % fat and 50 % water was used as the breast tissue composition for all of the phantoms. The arms of the phantom, which lie alongside the trunk, were removed when lateral projections through the trunk were simulated. The weights and major dimensions of the five paediatric phantoms are shown below. Age/ years
Lumbar spine AP, PA, LAT Abdomen AP, PA Pelvis AP, PA
Adrenals Brain Breasts Eye lens Gall bladder Heart Kidneys Liver Lower large intestine
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Lungs Oesophagus Ovaries Pancreas Active BM Residual tissues (muscle) Skeleton (bone surfaces) Skin Small intestine
Spleen Stomach Testes Thymus Thyroid Upper large intestine Urinary bladder Uterus
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Adrenals Brain Breasts Eye lens Gall bladder Stomach Small intestine Upper large intestine Lower large intestine Heart Kidneys Liver Lungs Ovaries Pancreas Skin Spleen Testes Thymus Thyroid Urinary bladder Uterus Oesophagus Muscle Total bone Active BM
Chest PA
Scope of the report
PATIENT DOSIMETRY FOR X RAYS USED IN MEDICAL IMAGING
D.3.3
D.3.4
Application of the report
D.4 REPORTS NRPB-R250, NRPB-SR250 (JONES AND SHRIMPTON, 1991, 1993): ADULT CT EXAMINATIONS D.4.1
The same Monte Carlo code and adult hermaphrodite mathematical phantom were used as in the calculations for conventional x-ray examinations (see Appendix D.2.1). Only the esophagus was missing from the phantom described in Appendix D.2.1. The arms of the phantom remained alongside the trunk for all simulated CT examinations, as is the usual practice with patients. To simulate the distinct exposure conditions prevailing during CT examinations, the x-ray source was rotated around the long axis of the phantom. Organ doses were determined for the individual irradiation of 208 contiguous 5-mm-thick transverse slabs of the phantom ranging from the top of the head to the top of the legs. A line x-ray source of the same length of each irradiated slab (5 mm) was used, with the photons emitted normally from the source into a fan-shaped beam spanning the width of the phantom. An abrupt cut-off of the x-ray beam at the edges and faces of the fan (i.e., perfect collimation) is a feature of this model. Conversion coefficients were calculated relating the organ doses to the kerma on the axis of rotation of the scanner free-in-air, i.e., with no phantom or patient present. The imperfect collimation of the x-ray beam in the axial direction, which occurs in practice, can lead to a build-up of dose in adjacent scans. However, this is taken account of by measuring the CT kerma index free-in-air, CK, under the exposure conditions, i.e., slice thickness, tube voltage, and tube-current exposure-time product, PIt. The value of CK is then multiplied by the conversion coefficients to estimate the organ doses for the degree of beam collimation achieved by the CT scanner of
Table D.2. Organ doses DT/mGy for child of 1 year calculated for chest PA and abdomen AP examinations using NRPB-SR279 Monte Carlo data and CHILDOSE software for the examination conditions given in Section D.3.4.
Adrenals Brain Breasts Eye lens Gall bladder Stomach Small intestine Upper large intestine Lower large intestine Heart Kidneys Liver Lungs Ovaries Pancreas Skin Spleen Testes Thymus Thyroid Urinary bladder Uterus Oesophagus Muscle Total bone Active BM
DT/mGy for child of 1 year Chest PA
Abdomen AP
0.0215 0.0002 0.0105 0.0002 0.0026 0.0049 0.0008 0.0009 0.0002 0.0144 0.0029 0.0081 0.0311 0.0004 0.0079 0.0063 0.0107 0.00 0.0080 0.0060 0.0001 0.0003 0.0177 0.0068 0.0259 0.0060
0.0796 0.0001 0.0102 0.0002 0.252 0.271 0.211 0.242 0.152 0.0440 0.0796 0.226 0.0390 0.184 0.167 0.0468 0.118 0.0335 0.0065 0.0024 0.264 0.216 0.0508 0.0748 0.0860 0.0274
Main features of calculations
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Organ doses DT for chest PA and abdomen AP examinations were calculated using NRPB-SR279 Monte Carlo data (Hart et al., 1996b) for child of 1 year. The chest PA examination is performed with a tube voltage of 90 kV, a filtration of 2.00 mm Al and of 0.10 mm Cu, and at the reference dFSD. The entrance air kerma Ka,e for the chest examination is 0.05 mGy. The abdomen AP examination is performed with a tube voltage of 90 kV, a filtration of 2.00 mm Al and 0.10 mm Cu, and at the reference dFSD. The entrance air kerma Ka,e for the abdomen examination is 0.40 mGy. The results of the organ dose calculation are given in Table D.2.
