Fracture occurrence from radionuclides in the skeleton

Area of Science:

• Radiological Science
• Toxicology
• Veterinary Medicine

Background:

• Skeletal fractures are a known complication of internal contamination with bone-seeking radionuclides.
• Understanding fracture risk in animal models is crucial for extrapolating human health risks from radionuclide exposure.

Purpose of the Study:

• To assess the incidence of skeletal fractures in beagles exposed to various bone-seeking radionuclides.
• To determine the dose-response relationship for radionuclide-induced fractures.
• To evaluate the significance of fractures as an endpoint for human exposure to bone-seeking radionuclides, particularly plutonium.

Main Methods:

• A retrospective analysis of fracture occurrence in beagles injected with radionuclides (226Ra, 228Ra, 228Th, 239Pu, 90Sr).
• Statistical comparison (Fisher's Exact Test) of fracture rates between exposed groups and controls.
• Regression analysis to identify dose-dependent increases in fracture occurrence.

Main Results:

• Radionuclides 226Ra, 228Ra, 228Th, and 239Pu were associated with increased fracture incidence in specific skeletal sites (ribs, legs, pelvis, mandible, scapulae) at higher doses.
• Significant dose-elevation of fractures was observed for 239Pu (~50 Gy), 226Ra (~140 Gy), 228Ra (~40 Gy), and 228Th (>15 Gy).
• 90Sr citrate did not significantly increase fracture rates, even at high cumulative doses (up to 101 Gy).

Conclusions:

• Fractures occurred at higher doses of certain bone-seeking radionuclides in dogs.
• Due to competing risks, particularly bone malignancy, fractures are unlikely to be a primary concern at lower plutonium exposure levels in humans.
• This study informs risk assessment for occupational and environmental radionuclide exposures.