Radiation Protection Dosimetry (2015), Vol. 165, No. 1–4, pp. 430 –433 Advance Access publication 5 April 2015
doi:10.1093/rpd/ncv128
PATIENT DOSES FROM PET-CT PROCEDURES S. Avramova-Cholakova1,*, S. Ivanova2, E. Petrova3, M. Garcheva3 and J. Vassileva1 1 National Centre of Radiobiology and Radiation Protection, Sofia, Bulgaria 2 University Multiprofile Hospital for Active Treatment ‘St Marina’, Varna, Bulgaria 3 University Multiprofile Hospital for Active Treatment ‘Alexandrovska’, Sofia, Bulgaria *Corresponding author: [email protected] Positron emission tomography (PET) was installed for the first time in Bulgaria in 2009, and nowadays two hybrid PET-computed tomography (CT) systems are in operation. The aim of this work is to estimate patient doses from PET-CT procedures and to explore potential for optimisation. Data were retrospectively collected for 50 patients examined with the system Philips Gemini TF and for 58 patients examined with the system GE Discovery 600. Whole-body examinations with radiopharmaceutical 18F-2-fluoro-2-deoxy-D-glucose (FDG) were performed on all patients. Patient effective doses from the CT component of the examination were calculated with CT Expo software and compared with doses estimated applying the National Radiological Protection Board (NRPB) conversion coefficients. Effective doses from the PET component were calculated applying the ICRP 80 conversion coefficients. For the first system, average effective doses from CT component were 8.0 and 8.9 mSv, applying CT Expo and NRPB coefficients, respectively, and 4.9 mSv from PET component. For the second system, the corresponding values were 7.8, 8.7 and 5.9 mSv. These results for patient effective doses are relatively lower or comparable to other similar surveys. Reasons for the observed differences are analysed and presented.
INTRODUCTION After the first commercially available hybrid positron emission tomography and computed tomography (PET-CT) system appeared on the market in 2001, this technology proved to be of high value for the medical practice(1). However, because of the combination of two radiation modalities, patient doses are relatively high. The first two PET-CT systems were installed in Bulgaria in 2009–2011, and a third one is under commissioning. The aim of this work is to estimate for the first time in Bulgaria patient doses from PET-CT systems and to explore potential for optimisation by comparison with published data.
software (version 2.1, Medizinische Hochschule, Hannover, Germany). It has the possibility to calculate E depending on patient sex and applying the ICRP 60(2) or ICRP 103(3) tissue weighting factors. Average CTDI and DLP values for both sexes were used to estimate effective dose separately, for each scanner, each sex and each body part scanned. Then, average effective dose for both sexes was calculated. The second method for calculation of E from CT modality used the National Radiological Protection Board (NRPB) conversion coefficients, multiplied by the DLP(4). The PET contribution to E was calculated multiplying the average activities by the ICRP 80 conversion coefficients(5). RESULTS AND DISCUSSION
MATERIALS AND METHODS Two PET-CT scanners operating clinically were studied: Gemini TF (Philips Healthcare), denoted as System I, and Discovery 600 (GE Healthcare), denoted as System II, both with 16-detector row CT. Standard forms for data collection were sent to the departments, with data to be recorded including patient sex, age, weight and height, as well as CT exposure parameters: tube voltage (kV), tube current (mA), rotation time, pitch, slice collimation, computed tomography dose index (CTDI), dose length product (DLP) and activity of radiopharmaceutical (RF) applied. Patient data were retrospectively collected from the archives of the facilities. Effective dose E from the CT component was calculated using two methods. The first method used the CT Expo
The number of patients per system and the type of examination, the mean values, minimum and maximum values in brackets, and standard deviation after brackets, for administered activity, CTDI and DLP are presented in Table 1. All examinations were performed with 18F-2-fluoro-2-deoxy-D-glucose (FDG). Two types of examinations were performed. The most common type, named here ‘standard examination’, included head and body till mid thighs. The second examination, named ‘whole-body examination’, involved scanning of the whole body, including head, till feet. The whole-body examination was performed for a small number of patients with diagnosis melanoma malignum. The main technical parameters used in the CT protocols are presented in Table 2. Automatic exposure control (AEC) denotes that tube current modulation
# The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
PATIENT DOSES FROM PET-CT Table 1. The number of patients, administered activity, CTDI and DLP per type of examination and system. Examination
Standard Whole body
PET-CT system
No. of patients
Amean (min., max.); SD (MBq)
CTDImean (min., max.); SD (mGy)
DLPmean (min., max.); SD (mGy cm)
I II I II
43 52 7 6
258 (185, 418); 56 313 (153, 511); 73 258 (185, 418); 55.8 313 (153, 511); 73
5.9 (4.2, 8.5); 1 5.4 (1.8, 11.1); 2 6.2 (4.2, 8.5); 1.4 3.7 (2.3, 4.6); 1
591 (395, 1012); 130 575 (194, 1242); 248 1112 (712, 1581); 285 620 (428, 811); 166
Mean values are presented, minimum and maximum values in parentheses and standard deviation (SD). Table 2. Main technical parameters used for CT scanning. Examination
Standard Whole body
PET-CT system
kV
Rotation time (s)
Slice thickness (no. of rows`mm)
Pitch
AEC/mean mA s
I II I II
120 120 120 120
0.5 not provided 0.5 not provided
16` 1.5 3.75 16` 1.5 3.75
0.69 not provided 0.69 not provided
AEC/84 AEC/not provided AEC/89 AEC/not provided
AEC, automatic exposure control.