The information required to estimate organ doses from 18 paediatric radiographic examinations using the conversion coefficients listed in NRPBSR279 is the Ka,e or the PKA for each radiograph and the corresponding tube voltage and total beam filtration. Organ doses to any of the phantoms representing a newborn, 1, 5, 10, or 15-year-old patient can be estimated for any combination of the 18 radiographic projections, using a software package called CHILDOSE developed at the National Radiation Laboratory, Christchurch, New Zealand. This software processes the data in NRPB-SR279 according to the requirements of the user. An example of part of the results produced by this software for an examination comprising a PA chest radiograph and an AP abdominal radiograph on a 1-year-old child with the specified exposure factors is shown in Table D.2.
Organ
Illustrative calculation
APPENDIX D
D.4.2
Scope of the reports
Calculations have been performed for 23 sets of exposure conditions (i.e., tube voltage, focus-to-axis
Table D.3. Exposure conditions for calculation of normalized organ doses for CT using Monte Carlo techniques according to Jones and Shrimpton (1991, 1993). Monte Carlo data set no.
1 2 3 4 5 6 7 8 9c 10 11 12 13 14 15 16 17 18 19 20c 21c 22c 23c
CT scanner models for which data set is appropriate
Siemens Somatom 2,DR1/2/3 Somatom DRG,DRG1 Somatom DRH,CR,CR512 Picker 1200SX 1200SX GE CT 8800,9000I/II/HP CT 8800,9000I/II/HP CT 9800,9800Quick CT 9800,9800Quick CT MAX CT PACE CGR CE 10000,12000 Philipse Tomoscan 305N,310,350 (GE No. 2, no Cu) Tomoscan 305N,310,350 (GE No. 2, with Cu) Tomoscan 310,350 (GE No.3, no Cu) Tomoscan 310,350 (GE No. 3, with Cu) Tomoscan TX Tomoscan CX,CX/S Tomoscan LX Tomoscan TX Tomoscan TX Tomoscan LX Tomoscan LX
Tube voltage/kV
Focus to axis distance/mm
Flat filter/
Shaped filter/
Al mm
Cu mm
Option
Type
125 125 125
760 700 700
2.2 2.2 2.2
0.25 0.4 0.2
– – –
– – –
130 130
640 640
0.7 0.7
– –
HEAD BODY
LEXANa LEXANa
120 120 120 140 120 120
780 780 630 630 525 525
2.7 2.7 2.7 2.7 2.6 2.7
– – – – – –
HEAD BODY – – – –
PMMA PMMA PTFEb PTFEb PTFEb PTFEb
130
750
1.0
0.3
–
PEEKd
120 120 120 120 120 120 120 100 130 100 130
487 487 608 608 606 606 606 606 606 606 606
3.5 3.5 3.5 3.5 1.4 1.4 1.4 1.4 1.4 1.4 1.4
– 0.25 – 0.25 0.1 0.1 0.1 0.1 0.1 0.1 0.1
– – – – – – – – – – –
Al Al Al Al Al Al Al Al Al Al Al
a
LEXAN is polycarbonate. PTFE is polytetrafluoroethylene. c Datasets 9, 20, 21, 22, and 23 relate to alternative applied potential settings for selected scanners. d PEEK is polyetheretherketone. e Philips Tomoscan 300 series scanners have options for the variation of focus-to-axis distance (geometric enlargement setting) and for the inclusion of additional copper filtration. b
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distance, and total filtration), selected to cover 27 models of CT scanner from five different manufacturers, which were in common use in the UK in the late 1980s (Table D.3). Shaped (bow-tie) filters have been modelled where necessary. The exposure conditions assumed for the 23 sets of calculations and the appropriate CT scanner models are listed below. Report NRPB-R250 (Jones and Shrimpton, 1991) contains tables of conversion coefficients relating doses to 27 organs or regions of the phantom to the CK,m for each of the 208 5 mm slabs and for four of the datasets listed below. Report NRPB-SR250 is a software report that contains a computer disk on which the conversion coefficients for all the datasets listed below are recorded. The 27 organs and regions of the phantom for which conversion coefficients have been calculated are the following.
interest. In these early (pre-1990) calculations kerma calculated on the axis of rotation of the scanner was expressed in terms of ICRU muscle tissue, Km, not as air kerma Ka. Consequently the CK should be converted into CT kerma index expressed in terms of absorbed dose to ICRU muscle, CK,m, when using these conversion coefficients to estimate organ doses. Conversion coefficients relating organ doses to CK,m measured free-in-air on the scanner axis for any complete CT examination of the head or trunk can be obtained by suitable summation of the conversion coefficients for the irradiation of the individual 5-mm-thick slabs.
