Dose evaluation to patients from different 18F-FDG PET/CT protocols

Objectives Dose to patients from PET/CT protocols depends on internal irradiation from 18F-FDG administration and on external irradiation from CT scan. Total dose to patients was calculated or in vivo measured in 6 different type of PET/CT protocols. Internal and external contributions were compared as a function of the type of investigation and of the CT scan parameters.

Methods 48 PET/CT examinations were investigated: 9 standard whole body scans, 8 whole body for melanoma, 7 brain, 15 respiratory gated protocols, 1 lung PET/CT with CT perfusion and 8 PET/CT whole body protocols with contrast enhanced CT (CE-CT). Internal effective dose was evaluated according to ICRP publication n° 103 (2007) while external dose was in vivo measured with properly calibrated Gafchromic® XR-RV2 films or calculated with CT-Expo V 1.5 (2005) tool for dose evaluation in computed tomography and with ImPACT CT patient dosimetry calculator V 1.0.2 (2009).

Results Total effective dose in mSv was: 11.5 in whole body examinations, 10.8 in melanoma whole body, 5.5 in brain, 16.7 in one bed and 22.2 in two beds respiratory gated exams, 33.1 in PET/CT with CT perfusion and 21.8 in PET/CT whole body exams with CE-CT. The contribution of 18F-FDG administration was: 48% in standard whole body examinations, 52% in melanoma whole body, 87% in brain, 31% in one-bed and 24% in two-beds respiratory gated exams, 17% in PET/CT with CT perfusion and 24% in whole body exams with CE-CT.

Conclusions Total effective dose to patients undergoing PET/CT examination may vary from 5.5 mSv to 33.1 mSv depending on the type of protocol applied. The contribution of the internal effective dose is quite the same in absolute value but it may greatly change as a percentage of the total effective dose. Optimization of acquisition protocols is a key step in reducing dose to patients