is used. The same protocol for both types of examinations was used to perform CT with System I. For System II, the whole-body examination was performed with lower-dose protocol, which can be seen from the lower CTDI values (Table 1, mean CTDI 5.4 mGy for the standard and 3.7 mGy for the wholebody exam on II). The activities of RF administered to patients depended on the patient body mass and not on the type of examination. The calculated effective doses are presented in Figures 1 and 2 for standard and whole-body examinations, respectively, in the following order: first column is E from CT derived applying the NRPB method (only in Figure 1), the second column is E with CT Expo and ICRP 60 tissue weighting factors, the third column is E with CT Expo and ICRP 103 tissue weighting factors, the fourth is the PET contribution to E and the fifth is total effective dose from the PET-CT examination, taking into account the CT contribution calculated with CT Expo and ICRP 103. The conversion coefficient for the trunk region was used with the NRPB method for the standard examination(4). This is probably the reason for the higher value of E obtained with this method, compared with CT Expo, because the real scanned anatomic region included much longer part of the body than only trunk. This led to higher DLP values and hence E. CT contribution of 8.9 mSv was found for System I with the NRPB method, compared with 8.0 and 7.8 mSv with CT Expo and ICRP 60, and CT Expo and ICRP 103, respectively (Figure 1). CT contribution of 8.7 mSv was calculated with the NRPB method for System II, and 7.8 and 7.7 mSv with CT Expo and
Figure 1. Effective doses for the standard PET-CT examination for Systems I and II. The first column shows E in millisievert from CT component, calculated with NRPB conversion coefficients; the second column shows E calculated with CT Expo applying ICRP 60 tissue weighting factors; the third column shows E with CT Expo applying ICRP 103 factors; the fourth column shows E from the PET component and the fifth shows E from the whole examination, taking into account CT contribution with CT Expo and ICRP 103.
ICRP 60, and CT Expo and ICRP 103, respectively. It should be taken into account that the NRPB coefficients are published for ICRP 60 tissue weighting factors(4). The effective doses from CT for the standard exam are comparable for both systems, with differences entirely within the uncertainty of the methods. However, higher activities of radiopharmaceuticals (Table 1) were observed for System II, resulting in higher PET contribution to E (4.9 mSv for System I vs. 5.9 mSv for System II). The reason is that System I has the time-of-flight option, not present
431
S. AVRAMOVA-CHOLAKOVA ET AL.
Figure 2. Effective doses the whole-body PET-CT examination for Systems I and II. The first column shows E in millisievert from CT component, calculated with CT Expo applying ICRP 60 tissue weighting factors; the second column shows E with CT Expo applying ICRP 103 factors; the third column shows E from the PET component and the fourth shows E from the whole examination, taking into account CT contribution with CT Expo and ICRP 103.