PATIENT DOSIMETRY FOR X RAYS USED IN MEDICAL IMAGING
Adrenals Brain Breasts Eye lens Gall bladder Heart Kidneys Liver Lower large intestine
Table D.4. Organ doses DT/mGy for routine chest CT examination, region 1, using NRPB-SR250 Monte Carlo data and CTDOSE software for the examination conditions given in Section D.4.4.
Testes Thymus Thyroid Upper large intestine Urinary bladder Uterus Head region Trunk region Leg region
Application of the reports
The information required to estimate organ doses for CT examinations using the conversion coefficients tabulated in NRPB-R250 and listed in NRPB-SR250 is CK,m for the particular scanning parameters in clinical use (tube voltage, PIt, slice thickness, focus-to-axis distance, and filtration). Linearity of CK,m with PIt is assumed. The conversion coefficients need to be summed for all of the 5-mm-thick slabs that lie within the scanned volume for a particular CT examination. The value of DT to a given organ from the CT slices imaged within a scanned volume is given by zu X DT ¼ CK;m p cT,CK;m , ðD:1Þ zl
where p is the ‘packing factor’ and the conversion coefficients for the required organ are summed between the lower (zl) and upper (zu) boundaries of the scanned volume. The packing factor takes account of the relationship between slice thickness and table increment during a sequence of serial slices (or the pitch during a helical scan). For serial scans wn , ðD:2Þ p¼ L where w is the slice thickness, n the number of slices, L the total length of the scan, and p ¼ 1 for contiguous slices, p > 1 for overlapping slices, and p < 1 for gaps between slices. For helical scans, p ¼ the pitch. Organ doses can be estimated for any CT examination of the head or trunk, using a software package called CTDOSE developed at the National Radiation Laboratory, Christchurch, New Zealand. This software processes the data in NRPB-SR250 according to the requirements of the user. An example of part of the results produced by this software for a CT examination of the chest on a Philips Tomoscan LX scanner with just one series of scans
Organ
DT/mGy
Adrenals Brain Breasts Eye lens Gall bladder Stomach Small intestine ULI LLI Oesophagus Heart Kidneys Liver Lungs Ovaries Pancreas Skin Spleen Testes Muscle Thymus Thyroid Urinary bladder Uterus Head region Trunk region Leg region Bone ABM
2.97 0.08 17.50 0.07 0.76 1.55 0.10 0.14 0.02 31.90 23.10 0.61 2.37 20.60 0.02 2.30 3.24 1.75 0.0004 3.73 31.90 1.86 0.005 0.029 0.62 7.86 0.0002 9.76 5.05
(one ‘region’) and the specified scanning parameters is shown in Section D4.4. CTDOSE allows up to four series of scans (‘regions’) involving the use of different slice thickness, PIt, and table increment combinations in any one CT examination. With no esophagus modelled in the phantom, the dose to the esophagus is taken to be the same as the dose to the thymus. D.4.4
Illustrative calculation
Organ doses DT for routine chest CT examinations, region 1, according to NRPB-R250 combined with CTDOSE. The scan was performed with a tube voltage of 125 kV, PIt of 350 mA·s, CK,m/PIt of 0.220 mGy (mA·s)1, slice thickness of 10 mm, table increment of 10 mm, number of slices 20, start position of 430 mm, and end position of 650 mm. The resulting organ doses are given in Table D.4.
