Abstract
Introduction
Stereotactic radiosurgery has shown great promise in the treatment of metastatic lesions within the spine. However, recent clinical studies have indicated that the procedure may increase the risk of developing vertebral compression fractions, particularly in osteoporotic patients (Rose et al, 2009. J Clinical Onc. 27(29):5075; Boehling et al, 2012. J Neurosurg Spine. 16:379). There is thus a critical need for research examining the effects of focused radiation on bone quality and mechanical properties. We have developed a rabbit model which enables the analysis of the effects of focused radiation on vertebral osteonecrosis, structure, and biomechanical integrity. Using this model, we are testing the hypothesis that fractionation of radiation dosing can reduce radiation osteonecrosis and preserve structural and biomechanical integrity of the spine.
Material and Methods
The L5 vertebral body of New Zealand White (NZW) rabbits was treated, under computerized tomography (CT) guidance, with either a single 24 Gy dose of radiation or three fractionated doses over 3 consecutive days of 8 Gy radiation via the small animal radiation research platform (SARRP) (Wong et al, 2008. Int J Radiat Oncol Biol Phys. 71(5): 1591). Effects of radiation treatment on L2, L4, L5, and L6 vertebral osteonecrosis, structure, and biomechanical integrity were evaluated 6 months postirradiation via high-resolution CT imaging (Skyscan, Bruker, Belgium), histology, and nondestructive biomechanical compression testing and were compared with nonirradiated controls. Vertebral bone volume over total volume (BV/TV), trabecular thickness (Tb.Th.), and trabecular spacing (TB.Sp) were evaluated from CT images via CTAn software (Bruker, Belgium).
Result/Conclusion: Results till date suggest that a localized single dose of 24 Gy radiation leads to loss of vertebral bone volume and trabecular number and a subsequent increase in trabecular spacing. Similarly, hypofractionation of the radiation dose (3 × 8 Gy) leads to reduced trabecular number and increased trabecular spacing, yet preserves normalized bone volume. Whether these changes in bone morphology translate into reduced mechanical integrity is currently under analysis. Future work will utilize this model to evaluate the efficacy of various therapies, such as teriparatide (PTH [1–34]), in the prevention of radiation-induced osteonecrosis.