at System II. It allows lower activities to be used without compromising image quality(6). The total E for System II was consecutively higher (13.6 mSv), while for System I it was 12.7 mSv for the standard examination. Because of the lower-dose CT protocol used on System II, the CT contribution to the whole-body examination was 5.9 mSv (CT Expo, ICRP 103) versus 9.4 mSv for System I (Figure 2). Consecutively, the total E for System I is higher—14.5 mSv, versus 11.8 mSv for System II, regardless of the higher mean administered activity. Brix et al. reported effective doses from PET-CT examinations in four hospitals in Germany of the order of 24–26 mSv(7). These examinations included a diagnostic CT scan in most cases, and in only some of the hospitals, a low-dose CT was performed. The diagnostic CT was estimated to deliver 14.1– 18.6 mSv, while the low-dose CT was reported to contribute to 1.3 –4.5 mSv. The values for Systems I and II are higher than the latter reported by Brix but much lower than the diagnostic CT values. It should be taken into account in this comparison that the body region scanned reported by Brix had lower limit defined by the symphysis (the gonads receiving only scattered radiation), while all examinations on our systems were in fact whole body. The PET contribution according to Brix is 5.7–7 mSv with 18F-FDG (300 or 370 MBq), which is comparable with or higher than Systems I and II in this study. Huang et al. performed similar study with one PET-CT scanner(8). For the most frequently used CT protocol, they measured about 7 mSv for standard patient, represented by Alderson-Rando phantom.
This value is lower than that calculated in our study, but the phantom used represented 163 cm high and 54 kg weighing human, used for both female and male by removing breast attachments. In this study for System I, the mean height of patients was 167 cm and the mean weight was 73 kg, and correspondingly 169 cm and 74 kg for System II, which can explain the higher values of E. For obese patients, Huang reported effective dose from CT up to about 19 mSv with the same protocol. The PET contribution was 6.2 mSv (using 370 MBq 18F-FDG), similar to or higher than our values. Khamwan et al. reported 14.5 mSv from CT and 4.4 mSv from PET for the same type of examinations, with a total of 18.9 mSv(9). The CT contribution and the total E reported by these authors are higher than those calculated here. Kaushik et al. estimated total effective dose from a typical protocol of whole-body PET-CT examination, 14.4 mSv for females and 11.8 mSv for male patients, from 18F-FDG that is in a good agreement with our results(10). Tonkopi et al. elaborated optimised CT protocol for whole-body PET-CT with a reduction of CT effective dose from 8.1 to 5.5 mSv(11). Similar values are achieved during the whole-body examination with System II. Potential for further dose reduction, especially from CT component, could be investigated on both systems. CONCLUSIONS Estimation of patient doses from PET-CT procedures was performed for the first time in the country. Effective dose for both PET-CT scanners was relatively low or comparable with similar studies, but potential for dose reduction will be further investigated, especially from the CT component. The contribution of CT to the effective dose, calculated with the NRPB conversion coefficients, had higher values, compared with the values calculated with CT Expo. This is probably due to the limitation of the conversion coefficients to the trunk region, while the longer scanning range is taken into account in the software calculation. REFERENCES
432
1. Townsend, D. Combined PET/CT: the historical perspective. Semin. Ultrasound CT MR 29(4), 232–235 (2008). 2. International Commission on Radiological Protection. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60. Ann. ICRP 21, 4– 11 (1991). 3. International Commission on Radiological Protection. The Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37, 61–71 (2007).
PATIENT DOSES FROM PET-CT 4. Shrimpton, P. C. Assessment of patient dose in CT. NRPB-PE/1/2004 (2004). 5. International Commission on Radiological Protection. Radiation dose to patients from radiopharmaceuticals. ICRP publication 80. Ann. ICRP 28, 47– 83 (1998). 6. Fakhri, G., Surti, S., Trott, C., Scheuermann, J. and Karp, J. Improvement in lesion detection with whole-body oncologic time-of-flight PET. J. Nucl. Med. 52, 347– 353 (2011). 7. Brix, G., Lechel, U., Glatting, G., Ziegler, S., Munzing, W., Muller, S. and Beyer, T. Radiation exposure of patients undergoing whole-body dual-modality 18F-FDG PET/CT examinations. J. Nucl. Med. 46(4), 608– 613 (2005).
8. Huang, B., Law, M. and Khong, P. Whole-body PET/ CT scanning: estimation of radiation dose and cancer risk. Radiology. 251(1), 166–174 (2009). 9. Khamwan, K., Krisanachinda, A. and Pasawang, P. The determination of patient dose from 18F-FDG PET/CT examination. Radiat. Prot. Dosim. 141(1), 50–55 (2010). 10. Kaushik, A., Jaimini, A., Tripathi, M., D’Souza, M., Sharma, R., Mishra, A. K., Mondal, A. and Dwarakanath, B. S. Estimation of patient dose in 18F-FDG and 18F-FDOPA PET/CT examinations. J. Can. Res. Ther. 9(3), 477–483 (2013). 11. Tonkopi, E., Ross, A. and MacDonald, A. CT dose optimization for whole-body PET/CT examinations. Am. J. Roentgenol. 201, 257– 263 (2013).