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D.4.3
Lungs Ovaries Pancreas Active BM Skeleton (bone surfaces) Skin Small intestine Spleen Stomach
doi:10.1093/jicru/ndi032
APPENDIX D: REPORTS PRODUCED BY THE HEALTH PROTECTION AGENCY (HPA) (FORMERLY NATIONAL RADIOLOGICAL PROTECTION BOARD, NRPB) GENERAL DESCRIPTION
NRPB has produced three sets of reports that permit estimation of the mean absorbed doses to 25 different tissues and organs in reference adult and paediatric patients from common radiographic, fluoroscopic, and CT examinations. The three sets of reports deal with the following. 1. Common Adult X-ray Examinations 2. Common Paediatric X-ray Examinations 3. Adult Computedtomography Examinations
(NRPB-R262, NRPB-SR262, Hart et al., 1994a,b) (NRPB-R279, NRPB-SR279, Hart et al., 1996a,b) (NRPB-R250, NRPB- SR250 Jones and Shrimpton, 1991, 1993)
Each set consists of a pair of NRPB reports, one providing printed tabulations of conversion coefficients for a sample of the available data and the other (the ‘software report’, denoted ‘NRPB-SR . . .’) includes a computer disk containing a complete listing of all the available dose-conversion coefficients. The listing is arranged in a large series of data files, which can be incorporated into suitable computer programs for processing the conversion coefficients in a manner matched to the requirements of the user. Such user-friendly software packages, which calculate organ doses for any combination of x-ray examination parameters specified by the user, are available from the National Radiation Laboratory, Christchurch, New Zealand, for each set of NRPB reports. The dose-conversion coefficients in the software reports relate organ dose DT/mGy to entrance surface air kerma, Ka,e/mGy and to air kerma–area product, PKA/(Gy cm2) for radiographic and fluoroscopic examinations and to CT kerma index
expressed in ICRU muscle tissue, CK,m/mGy for CT examinations. The same basic Monte Carlo code developed at NRPB is used for all three sets of calculations and both adult and paediatric patients are simulated by hermaphrodite mathematical phantoms. The software reports include organ dose-conversion coefficients for a large number of diagnostic radiation qualities or types of CT scanner.
D.2 REPORT NRPB-SR262 (HART ET AL., 1994b): COMMON ADULT X-RAY EXAMINATIONS D.2.1
Main features of calculations
Details of the Monte Carlo code and the mathematical phantom developed at NRPB are described by Jones and Wall (1985). Conversion coefficients relating DT to Ka,e and to PKA were calculated by simulating typical x-ray examination exposure conditions on a hermaphrodite mathematical phantom representing a typical adult patient. Four million photon histories were followed for each x-ray examination field simulated. The phantom was based on Cristy’s adult hermaphrodite phantom (Cristy, 1980) with Kramer’s modified neck region (Kramer et al., 1982), a breast tissue composition of 50 % fat and 50 % water, and with an esophagus. The arms of the phantom, which lie alongside the trunk, were removed when lateral projections through the trunk were simulated.
D.2.2
Scope of the report
Report NRPB-SR262 (Hart et al., 1994b) is a software report, which includes a computer disk containing files of conversion coefficients relating DT to Ka,e and to PKA for the 68 radiographic projection (e.g., Head) and view (e.g., AP) combinations listed below.
Ó International Commission on Radiation Units and Measurements 2005
Downloaded from http://jicru.oxfordjournals.org/ at University of Prince Edward Island on February 21, 2015
D.1
PATIENT DOSIMETRY FOR X RAYS USED IN MEDICAL IMAGING
Heart LAT L and R Heart LAO, RAO Upper stomach AP, PA Stomach RAO, LPO, LAO Stomach AP, PA, Stomach LAT (L) Kidneys AP, PA Lumbar spine LPO, RPO Lumbar spine AP Lumbar spine LAT L and R Left flexure LAO Right flexure RAO
using the conversion coefficients listed in NRPBSR262 is Ka,e or PKA for each radiograph and the corresponding tube voltage and total beam filtration. Organ doses can be estimated for any combination of the 68 radiographic projections and views, using a software package called XDOSE developed at the National Radiation Laboratory, Christchurch, New Zealand. This software processes the data in NRPBSR262 according to the requirements of the user. An example of part of the results produced by this software for a PA chest radiograph and an AP abdominal radiograph with specified exposure factors is shown in Table D.1.
The focus-to-surface distance dFSD, the position of the central axis of the x-ray beam in the phantom, and the x-ray field size at the image receptor and at the mid-plane of the phantom, for all the above radiographic projections are described in the report. The mid-plane field size is also shown diagrammatically on a drawing of the phantom so that the position of the x-ray field in relation to all the modelled organs can be visualized. For each radiographic projection and view, conversion coefficients are tabulated for 40 x-ray spectra, specified by the peak tube voltage and the total beam filtration. Tube voltages range from 50 to 120 kV, in 10 kV steps; and five total beam filtrations of 2, 2.5, 3, 4, and 5 mm Al are included for each tube voltage. The source of the x-ray spectra data for these calculations is an updated (1991) version of the computer program of Iles (1987). This program produces results very similar to that published by the IPEM (1997). In NRPB-SR262 (Hart et al., 1994b) conversion coefficients are given for 26 organs for the 68 radiographic projection and view combinations and 40 x-ray spectra described above. These 26 organs are the following. Adrenals Brain Breasts Eye Lens Gall bladder Heart Kidneys Liver Lower large intestine
D.2.3
Lungs Oesophagus Ovaries Pancreas Active BM Residual tissues (muscle) Skeleton (bone surfaces) Skin Small intestine
Duodenum AP, PA Duodenum RAO, LPO LSJ LAT L and R Abdomen AP, PA Small intestine AP, PA Pelvis/colon AP, PA Colon RAO, LPO, LAO Urinary bladder AP Hip AP L and R Rectum AP, PA Rectum LAT L and R Rectum LPO, RAO
D.2.4
Illustrative calculation
Organ doses DT for chest PA and abdomen AP examinations were calculated using NRPB-SR262 Monte Carlo data (Hart et al., 1994b). The chest PA examination is performed with a tube voltage of 120 kV, a filtration of 3.00 mm Al, and at the reference dFSD. The entrance air kerma Ka,e for the chest examination is 0.16 mGy. The abdomen AP examination is performed with a tube voltage of 85 kV, a filtration of 3.00 mm Al, and at the reference dFSD. The entrance air kerma Ka,e for the abdomen examination is 5.60 mGy. The results of the organ dose calculation are given in Table D.1.
