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

Overview

• This study measured radiation exposure levels from horses during bone scintigraphy to understand how distance and time affect radiation doses, aiming to provide safety guidelines for workers and recommended isolation times after the procedure.

Introduction and Background

• Bone scintigraphy is a diagnostic imaging technique used in equine orthopedics to detect bone abnormalities by injecting a radiotracer (Tc-methylene diphosphonate).
• The procedure involves exposure to radiation, which poses occupational risks to veterinary staff and requires regulatory measures, including isolation of horses to limit public or personnel exposure post-procedure.
• Despite widespread use, clear data quantifying radiation exposure around treated horses and evidence-based isolation period recommendations remain limited.

Study Objectives

• To quantify radiation dose rates emitted from various anatomical regions of horses following bone scintigraphy.
• To evaluate how radiation exposure changes with varying distances (spatial factor) and over time (temporal factor) post-injection.
• To formulate evidence-based recommendations on occupational safety measures and the duration of mandatory post-scintigraphy isolation periods.

Methods

• Study Design: Prospective, cross-sectional approach involving twenty warmblood horses undergoing musculoskeletal scintigraphy.
• Procedure: Intravenous administration of Tc-methylene diphosphonate at a dosage of ~10 MBq/kg.
• Measurement Points: Radiation dose rates (μSv/h) measured at three anatomical sites – the head, kidney, and pelvic regions.
• Distance Parameters: Dose rates recorded at three distances from horse’s skin: 5 cm, 30 cm, and 100 cm.
• Timeframe: Radiation levels were measured repeatedly from 5 minutes up to 72 hours after injection.

Key Results

• At 5 minutes post-injection and 5 cm distance:
  • Kidney region showed 38% higher radiation dose rates compared to the head region (statistically significant with p=0.001).
  • Pelvic region showed significantly lower dose rates than the head (reduction of 28.2%-55.5%, p < 0.05).
• Effect of Increasing Distance:
  • When distance increased from 5 cm to 30 cm and 100 cm, radiation exposure reduced by 65%-82%.
  • This distance-related reduction was more effective in lowering radiation dose than the natural decay of radioactivity over time alone (p < 0.05).
• Effect of Time:
  • Radiation dose rates at 5 cm decreased significantly over time—falling to ≤45 μSv/h at 6 hours post-injection.
  • By 18 hours post-injection, dose rates dropped further to ≤7.5 μSv/h across all regions measured.

Discussion and Implications

• The highest radiation exposure was detected near the kidney region shortly after injection, likely reflecting tracer uptake and concentration there.
• Spatial distancing is highly effective for radiation protection; maintaining at least 30 cm distance drastically reduces occupational exposure.
• Time also plays a critical role, with natural radioactive decay reducing dose rates significantly within hours post-injection.
• Risks might vary with pathological tracer uptake (e.g., due to bone disease) which could lead to localized areas of increased radiation emission.
• The study primarily included warmblood horses and relatively young animals; older horses often require higher dosages, which may influence dose rates and isolation guidelines.

Conclusions and Recommendations

• Occupational Safety:
  • Veterinary personnel should maintain a minimum distance of 30 cm from horses undergoing bone scintigraphy to substantially lower radiation exposure.
• Post-Scintigraphy Isolation Period:
  • Data supports shortening the isolation period to 6 hours to comply with German radiation safety regulations.
  • To meet international standards, an isolation period of approximately 18 hours is recommended to allow dose rates to drop to safer levels.

Limitations and Considerations

• The influence of disease states causing altered or pathological tracer distribution was not fully explored.
• Findings may be less applicable to older horses or patients receiving higher radiotracer doses, which could elevate radiation exposure risks.