Radiation dose to trabecular bone marrow stem cells from (3)H, (14)C and selected alpha-emitters incorporated in a bone remodeling compartment.

A Monte Carlo simulation of repeated cubic units representing trabecular bone cavities in adult bone was employed to determine absorbed dose fractions evaluated for (3)H, (14)C and a set of alpha-emitters incorporated within a bone remodeling compartment (BRC). The BRC consists of a well-oxygenated vascular microenvironment located within a canopy of bone-lining cells. The International Commission on Radiological Protection (ICRP) considers that an important target for radiation-induced bone cancer is the endosteum marrow layer adjacent to bone surface where quiescent bone stem cells reside. It is proposed that the active stem cells and progenitor cells located above the BRC canopy, the 'BRC stem cell niche', is a more important radiation-induced cancer target volume. Simulation results from a static model, where no remodeling occurs, indicate that the mean dose from bone and bone surface to the 50 microm quiescent bone stem cell niche, the current ICRP target, was substantially lower (two to three times lower) than that to the narrower and hypoxic 10 microm endosteum for (3)H, (14)C and alpha-particles with energy range 0.5-10 MeV. The results from a dynamic model indicate that the temporal alpha-radiation dose to active stem/progenitor cells located in the BRC stem cell niche from the material incorporated in and buried by forming bone was 9- to 111-fold greater than the dose to the quiescent bone stem cell niche. This work indicates that the remodeling portion of the bone surface, rather than the quiescent (endosteal) surface, has the greatest risk of radiation-induced bone cancer, particularly from short-range radiation, due to the elevated dose and the radiosensitizing oxygen effect.