Spleen Stomach Testes Thymus Thyroid Upper large intestine Urinary bladder Uterus
D.3 REPORT NRPB-SR279 (HART ET AL., 1996b): COMMON PAEDIATRIC X-RAY EXAMINATIONS D.3.1
Main features of calculations
Details of the Monte Carlo code developed at NRPB are described by Jones and Wall (1985). Conversion coefficients relating DT to Ka,e and to PKA were calculated by simulating typical x-ray examination exposure conditions on a series of five hermaphrodite mathematical phantoms representing newborn, 1, 5, 10, and 15-year-old patients. Four million photon histories were followed for each xray examination field that was simulated. The
Application of the report
The information required to estimate organ doses from 68 adult radiographic projections and views 88
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Head AP, PA Head LAT L and R Cervical spine AP Cervical spine LAT L and R Throat LAT L and R Shoulder AP L and R Oesophagus RAO, LAO, LPO Thoracic spine AP Thoracic spine LAT L and R Chest AP, PA Chest LAT L and R Heart AP, PA
APPENDIX D Table D.1. Organ doses DT/mGy calculated for chest PA and abdomen AP examinations using NRPB-SR262 Monte Carlo data and the software package XDOSE for the examination conditions given in Section D.2.4. Organ
D.3.2
Report NRPB-SR279 (Hart et al., 1996b) contains files of conversion coefficients relating DT to Ka,e and to PKA for the 18 radiographic projections and views listed below.
DT/mGy Abdomen AP
0.0970 0.0006 0.0197 0.0003 0.0187 0.0238 0.0025 0.0032 0.0006 0.0362 0.0608 0.0419 0.0846 0.0005 0.0453 0.0163 0.0803 0.00 0.0184 0.0108 0.0001 0.0005 0.0490 0.0181 0.0485 0.0274
0.261 0.00 0.0199 0.00 1.95 1.95 1.64 1.98 1.32 0.0675 0.366 1.08 0.0474 1.28 0.872 0.387 0.507 0.243 0.0094 0.0003 2.61 1.67 0.0643 0.531 0.289 0.217
Head AP, PA, LAT Cervical spine AP, PA, LAT Chest AP, PA, LAT
0 1 5 10 15
Weight/ kg
3.47 9.26 19.0 31.9 54.4
Height/ cm
51.5 75.0 109.0 138.6 164.0
Thickness of head/cm
Thickness of trunk/ cm
AP
LAT
AP
LAT
11.6 15.7 18.1 18.8 19.5
9.0 12.3 14.3 14.9 15.5
9.8 13.0 15.0 16.8 19.6
12.7 17.6 22.9 27.8 34.5
Urinary bladder AP, PA
The dFSD, the position of the central axis of the x-ray beam in each phantom, and the x-ray field size at the image receptor, for all the above radiographic projections are described in the report. The field size at the mid-plane of the phantom is also shown diagrammatically on a drawing of each phantom so that the position of the x-ray field in relation to all the modelled organs can be visualized. For each radiographic projection and view, conversion coefficients are tabulated for 72 x-ray spectra, specified by the peak tube voltage and the total beam filtration. Tube voltage ranges from 50 to 120 kV, in 10 kV steps. For each tube voltage nine total beam filtrations are included, the same five as for the previous adult examinations (i.e., 2, 2.5, 3, 4, and 5 mm Al) and a further four involving additional copper filtration that has been recommended for paediatric radiography (EC 1996d), i.e., 2 mm Al þ 0.1 mm Cu; 2 mm Al þ 0.2 mm Cu; 3 mm Al þ 0.1 mm Cu and 3 mm Al þ 0.2 mm Cu. The source of the x-ray spectra data for these calculations is an updated (1991) version of the computer program of Iles (1987). This program produces very similar results to that published by the IPEM (1997). In NRPB-SR279 (Hart et al., 1996b) conversion coefficients for 26 organs are given for the 18 radiographic projections and views and the 72 x-ray spectra described above. These organs are the following.
