Operational Radiation Safety Considerations During Equine Superficial Radiation Treatment Using Portable X-Ray...

Veterinary personnel exposure due to scattered x rays, when present during superficial radiation treatment (SRT), was evaluated. Veterinary personnel presence is needed during SRT to minimize the degree of required aesthesia to horses. Animal treatment was simulated, and exposure rates determined for 50, 70, and 100 kV x rays using eight different SRT applicators. Exposure rates at the surface of a solid water phantom (SWP) phantom ranged from 3.9 mR h-1 to 396 mR h-1 for 50 kV, from 41 mR h-1 to 2,880 mR h-1 for 70 kV, and from 235 mR h-1 to 7,500 mR h-1, for 100 kV, respectively. A horse phantom was used to mimic SRT equine ocular treatment creating a spatial exposure field where the directional scatter was measured at 1 m. The minimum distance away from the source to reach < 2 mR h-1 varied with angular position and energy and was lowest for all energies directly behind the x-ray tube. The closest distance before exceeding 2 mR h-1 at 50 kVp was determined to 1.96 m. A worker could stand 1 m behind the x-ray tube at 50 kVp with 0.25 mm lead for 15,106 hours. Typical SRT treatment times for horse eyelid squamous cell carcinoma are less than 5 minutes, and radiation doses to practitioners are expected to be well below local administrative ALARA limits.