433
doi:10.1093/rpd/ncv128
PATIENT DOSES FROM PET-CT PROCEDURES S. Avramova-Cholakova1,*, S. Ivanova2, E. Petrova3, M. Garcheva3 and J. Vassileva1 1 National Centre of Radiobiology and Radiation Protection, Sofia, Bulgaria 2 University Multiprofile Hospital for Active Treatment ‘St Marina’, Varna, Bulgaria 3 University Multiprofile Hospital for Active Treatment ‘Alexandrovska’, Sofia, Bulgaria *Corresponding author: [email protected] Positron emission tomography (PET) was installed for the first time in Bulgaria in 2009, and nowadays two hybrid PET-computed tomography (CT) systems are in operation. The aim of this work is to estimate patient doses from PET-CT procedures and to explore potential for optimisation. Data were retrospectively collected for 50 patients examined with the system Philips Gemini TF and for 58 patients examined with the system GE Discovery 600. Whole-body examinations with radiopharmaceutical 18F-2-fluoro-2-deoxy-D-glucose (FDG) were performed on all patients. Patient effective doses from the CT component of the examination were calculated with CT Expo software and compared with doses estimated applying the National Radiological Protection Board (NRPB) conversion coefficients. Effective doses from the PET component were calculated applying the ICRP 80 conversion coefficients. For the first system, average effective doses from CT component were 8.0 and 8.9 mSv, applying CT Expo and NRPB coefficients, respectively, and 4.9 mSv from PET component. For the second system, the corresponding values were 7.8, 8.7 and 5.9 mSv. These results for patient effective doses are relatively lower or comparable to other similar surveys. Reasons for the observed differences are analysed and presented.
INTRODUCTION After the first commercially available hybrid positron emission tomography and computed tomography (PET-CT) system appeared on the market in 2001, this technology proved to be of high value for the medical practice(1). However, because of the combination of two radiation modalities, patient doses are relatively high. The first two PET-CT systems were installed in Bulgaria in 2009–2011, and a third one is under commissioning. The aim of this work is to estimate for the first time in Bulgaria patient doses from PET-CT systems and to explore potential for optimisation by comparison with published data.
software (version 2.1, Medizinische Hochschule, Hannover, Germany). It has the possibility to calculate E depending on patient sex and applying the ICRP 60(2) or ICRP 103(3) tissue weighting factors. Average CTDI and DLP values for both sexes were used to estimate effective dose separately, for each scanner, each sex and each body part scanned. Then, average effective dose for both sexes was calculated. The second method for calculation of E from CT modality used the National Radiological Protection Board (NRPB) conversion coefficients, multiplied by the DLP(4). The PET contribution to E was calculated multiplying the average activities by the ICRP 80 conversion coefficients(5). RESULTS AND DISCUSSION
MATERIALS AND METHODS Two PET-CT scanners operating clinically were studied: Gemini TF (Philips Healthcare), denoted as System I, and Discovery 600 (GE Healthcare), denoted as System II, both with 16-detector row CT. Standard forms for data collection were sent to the departments, with data to be recorded including patient sex, age, weight and height, as well as CT exposure parameters: tube voltage (kV), tube current (mA), rotation time, pitch, slice collimation, computed tomography dose index (CTDI), dose length product (DLP) and activity of radiopharmaceutical (RF) applied. Patient data were retrospectively collected from the archives of the facilities. Effective dose E from the CT component was calculated using two methods. The first method used the CT Expo
The number of patients per system and the type of examination, the mean values, minimum and maximum values in brackets, and standard deviation after brackets, for administered activity, CTDI and DLP are presented in Table 1. All examinations were performed with 18F-2-fluoro-2-deoxy-D-glucose (FDG). Two types of examinations were performed. The most common type, named here ‘standard examination’, included head and body till mid thighs. The second examination, named ‘whole-body examination’, involved scanning of the whole body, including head, till feet. The whole-body examination was performed for a small number of patients with diagnosis melanoma malignum. The main technical parameters used in the CT protocols are presented in Table 2. Automatic exposure control (AEC) denotes that tube current modulation
# The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
PATIENT DOSES FROM PET-CT Table 1. The number of patients, administered activity, CTDI and DLP per type of examination and system. Examination
Standard Whole body
PET-CT system
No. of patients
Amean (min., max.); SD (MBq)
CTDImean (min., max.); SD (mGy)
DLPmean (min., max.); SD (mGy cm)
I II I II
43 52 7 6
258 (185, 418); 56 313 (153, 511); 73 258 (185, 418); 55.8 313 (153, 511); 73
5.9 (4.2, 8.5); 1 5.4 (1.8, 11.1); 2 6.2 (4.2, 8.5); 1.4 3.7 (2.3, 4.6); 1
591 (395, 1012); 130 575 (194, 1242); 248 1112 (712, 1581); 285 620 (428, 811); 166
Mean values are presented, minimum and maximum values in parentheses and standard deviation (SD). Table 2. Main technical parameters used for CT scanning. Examination
Standard Whole body
PET-CT system
kV
Rotation time (s)
Slice thickness (no. of rows`mm)
Pitch
AEC/mean mA s
I II I II
120 120 120 120
0.5 not provided 0.5 not provided
16` 1.5 3.75 16` 1.5 3.75
0.69 not provided 0.69 not provided
AEC/84 AEC/not provided AEC/89 AEC/not provided
AEC, automatic exposure control.
