Effective dose estimation for oncological and neurological PET/CT procedures

The aim of this study was to retrospectively evaluate the patient effective dose (ED) for different PET/CT procedures performed with a variety of PET radiopharmaceutical compounds. PET/CT studies of 210 patients were reviewed including Torso ( n = 123), Whole body (WB) ( n = 36), Head and Neck Tumor (HNT) ( n = 10), and Brain ( n = 41) protocols with 18 FDG ( n = 170), 11 C-CHOL ( n = 10), 18 FDOPA ( n = 10), 11 C-MET ( n = 10), and 18 F-florbetapir ( n = 10). ED was calculated using conversion factors applied to the radiotracer activity and to the CT dose-length product. Total ED (mean ± SD) for Torso- 11 C-CHOL, Torso- 18 FDG, WB- 18 FDG, and HNT- 18 FDG protocols were 13.5 ± 2.2, 16.5 ± 4.5, 20.0 ± 5.6, and 15.4 ± 2.8 mSv, respectively, where CT represented 77, 62, 69, and 63% of the protocol ED, respectively. For 18 FDG, 18 FDOPA, 11 C-MET, and 18 F-florbetapir brain PET/CT studies, ED values (mean ± SD) were 6.4 ± 0.6, 4.6 ± 0.4, 5.2 ± 0.5, and 9.1 ± 0.4 mSv, respectively, and the corresponding CT contributions were 11, 14, 23, and 26%, respectively. In 18 FDG PET/CT, variations in scan length and arm position produced significant differences in CT ED ( p < 0.01). For dual-time-point imaging, the CT ED (mean ± SD) for the delayed scan was 3.8 ± 1.5 mSv. The mean ED for body and brain PET/CT protocols with different radiopharmaceuticals ranged between 4.6 and 20.0 mSv. The major contributor to total ED for body protocols is CT, whereas for brain studies, it is the PET radiopharmaceutical.