Spatial and temporal radiation exposure during equine bone scintigraphy: Implications for occupational safety and post-scintigraphy isolation.

BACKGROUND: Bone scintigraphy is a valuable diagnostic modality in equine orthopaedics, but it is associated with occupational radiation exposure and regulatory requirements for post-procedural isolation. OBJECTIVES: To quantify radiation dose rates emitted from horses undergoing bone scintigraphy, to evaluate the effects of distance (spatial) and time (temporal) on radiation exposure, and to derive evidence-based recommendations for post-scintigraphy isolation periods. STUDY DESIGN: Prospective, cross-sectional study. METHODS: Twenty warmblood horses underwent musculoskeletal scintigraphy following intravenous administration of 99 mTc-methylene diphosphonate (approximately 10 MBq/kg). Radiation dose rates (μSv/h) were measured at the head, kidney, and pelvic regions at distances of 5, 30, and 100 cm from the skin. Measurements were recorded from 5 min up to 72 h post-injection. RESULTS: At 5 min post-injection and 5 cm distance, the kidney region exhibited dose rates 38% higher than the head (p = 0.001; 95% CI = 39.1-101.8), whereas the pelvic region showed significantly lower values (28.2%-55.5% reduction; p < 0.05). Increasing the distance from 5 cm to 30 cm and 100 cm reduced radiation exposure by 65%-82%, representing a greater protective effect than time decay alone (p < 0.05). Across all anatomical regions, dose rates at 5 cm decreased to ≤45 μSv/h by 6 h and to ≤7.5 μSv/h by 18 h post-injection. MAIN LIMITATIONS: Potential effects of pathological tracer uptake and limited representation of older horses requiring higher radiotracer doses. CONCLUSIONS: Maintaining a minimum distance of 30 cm from horses undergoing bone scintigraphy substantially reduces occupational radiation exposure. The post-scintigraphy isolation periods can be shortened to 6 h under German regulations and to approximately 18 h to meet international standards.