is used. The same protocol for both types of examinations was used to perform CT with System I. For System II, the whole-body examination was performed with lower-dose protocol, which can be seen from the lower CTDI values (Table 1, mean CTDI 5.4 mGy for the standard and 3.7 mGy for the wholebody exam on II). The activities of RF administered to patients depended on the patient body mass and not on the type of examination. The calculated effective doses are presented in Figures 1 and 2 for standard and whole-body examinations, respectively, in the following order: first column is E from CT derived applying the NRPB method (only in Figure 1), the second column is E with CT Expo and ICRP 60 tissue weighting factors, the third column is E with CT Expo and ICRP 103 tissue weighting factors, the fourth is the PET contribution to E and the fifth is total effective dose from the PET-CT examination, taking into account the CT contribution calculated with CT Expo and ICRP 103. The conversion coefficient for the trunk region was used with the NRPB method for the standard examination(4). This is probably the reason for the higher value of E obtained with this method, compared with CT Expo, because the real scanned anatomic region included much longer part of the body than only trunk. This led to higher DLP values and hence E. CT contribution of 8.9 mSv was found for System I with the NRPB method, compared with 8.0 and 7.8 mSv with CT Expo and ICRP 60, and CT Expo and ICRP 103, respectively (Figure 1). CT contribution of 8.7 mSv was calculated with the NRPB method for System II, and 7.8 and 7.7 mSv with CT Expo and
Figure 1. Effective doses for the standard PET-CT examination for Systems I and II. The first column shows E in millisievert from CT component, calculated with NRPB conversion coefficients; the second column shows E calculated with CT Expo applying ICRP 60 tissue weighting factors; the third column shows E with CT Expo applying ICRP 103 factors; the fourth column shows E from the PET component and the fifth shows E from the whole examination, taking into account CT contribution with CT Expo and ICRP 103.
ICRP 60, and CT Expo and ICRP 103, respectively. It should be taken into account that the NRPB coefficients are published for ICRP 60 tissue weighting factors(4). The effective doses from CT for the standard exam are comparable for both systems, with differences entirely within the uncertainty of the methods. However, higher activities of radiopharmaceuticals (Table 1) were observed for System II, resulting in higher PET contribution to E (4.9 mSv for System I vs. 5.9 mSv for System II). The reason is that System I has the time-of-flight option, not present
431
S. AVRAMOVA-CHOLAKOVA ET AL.
Figure 2. Effective doses the whole-body PET-CT examination for Systems I and II. The first column shows E in millisievert from CT component, calculated with CT Expo applying ICRP 60 tissue weighting factors; the second column shows E with CT Expo applying ICRP 103 factors; the third column shows E from the PET component and the fourth shows E from the whole examination, taking into account CT contribution with CT Expo and ICRP 103.