phantoms were based on Cristy’s hermaphrodite phantoms (Cristy, 1980) and Kramer’s modified neck region (Kramer et al., 1982) was applied to all of them. An esophagus was added to each phantom. A suitable volume of breast tissue was included in each phantom and in the absence of specific information on the fat content of breast tissue in young children, 50 % fat and 50 % water was used as the breast tissue composition for all of the phantoms. The arms of the phantom, which lie alongside the trunk, were removed when lateral projections through the trunk were simulated. The weights and major dimensions of the five paediatric phantoms are shown below. Age/ years
Lumbar spine AP, PA, LAT Abdomen AP, PA Pelvis AP, PA
Adrenals Brain Breasts Eye lens Gall bladder Heart Kidneys Liver Lower large intestine
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Lungs Oesophagus Ovaries Pancreas Active BM Residual tissues (muscle) Skeleton (bone surfaces) Skin Small intestine
Spleen Stomach Testes Thymus Thyroid Upper large intestine Urinary bladder Uterus
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Adrenals Brain Breasts Eye lens Gall bladder Stomach Small intestine Upper large intestine Lower large intestine Heart Kidneys Liver Lungs Ovaries Pancreas Skin Spleen Testes Thymus Thyroid Urinary bladder Uterus Oesophagus Muscle Total bone Active BM
Chest PA
Scope of the report
PATIENT DOSIMETRY FOR X RAYS USED IN MEDICAL IMAGING
D.3.3
D.3.4
Application of the report
D.4 REPORTS NRPB-R250, NRPB-SR250 (JONES AND SHRIMPTON, 1991, 1993): ADULT CT EXAMINATIONS D.4.1
The same Monte Carlo code and adult hermaphrodite mathematical phantom were used as in the calculations for conventional x-ray examinations (see Appendix D.2.1). Only the esophagus was missing from the phantom described in Appendix D.2.1. The arms of the phantom remained alongside the trunk for all simulated CT examinations, as is the usual practice with patients. To simulate the distinct exposure conditions prevailing during CT examinations, the x-ray source was rotated around the long axis of the phantom. Organ doses were determined for the individual irradiation of 208 contiguous 5-mm-thick transverse slabs of the phantom ranging from the top of the head to the top of the legs. A line x-ray source of the same length of each irradiated slab (5 mm) was used, with the photons emitted normally from the source into a fan-shaped beam spanning the width of the phantom. An abrupt cut-off of the x-ray beam at the edges and faces of the fan (i.e., perfect collimation) is a feature of this model. Conversion coefficients were calculated relating the organ doses to the kerma on the axis of rotation of the scanner free-in-air, i.e., with no phantom or patient present. The imperfect collimation of the x-ray beam in the axial direction, which occurs in practice, can lead to a build-up of dose in adjacent scans. However, this is taken account of by measuring the CT kerma index free-in-air, CK, under the exposure conditions, i.e., slice thickness, tube voltage, and tube-current exposure-time product, PIt. The value of CK is then multiplied by the conversion coefficients to estimate the organ doses for the degree of beam collimation achieved by the CT scanner of
Table D.2. Organ doses DT/mGy for child of 1 year calculated for chest PA and abdomen AP examinations using NRPB-SR279 Monte Carlo data and CHILDOSE software for the examination conditions given in Section D.3.4.
