The feasibility of radiosurgery for spine metastasis has been demonstrated by a phase I clinical trial, which reported an acceptable safety and targeting accuracy at 1 mm. Subsequent clinical trials reported that spine radiosurgery provides rapid and durable pain control and local tumor control in over 90% of the patients with spine metastasis. Based on this finding, RTOG 0631 phase III clinical trial is ongoing to compare the effectiveness of pain relief and local tumor control by spine radiosurgery compared to cEBRT, under stringent quality assurances. Since the spinal cord is the dose-limiting normal tissue and the radiation dose gradient occurs within the spinal cord with radiosurgery, PI has reported the partial volume tolerance of the spinal cord (as opposed to the entire spinal cord diameter) to be 10 Gy to the 10% of spinal cord volume, which is defined as the volume from 6 mm above to 6 mm below the spinal target volume. This partial volume translated to 0.35 cc absolute volume of the spinal cord. Currently, spine radiosurgery is widely used for treatment of spine metastasis.
Spine radiosurgery has been also tested for treatment or malignant spinal cord compression. Previosuly the standard treatment of spinal cord compression was surgical resection and external beam radiotherapy. A prospective study of radiosurgery for spinal cord compression demonstrated excellent spinal cord decompression and neurological improvement by radiosurgery alone. Spine radiosurgery was used for patients with intact neurological status and/or mild deficit with motor strength. The overall rate of thecal sac decompression and neurologic improvement or preservation was over 80% after radiosurgery. These experiences indicate that radiosurgery can be safely used for patients with spinal cord compression with minimal neurological symptoms or ambulatory (who can safely wait for radiosurgery response), while surgical decompression is indicated in patients with overt neurological deficit (who needs immediate decompression). This is really a practice-changing paradigm.