Room: Exhibit Hall | Forum 4
Purpose: To determine if rapid bone loss occurs in vertebrae post-irradiation (IR) in order to predict radiation-induced bone injury.
Methods: Sixteen male rhesus macaques non-human primates (NHPs) were analyzed after single fraction total chest IR to a midplane dose of 10 Gy with 6 MV photons. Ages at IR varied from 45 - 134 mo. X-ray computed tomographic scans were taken 2 mo prior to IR and 2, 4, 6 and 8 mo post-IR for all animals. Bone mineral density (BMD) and cortical thickness (CtTh) were calculated longitudinally for thoracic (T9) and lumbar (L2, L4) vertebral bodies.
Results: Greater radiation-induced pulmonary toxicity was noted in NHPs age < 50 mo (N=8) vs NHPs > 50 mo (N=8), p = 0.03. Animals older than 50 mo at IR had a significant loss in CtTh at T9 (in-field) by 2 mo post-IR, p = 0.0009, which persisted to 8 mo. In contrast, no loss of CtTh was observed in vertebrae out-of-field (L2 and L4). Loss of BMD was observed by 4 mo post-IR for T9 and 6 mo post-IR for L2 and L4, p < 0.01. For NHPs younger than 50 mo at IR, both CtTh and BMD decreased at T9, L2 and L4 by 2 mo post-IR, p < 0.05.
Conclusion: Rapid loss of CtTh was observed after single fraction high dose chest IR in NHPs. Younger age at IR was associated with increased pneumonitis as well as greater loss of both BMD and CtTh at both in- and out-of-field vertebrae. Older NHPs exhibited rapid loss of BMD and CtTh for in-field vertebrae, but out-of-field vertebrae only had BMD loss. Bone is sensitive to high dose radiation, and rapid loss of bone structure and density may result in fracture. These data may be translatable to clinical SBRT bone injury models.
Funding Support, Disclosures, and Conflict of Interest: This research was supported, in part, by NIH U19 AI67798, NIH T35 OD010946 and NASA NNX15AB50G.