Skeletal malignancies among beagles injected with 241Am

Area of Science:

• Radiobiology
• Oncology
• Toxicology

Background:

• Skeletal malignancies, particularly osteosarcomas, represent a significant health concern.
• Understanding the dose-response relationship of radioactive isotopes is crucial for risk assessment.
• Beagles have been utilized as a model for studying long-term effects of internally deposited radionuclides.

Purpose of the Study:

• To determine the dose-response relationship for skeletal malignancies induced by Americium-241 (Am-241) in beagles.
• To compare the bone-cancer-inducing effectiveness of Am-241 relative to Radium-226 (Ra-226).

Main Methods:

• 117 beagles were injected with graded doses of Am-241 (0.07 to 104 kBq kg-1) and observed for their lifetime.
• Skeletal radiation doses were calculated to 1 year prior to death to estimate tumor growth initiation.
• Mathematical expressions were derived to describe the percent occurrence of bone sarcoma as a function of skeletal dose for both Am-241 and Ra-226.

Main Results:

• A linear dose-response relationship was observed for Am-241: A = 0.76 + 30D (for D < 3 Gy), where A is the percent of dogs with skeletal malignancy.
• For Ra-226, the relationship was A = 0.76 + 4.7D (for D < 20 Gy).
• The ratio of coefficients indicated that Am-241 is approximately 6 ± 0.8 times more effective than Ra-226 at inducing bone cancer at low doses.

Conclusions:

• Americium-241 demonstrates significantly higher potency for bone cancer induction compared to Radium-226 in this canine model.
• The findings provide valuable data for refining radiation protection standards and risk assessments for Am-241 exposure.
• Further research may explore the mechanisms underlying the differential effectiveness of these radionuclides.