Low level irradiation in mice can lead to enhanced trabecular bone morphology

Charged particle radiation such as iron ions and their secondary fragmentation products are of particular concern to the skeleton due to their high charge and energy deposition. However, little is known about the long-term effects of these particles on trabecular and cortical bone morphology when applied at relatively low levels. We hypothesized that even a 4.4 cGy dose of a complex secondary iron ion radiation field will compromise skeletal quantity and architecture in adult mice. One year after radiation exposure and compared to age-matched controls, 4.4 cGy irradiated mice had 51 % more trabecular bone, 56 % greater trabecular bone volume fraction, 16 % greater trabecular number, and 17 % less trabecular separation in the distal metaphysis of the femur. Similar to the metaphysis, trabecular bone of the distal femoral epiphysis in 4.4 cGy mice had 33 % more trabecular bone, 31 % greater trabecular bone volume fraction, and a 33 % smaller structural model index. Cortical bone morphology, whole bone mechanical properties, and lower leg muscle mass were unaffected. When compared to two additional groups, irradiated at either 8.9 or 17.8 cGy, a (negative) dose response relationship was observed for trabecular bone in the metaphysis but not in the epiphysis. In contrast to our original hypothesis, these data indicated that a secondary field of low-level, high-linear energy transfer iron radiation may cause long-term augmentation, rather than deterioration, of trabecular bone in the femoral metaphysis and epiphysis of mice.