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Characterization of X-ray transmission and scattering during equine radiology procedures at the Johnson Family Equine Hospital


Personnel handling radioactive materials or radiation-emitting devices are at risk of exposure to ionizing radiation, directly from primary beams and indirectly from scattered beams. Hence, radiation workers are enrolled in a radiation dosimetry program to comply with regulations and effectively track exposures. Because X-ray radiation is used daily for diagnostics and therapeutics of animals at the Veterinary Teaching Hospital (VTH) of the Colorado State University (CSU), the Radiation Control Office (RCO) at CSU monitors the workers' radiation dose monthly to ensure safety and compliance. The RCO has set an ALARA Level 1 investigation at 150 millirems (mrem) in a month to keep doses As Low As Reasonably Achievable (ALARA). Personnel exceeding 150 mrem in a month are notified, and the dose is investigated. An investigation level of 150 mrem provides an opportunity for the RCO to intervene early and is low compared to the regulatory annual dose limit of 5000 mrem per year. Over the course of the last few years, the ALARA Level 1 has been exceeded on various occasions by radiology technicians at the Johnson Family Equine Hospital (JFEH), which is affiliated with the VTH at CSU. This project was designed to bridge a substantial knowledge gap regarding the procedures conducted at the JFEH, associated radiation doses, and the facility's suitability for large-animal veterinary applications. This experiment design characterizes the facility and anticipates radiation exposures across various spatial points within the radiology areas, facilitating the identification of radiation exposure hotspots. This study started with staff interview, comprehensive analysis of the daily diagnostic imaging procedures at the JFEH and cross-referencing months with elevated exposure to images. Radiation exposures in the primary beam were modelled for all Technique Factors (TFs) at various distances using SpekCalc® software generated photon fluence energy spectra. The output spectrum data were entered into an MCNP® model for dose assessment using effective dose conversion coefficients. The benchmarked outcome for Cesium-137 differed 3% from the theoretical value. An MCNP® model was used to replicate the direct measurements conducted at 1 meter. The results were consistent with exposure measured by a Biomedical Fluke 451P ionization chamber, previously published exposure measurement for the given kVp and mAs, the calculated exposure for X-ray using kVp and mAs, and the typical effective radiation dose from diagnostic X-ray published by NCRP 160. Finally, another simulation was conducted to recreate the conditions within the radiology facility using phantoms. This simulation facilitated the quantification of effective doses across various spatial points. The simulated absorbed dose was highest in the primary beam, then directly behind the X-ray source, and lowest at a 90-degree angle from the direction of the beam, at the same distance from the source. The absorbed dose also differed considerably in front of and behind the phantom due to photoelectric absorption. After analyzing data, to measure dose accurately, two dosimeters are recommended, one inside and one outside the lead vest. Absorbed dose can be minimized by avoiding primary beam exposure and standing behind the X-ray tube while operating the handheld X-ray switch.


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