Adrenals Brain Breasts Eye lens Gall bladder Stomach Small intestine Upper large intestine Lower large intestine Heart Kidneys Liver Lungs Ovaries Pancreas Skin Spleen Testes Thymus Thyroid Urinary bladder Uterus Oesophagus Muscle Total bone Active BM
DT/mGy for child of 1 year Chest PA
Abdomen AP
0.0215 0.0002 0.0105 0.0002 0.0026 0.0049 0.0008 0.0009 0.0002 0.0144 0.0029 0.0081 0.0311 0.0004 0.0079 0.0063 0.0107 0.00 0.0080 0.0060 0.0001 0.0003 0.0177 0.0068 0.0259 0.0060
0.0796 0.0001 0.0102 0.0002 0.252 0.271 0.211 0.242 0.152 0.0440 0.0796 0.226 0.0390 0.184 0.167 0.0468 0.118 0.0335 0.0065 0.0024 0.264 0.216 0.0508 0.0748 0.0860 0.0274
Main features of calculations
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Organ doses DT for chest PA and abdomen AP examinations were calculated using NRPB-SR279 Monte Carlo data (Hart et al., 1996b) for child of 1 year. The chest PA examination is performed with a tube voltage of 90 kV, a filtration of 2.00 mm Al and of 0.10 mm Cu, and at the reference dFSD. The entrance air kerma Ka,e for the chest examination is 0.05 mGy. The abdomen AP examination is performed with a tube voltage of 90 kV, a filtration of 2.00 mm Al and 0.10 mm Cu, and at the reference dFSD. The entrance air kerma Ka,e for the abdomen examination is 0.40 mGy. The results of the organ dose calculation are given in Table D.2.
The information required to estimate organ doses from 18 paediatric radiographic examinations using the conversion coefficients listed in NRPBSR279 is the Ka,e or the PKA for each radiograph and the corresponding tube voltage and total beam filtration. Organ doses to any of the phantoms representing a newborn, 1, 5, 10, or 15-year-old patient can be estimated for any combination of the 18 radiographic projections, using a software package called CHILDOSE developed at the National Radiation Laboratory, Christchurch, New Zealand. This software processes the data in NRPB-SR279 according to the requirements of the user. An example of part of the results produced by this software for an examination comprising a PA chest radiograph and an AP abdominal radiograph on a 1-year-old child with the specified exposure factors is shown in Table D.2.
Organ
Illustrative calculation
APPENDIX D
D.4.2
Scope of the reports
Calculations have been performed for 23 sets of exposure conditions (i.e., tube voltage, focus-to-axis
Table D.3. Exposure conditions for calculation of normalized organ doses for CT using Monte Carlo techniques according to Jones and Shrimpton (1991, 1993). Monte Carlo data set no.
1 2 3 4 5 6 7 8 9c 10 11 12 13 14 15 16 17 18 19 20c 21c 22c 23c
CT scanner models for which data set is appropriate
Siemens Somatom 2,DR1/2/3 Somatom DRG,DRG1 Somatom DRH,CR,CR512 Picker 1200SX 1200SX GE CT 8800,9000I/II/HP CT 8800,9000I/II/HP CT 9800,9800Quick CT 9800,9800Quick CT MAX CT PACE CGR CE 10000,12000 Philipse Tomoscan 305N,310,350 (GE No. 2, no Cu) Tomoscan 305N,310,350 (GE No. 2, with Cu) Tomoscan 310,350 (GE No.3, no Cu) Tomoscan 310,350 (GE No. 3, with Cu) Tomoscan TX Tomoscan CX,CX/S Tomoscan LX Tomoscan TX Tomoscan TX Tomoscan LX Tomoscan LX
Tube voltage/kV
Focus to axis distance/mm
Flat filter/
Shaped filter/
Al mm
Cu mm
Option
Type
125 125 125
760 700 700
2.2 2.2 2.2
0.25 0.4 0.2
– – –
– – –
130 130
640 640
0.7 0.7
– –
HEAD BODY
LEXANa LEXANa
120 120 120 140 120 120
780 780 630 630 525 525
2.7 2.7 2.7 2.7 2.6 2.7
– – – – – –
HEAD BODY – – – –
PMMA PMMA PTFEb PTFEb PTFEb PTFEb
130
750
1.0
0.3
–
PEEKd
120 120 120 120 120 120 120 100 130 100 130
487 487 608 608 606 606 606 606 606 606 606
3.5 3.5 3.5 3.5 1.4 1.4 1.4 1.4 1.4 1.4 1.4
– 0.25 – 0.25 0.1 0.1 0.1 0.1 0.1 0.1 0.1
– – – – – – – – – – –
Al Al Al Al Al Al Al Al Al Al Al
a
LEXAN is polycarbonate. PTFE is polytetrafluoroethylene. c Datasets 9, 20, 21, 22, and 23 relate to alternative applied potential settings for selected scanners. d PEEK is polyetheretherketone. e Philips Tomoscan 300 series scanners have options for the variation of focus-to-axis distance (geometric enlargement setting) and for the inclusion of additional copper filtration. b
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distance, and total filtration), selected to cover 27 models of CT scanner from five different manufacturers, which were in common use in the UK in the late 1980s (Table D.3). Shaped (bow-tie) filters have been modelled where necessary. The exposure conditions assumed for the 23 sets of calculations and the appropriate CT scanner models are listed below. Report NRPB-R250 (Jones and Shrimpton, 1991) contains tables of conversion coefficients relating doses to 27 organs or regions of the phantom to the CK,m for each of the 208 5 mm slabs and for four of the datasets listed below. Report NRPB-SR250 is a software report that contains a computer disk on which the conversion coefficients for all the datasets listed below are recorded. The 27 organs and regions of the phantom for which conversion coefficients have been calculated are the following.
