Whole-body PET/CT Scanning: Estimation of Radiation Dose and Cancer Risk

Purpose: To estimate the radiation dose from whole-body fluorine 18 ((18)F)-fluorodeoxyglucose (FDG) positron emission tomographic (PET)/computed tomographic (CT) studies and to evaluate the induced cancer risk to U.S. and Hong Kong populations.

Materials And Methods: Fluorine 18-FDG PET/CT studies obtained by using a 64-detector CT unit and one of three CT protocols were evaluated. CT protocol A consisted of 120 kV; rotation time, 0.5 second; pitch, 0.984; 100-300 mA; and noise level, 20. CT protocol B was the same as A, except for a fixed tube current of 250 mA. CT protocol C consisted of 140 kV; rotation time, 0.5 second; pitch, 0.984; 150-350 mA; and noise level, 3.5. CT doses were measured in a humanoid phantom equipped with thermoluminescent dosimeters. Doses from (18)F-FDG PET scanning were estimated by multiplying the (18)F-FDG radioactivity (370 MBq) with dose coefficients. Effective doses were calculated according to International Commission on Radiological Protection publication 103. Lifetime attributable risk (LAR) of cancer incidence was estimated according to the National Academies' Biological Effects of Ionizing Radiation VII Report.

Results: Effective doses with protocols A, B, and C, respectively, were 13.45, 24.79, and 31.91 mSv for female patients and 13.65, 24.80, and 32.18 mSv for male patients. The LAR of cancer incidence associated with the dose was higher in the Hong Kong population than in the U.S. population. For 20-year-old U.S. women, LARs of cancer incidence were between 0.231% and 0.514%, and for 20-year-old U.S. men, LARs of cancer incidence were between 0.163% and 0.323%; LARs were 5.5%-20.9% higher for the Hong Kong population. The induced cancer risks decreased when age at exposure increased.

Conclusion: Whole-body PET/CT scanning is accompanied by substantial radiation dose and cancer risk. Thus, examinations should be clinically justified, and measures should be taken to reduce the dose.