Background: Positron emission tomography/computed tomography (PET/CT) has been used as a noninvasive imaging method to assess the disease extent in patients.
Objective: To assess the effective radiation dose in patients who underwent PET/CT.
Materials and Methods: The present study included 24 patients with cholangiocarcinoma (CCA) or hepatocellular carcinoma (HCC), aged 39 to 74 years, who underwent 11C-choline and 18F-FDG whole body PET/CT scans at National Cyclotron and PET Centre, Chulabhorn Hospital. The radiation absorbed doses to target organs and effective whole body doses were calculated from ICRP 106 publication for 18F-FDG and the US FDA publication for 11C-choline.
Results: The average whole body effective dose from the 18F-FDG PET scan was 6.81±1.09 mSv and from the CT scan was 12.95±3.33 mSv. For 11C-choline, the effective whole-body dose was 1.90±0.40 mSv from the PET scan and 14.20±3.14 mSv from the CT scan. Our results showed that 11C-choline accumulates mainly in the liver, lungs and stomach, while the accumulation of 18F-FDG is mainly in bladder, lungs and liver.
Conclusion: The results showed that the effective dose from CT modality between 18F-FDG and 11C-choline patients were not significantly different. However, the average effective dose for patients undergoing whole body 18F-FDG PET was 3.6 times higher than with 11C-choline PET.

Keywords: 11C-Choline, 18F-FDG, Effective dose, PET/CT