Pediatric dose assessment in combined 18F (FDG) PET/CT procedures

The fast growing use of hybrid Positron Emission Tomography (PET) combined with Computed Tomography (CT) in diagnosis has proven to provide more accurate diagnostic information on cancer diseases. This is true for both adult and pediatric patients because of the ability for CT to give anatomic information supporting the metabolic information obtained from PET. Although the practice of using PET/CT is found to give clinical benefits, concerns on the doses delivered to pediatric patients continue to rise because of limited data. At King Faisal Specialist Hospital, Riyadh, Saudi Arabia, PET/CT was introduced in the year 2006. PET procedures are performed using 18F fluorodeoxyglucose (FDG) and CT scanning is performed using 80 kVp, 75 mA, 1.675:1 pitch and scan length from mid brain to mid thigh. For ages 14 and 15 years old, the kVp and mAs are 140 and 100 respectively. This study aims to provide data on effective doses to pediatric patients for PET/CT procedures which could contribute to the establishment of reference dose levels. It is also aimed to investigate possible means to reduce pediatric doses to limit the risks of exposures. A total of 113 patients were included in the study and were grouped as age 0 (less 1 year old), 1 (1 to less 5 years old), 5 (5 to less 10 years old), 10 (10 to less 14 years old) and 15 (14 to 15 years old). Age groups 5 and 10 years old give the highest percentage of patients (38 and 37% respectively). Results show that CT doses are in the range of 15 to 25% of the PET doses. The combined mean effective dose due to PET and CT is highest for neonates (15.5 mSv) and age group 1 year old (15.9mSv). Studies have shown that low dose CT provides adequate attenuation and does not contribute high noise to PET images. Reducing the mA from 75 to 10 for age groups 0 and 1 will reduce the dose by a factor of 100. (author)