at System II. It allows lower activities to be used without compromising image quality(6). The total E for System II was consecutively higher (13.6 mSv), while for System I it was 12.7 mSv for the standard examination. Because of the lower-dose CT protocol used on System II, the CT contribution to the whole-body examination was 5.9 mSv (CT Expo, ICRP 103) versus 9.4 mSv for System I (Figure 2). Consecutively, the total E for System I is higher—14.5 mSv, versus 11.8 mSv for System II, regardless of the higher mean administered activity. Brix et al. reported effective doses from PET-CT examinations in four hospitals in Germany of the order of 24–26 mSv(7). These examinations included a diagnostic CT scan in most cases, and in only some of the hospitals, a low-dose CT was performed. The diagnostic CT was estimated to deliver 14.1– 18.6 mSv, while the low-dose CT was reported to contribute to 1.3 –4.5 mSv. The values for Systems I and II are higher than the latter reported by Brix but much lower than the diagnostic CT values. It should be taken into account in this comparison that the body region scanned reported by Brix had lower limit defined by the symphysis (the gonads receiving only scattered radiation), while all examinations on our systems were in fact whole body. The PET contribution according to Brix is 5.7–7 mSv with 18F-FDG (300 or 370 MBq), which is comparable with or higher than Systems I and II in this study. Huang et al. performed similar study with one PET-CT scanner(8). For the most frequently used CT protocol, they measured about 7 mSv for standard patient, represented by Alderson-Rando phantom.
This value is lower than that calculated in our study, but the phantom used represented 163 cm high and 54 kg weighing human, used for both female and male by removing breast attachments. In this study for System I, the mean height of patients was 167 cm and the mean weight was 73 kg, and correspondingly 169 cm and 74 kg for System II, which can explain the higher values of E. For obese patients, Huang reported effective dose from CT up to about 19 mSv with the same protocol. The PET contribution was 6.2 mSv (using 370 MBq 18F-FDG), similar to or higher than our values. Khamwan et al. reported 14.5 mSv from CT and 4.4 mSv from PET for the same type of examinations, with a total of 18.9 mSv(9). The CT contribution and the total E reported by these authors are higher than those calculated here. Kaushik et al. estimated total effective dose from a typical protocol of whole-body PET-CT examination, 14.4 mSv for females and 11.8 mSv for male patients, from 18F-FDG that is in a good agreement with our results(10). Tonkopi et al. elaborated optimised CT protocol for whole-body PET-CT with a reduction of CT effective dose from 8.1 to 5.5 mSv(11). Similar values are achieved during the whole-body examination with System II. Potential for further dose reduction, especially from CT component, could be investigated on both systems. CONCLUSIONS Estimation of patient doses from PET-CT procedures was performed for the first time in the country. Effective dose for both PET-CT scanners was relatively low or comparable with similar studies, but potential for dose reduction will be further investigated, especially from the CT component. The contribution of CT to the effective dose, calculated with the NRPB conversion coefficients, had higher values, compared with the values calculated with CT Expo. This is probably due to the limitation of the conversion coefficients to the trunk region, while the longer scanning range is taken into account in the software calculation. REFERENCES
432
1. Townsend, D. Combined PET/CT: the historical perspective. Semin. Ultrasound CT MR 29(4), 232–235 (2008). 2. International Commission on Radiological Protection. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60. Ann. ICRP 21, 4– 11 (1991). 3. International Commission on Radiological Protection. The Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37, 61–71 (2007).
PATIENT DOSES FROM PET-CT 4. Shrimpton, P. C. Assessment of patient dose in CT. NRPB-PE/1/2004 (2004). 5. International Commission on Radiological Protection. Radiation dose to patients from radiopharmaceuticals. ICRP publication 80. Ann. ICRP 28, 47– 83 (1998). 6. Fakhri, G., Surti, S., Trott, C., Scheuermann, J. and Karp, J. Improvement in lesion detection with whole-body oncologic time-of-flight PET. J. Nucl. Med. 52, 347– 353 (2011). 7. Brix, G., Lechel, U., Glatting, G., Ziegler, S., Munzing, W., Muller, S. and Beyer, T. Radiation exposure of patients undergoing whole-body dual-modality 18F-FDG PET/CT examinations. J. Nucl. Med. 46(4), 608– 613 (2005).
8. Huang, B., Law, M. and Khong, P. Whole-body PET/ CT scanning: estimation of radiation dose and cancer risk. Radiology. 251(1), 166–174 (2009). 9. Khamwan, K., Krisanachinda, A. and Pasawang, P. The determination of patient dose from 18F-FDG PET/CT examination. Radiat. Prot. Dosim. 141(1), 50–55 (2010). 10. Kaushik, A., Jaimini, A., Tripathi, M., D’Souza, M., Sharma, R., Mishra, A. K., Mondal, A. and Dwarakanath, B. S. Estimation of patient dose in 18F-FDG and 18F-FDOPA PET/CT examinations. J. Can. Res. Ther. 9(3), 477–483 (2013). 11. Tonkopi, E., Ross, A. and MacDonald, A. CT dose optimization for whole-body PET/CT examinations. Am. J. Roentgenol. 201, 257– 263 (2013).
433
