Radiation exposure to personnel during portable fluoroscopic imaging of equine lower limbs
Radiation exposure rates were mapped in 4 directions around the suspended c-arm of a portable fluoroscopy unit, while imaging the fetlocks, carpi and tarsi of equine cadaver limbs. Exposure rates were highly dependent on distance and direction relative to the c-arm, and were consistently highest on the tube side. Maximum exposure rates ranged from 2.3 to 59.5 mSv/h among the 3 joints. Radiation exposure fell rapidly with increasing distance from the c-arm, but remained significantly above background levels until approximately 4.7 m, depending on direction (range, 2.7 to 9.9 m). During examinations of the same joints in live horses, exposure rates to the fluoroscopist (thyroid region, tube and image-intensifier hands) and the assistant (thyroid region) were measured. The exposure rate was consistently highest at the fluoroscopist's tube hand (56.2 mSv/h). During a typical fluoroscopic examination of the carpus, radiation exposure to the fluoroscopist's thyroid area and hands was approximately 25 and 40 times greater, respectively, than that previously reported for a comparable radiographic study. Exposure to the assistant was approximately 30 times greater than similar radiography. By observing an experienced fluoroscopist in practice, mean imaging times for routine examinations of the fetlock, carpus and tarsus were determined. Radiation exposure to the fluoroscopist and the assistant, per examination (reported above) and over a conservatively based 40-week working year, was estimated using the previously determined exposure rates. Annual exposure to the assistant's thyroid, and the fluoroscopist's thyroid, image-intensifier hand and tube hand were 11, 47, 187 and 1082 mSv, respectively. Recommended maximum permissible doses (MPD) of radiation are: 20 mSv/year, averaged over 5 years and not exceeding 50 mSv in any given year, to the whole body (estimated by thyroid exposure); and 500 mSv/year to extremities. Portable fluoroscopic imaging of equine lower limbs clearly represents a significant radiation-safety hazard. There is no "safe" distance from the c-arm for personnel within the same room. Radiation-safety procedures during fluoroscopy are just as, if not more, important than during standard radiography. Annual MPD will be rapidly exceeded if radioprotective clothing, which is required by law, is not worn.