interest. In these early (pre-1990) calculations kerma calculated on the axis of rotation of the scanner was expressed in terms of ICRU muscle tissue, Km, not as air kerma Ka. Consequently the CK should be converted into CT kerma index expressed in terms of absorbed dose to ICRU muscle, CK,m, when using these conversion coefficients to estimate organ doses. Conversion coefficients relating organ doses to CK,m measured free-in-air on the scanner axis for any complete CT examination of the head or trunk can be obtained by suitable summation of the conversion coefficients for the irradiation of the individual 5-mm-thick slabs.
PATIENT DOSIMETRY FOR X RAYS USED IN MEDICAL IMAGING
Adrenals Brain Breasts Eye lens Gall bladder Heart Kidneys Liver Lower large intestine
Table D.4. Organ doses DT/mGy for routine chest CT examination, region 1, using NRPB-SR250 Monte Carlo data and CTDOSE software for the examination conditions given in Section D.4.4.
Testes Thymus Thyroid Upper large intestine Urinary bladder Uterus Head region Trunk region Leg region
Application of the reports
The information required to estimate organ doses for CT examinations using the conversion coefficients tabulated in NRPB-R250 and listed in NRPB-SR250 is CK,m for the particular scanning parameters in clinical use (tube voltage, PIt, slice thickness, focus-to-axis distance, and filtration). Linearity of CK,m with PIt is assumed. The conversion coefficients need to be summed for all of the 5-mm-thick slabs that lie within the scanned volume for a particular CT examination. The value of DT to a given organ from the CT slices imaged within a scanned volume is given by zu X DT ¼ CK;m p cT,CK;m , ðD:1Þ zl
where p is the ‘packing factor’ and the conversion coefficients for the required organ are summed between the lower (zl) and upper (zu) boundaries of the scanned volume. The packing factor takes account of the relationship between slice thickness and table increment during a sequence of serial slices (or the pitch during a helical scan). For serial scans wn , ðD:2Þ p¼ L where w is the slice thickness, n the number of slices, L the total length of the scan, and p ¼ 1 for contiguous slices, p > 1 for overlapping slices, and p < 1 for gaps between slices. For helical scans, p ¼ the pitch. Organ doses can be estimated for any CT examination of the head or trunk, using a software package called CTDOSE developed at the National Radiation Laboratory, Christchurch, New Zealand. This software processes the data in NRPB-SR250 according to the requirements of the user. An example of part of the results produced by this software for a CT examination of the chest on a Philips Tomoscan LX scanner with just one series of scans
Organ
DT/mGy
Adrenals Brain Breasts Eye lens Gall bladder Stomach Small intestine ULI LLI Oesophagus Heart Kidneys Liver Lungs Ovaries Pancreas Skin Spleen Testes Muscle Thymus Thyroid Urinary bladder Uterus Head region Trunk region Leg region Bone ABM
2.97 0.08 17.50 0.07 0.76 1.55 0.10 0.14 0.02 31.90 23.10 0.61 2.37 20.60 0.02 2.30 3.24 1.75 0.0004 3.73 31.90 1.86 0.005 0.029 0.62 7.86 0.0002 9.76 5.05
(one ‘region’) and the specified scanning parameters is shown in Section D4.4. CTDOSE allows up to four series of scans (‘regions’) involving the use of different slice thickness, PIt, and table increment combinations in any one CT examination. With no esophagus modelled in the phantom, the dose to the esophagus is taken to be the same as the dose to the thymus. D.4.4
Illustrative calculation
Organ doses DT for routine chest CT examinations, region 1, according to NRPB-R250 combined with CTDOSE. The scan was performed with a tube voltage of 125 kV, PIt of 350 mA·s, CK,m/PIt of 0.220 mGy (mA·s)1, slice thickness of 10 mm, table increment of 10 mm, number of slices 20, start position of 430 mm, and end position of 650 mm. The resulting organ doses are given in Table D.4.
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D.4.3
Lungs Ovaries Pancreas Active BM Skeleton (bone surfaces) Skin Small intestine Spleen Stomach
