Characterizing canine dose from external beam irradiation

Abstract

Absorbed dose from Computed Tomography (CT) is a major concern on an individual basis as well as for the collective population due to increased frequency of and dependency on CT scans for diagnostic and therapeutic imaging. Colorado State University recently integrated a large bore multi-slice Positron Emission Tomography and Computed Tomography (PET/CT) scanner into the Veterinary Teaching Hospital. The new PET/CT and high volume of canine CT imaging exams provides a unique opportunity for research into canine organ dose that compliments efforts aimed at characterizing human CT dose. This retrospective study focuses on characterizing the internal dose to a canine brain from a CT scan to a canine body. Organ specific doses were directly measured using an ion chamber placed within a physical canine anatomic phantom. Since dogs have been shown to be a valuable translational model for human radiation effects, accurate estimation of canine CT dose may permit future deterministic and stochastic radiobiological effect studies to be performed with canines on a much shorter time scale than similar studies with humans. Equivalent doses were calculated with a mean (± standard deviation) of 12.96 (± 0.45) mSv, 32.80 (± 0.77) mSv, and 49.24 (± 0.87) mSv for 90, 120 and 140 kVp respectively at a fixed 300 mAs in the brain of the canine phantom. Additionally, these data were fit to a parallel set of human expected doses to the brain of a ten year old child and an adult. The dog data was found to be a good fit to the child data. It was concluded that a dog most closely fits a ten year old child for dose comparisons from CT procedures. The dose comparisons from scattered radiation require more data collection and analysis to best characterize the relationship. Preliminary analysis of scattered radiation to the brain from a chest scan also indicates the child is the best fit for a dose comparison with the canine phantom.