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Bone Loss Following Proton Irradiation.  E.R. Bandstra¹, M.J. Pecaut², E.R. Anderson¹, J.S. Willey¹, F. De Carlo³, S.R. Stock⁴, D.S. Gridley², G.A. Nelson², T.A. Bateman^{1    1}Dept. of Bioengineering, Clemson Univ., Clemson, SC, ²Dept. of Radiation Medicine, Loma Linda Univ., Loma Linda, CA, ³Advanced Photon Source, Argonne National Laboratory (ANL), Argonne, IL, ⁴Dept. of Molecular Pharmacology and Biological Chemistry, Northwestern University, Chicago, IL.

On long-duration exploratory missions, astronauts will likely be exposed to higher doses of proton radiation from solar particle events (SPE) than experienced on ISS. We have previously demonstrated that 2 Gy of proton radiation has a negative effect on trabecular bone. This study aims to investigate the effects of lower doses of proton radiation, similar to what an astronaut may be exposed to from an SPE. Female C57BL/6J mice were exposed to a 0, 0.5, 1, or 2 Gy dose of acute, whole-body proton radiation, and euthanized 120 days post-exposure. Trabecular bone in the proximal tibiae was analyzed using microCT (Scanco 20, 9 micron voxel size). Cortical bone was analyzed using microCT on the tibia (tibular-fibular junction) and the femur (mid-diaphysis and third trochanter). Consistent with previous study, mice receiving 2 Gy of radiation showed a significant decline in trabecular bone volume fraction (19.8%), trabecular number (9.0%), apparent density (18.8%), and an increase in trabecular spacing (11.3%). Mice exposed to 1 Gy of radiation also had a non-significant decline in trabecular bone volume fraction (12.7%). Further examination of the 1 Gy group using high resolution synchrotron microCT (ANL, 2.66 micron voxel size) revealed a significant decline in trabecular volume fraction (13.3%). No changes were observed in 0.5 Gy mice. No change was perceived in cortical porosity or polar moment of inertia. This study indicates that doses as low as 1 Gy have negative effects on trabecular bone and seem to have no effect on cortical bone. (Supported by NASA GSRP, SC Space Grant, Procter & Gamble, NSBRI (NASA NCC9-58), and NASA NAG 9-1499. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357