Vertebral metastases, from lung, breast, prostate, renal and myeloma malignancies, occur in over 100,000 individuals each year in the United States. Growing vertebral tumors cause loss of sensory and motor skills, debilitating pain, and vertebral collapse. External beam radiation therapy (plus steroids) has been proven effective for palliation of skeletal metastases providing pain relief with minimal morbidity.
Clinical radiation dose prescriptions for spinal radiosurgery have been escalated to levels currently accepted in intracranial radiosurgery with the expectation of increasing the durability of tumor control in the spinal column and reducing tumor induced paralysis and pain. Nevertheless, the maximum single-dose radiation treatment a vertebra can tolerate without loss of structural integrity is still unknown and may be exceeded in current prescriptions. The recent increase in dosage has correlated with a rise in late onset vertebral fractures.
This research project in collaboration with researchers at UT Southwestern Medical Center is funded by the National Institute of Neurological Disorders and Stroke, part of the National Institutes of Health. It aims to elucidate the complex effects of modern high dose radiation surgery on the metabolic functions and biomechanical strength of human bone.
Materials and Methods
In this study four Yucatan Minipigs were administered 16 Gy or 18 Gy of radiation using stereotactic radiosurgery (SRS) from their fourth to their seventh cervical vertebra, parallel with the spine and focused on half of the vertebral body. One year after SRS, samples of the irradiated and non-radiated vertebrae were obtained and ultrasound propagation velocity, an indicator of bone elasticity, was measured in the axial and transverse directions.
The results show a marked decrease in the ultrasound velocity as well as in the estimated elastic modulus in the radiated samples. Ultrasound propagation velocity and elastic modulus may be effective indicators of bone toxicity following irradiation.
The results of the research will provide thorough understanding of high dose radiation effects on bone and lead to the formulation of predictive indicators for post radio-surgery fracture risk that will be used by physicians in cancer clinics around the world. Ultimately the outcomes of the research will translate into spine cancer patients receiving the best chance for survival with a pain free, high quality of life. It will also open new avenues of research and treatment of other bone diseases, such as osteoporosis, that affect millions of Americans each year.
This work was partially supported by NIH R01-049517 grant, and by a startup grant form Bobby B. Lyle School of Engineering, SMU, Dallas, TX.