Alpha-particle doses to cells of the bone remodeling cycle from alpha-particle-emitting bone-seekers: indications of an antiresorptive effect of actinides.

There are indications that alpha-particle-emitting bone-seekers such as plutonium or americium could enhance bone mass by suppressing bone resorption. To assess this possibility, this study calculates doses from alpha-particle emitters to the cells involved in trabecular bone turnover. Alpha-particle energy deposition in tissue from a bone surface source was calculated by Monte Carlo modeling. This was combined with bone surface cellular geometry to yield dose rates to cells during the remodeling cycle. Bone-resorbing osteoclasts receive on average 50 times the dose rate that bone-forming osteoblasts receive. Newly formed bone shields osteoblasts from alpha particles emitted by the buried deposit of alpha-particle emitters. However, at alpha-particle bone-seeking radionuclide intakes known to cause changes in remodeling (about 3700 Bq/kg body weight), the alpha-particle dose to osteoclasts corresponds to an extremely low rate of cell traversals (0.07% per cycle). It is therefore unlikely that perturbation of bone remodeling by alpha-particle bone-seeking radionuclides is directly caused by alpha-particle traversals of remodeling cells; some other indirect mechanism might be involved.