Conversion factors to derive organ doses for canine subjects undergoing CT examinations.

Although a large number of CT scans are being conducted on small animals, especially in Western countries, little is known of absorbed dose from veterinary CT scans. In the current retrospective analytical study, we estimated the radiation dose delivered to dogs from CT scans with various scan protocols and compared the results with those of human patients. We adopted a total of three computerized canine models with three sizes combined with a computer simulation model of a CT scanner. The eyes of the dog model received the greatest dose, 1.10 mGy/mGy, in the head scan, followed by a brain dose of 0.85 mGy/mGy. In the chest, abdomen-pelvis (AP), chest-abdomen-pelvis, and head-chest-abdomen-pelvis scans, the heart wall (0.93 mGy/mGy), ovaries (0.99 mGy/mGy), lungs (1.12 mGy/mGy), and thyroid (1.23 mGy/mGy) received the greatest organ doses, respectively. The smallest dog model received up to 1.4-fold greater organ doses than the largest dog in both the chest and AP scans. Overall, the medium-size canine model received organ doses comparable to those of the 1-year-old child model in the head scan, the 5-year-old child in chest scan, and the 10-year-old child in AP scan. The organ dose conversion factors derived from this study should help evaluate absorbed dose for canine patients undergoing CT exams.