Targeting of Osseous Sites with -Emitting 223Ra: Comparison with the -Emitter 89Sr in Mice

The bone-seeking property and the potential exposure of red marrow by the -particle emitter 223Ra (half-life, 11.43 d) were compared with those of the -emitter 89Sr (half-life, 50.53 d). Methods: The biodistributions of 223Ra and 89Sr were studied in mice. Tissue uptake was determined at 1 h, 6 h, 1 d, 3 d, and 14 d after intravenous administration. Radiation absorbed doses were calculated for soft tissues and for bone. Multicellu-lar-level doses were estimated for bone marrow cavities. Re-sults: Both 89Sr and 223Ra selectively concentrated on bone surfaces relative to soft tissues. The measured bone uptake of 223Ra was slightly higher than that of 89Sr. At 24 h, the femur uptake of 223Ra was 40.1 % 7.7 % of the administered activity per gram of tissue. The uptake in spleen and most other soft tissues was higher for 223Ra than for 89Sr. Although predominant clearance of 223Ra was observed from the soft tissues within th