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Purpose The phase II component of RTOG 0631 assessed the feasibility and safety of spine radiosurgery (SRS) for localized spine metastases in a cooperative group setting. Materials and Methods Patients with 1-3 spine metastasis with a Numerical Rating Pain Scale (NRPS) score ≥ 5 received 16 Gy single fraction SRS. The primary endpoint was SRS feasibility: image-guidance RT (IGRT) targeting accuracy ≤ 2mm, target volume coverage > 90% of prescription dose, maintaining spinal cord dose constraints (10 Gy to ≤ 10% of the cord volume from 5-6mm above to 5-6mm below the target or absolute spinal cord volume < 0.35cc) and other normal tissue dose constraints. A feasibility success rate < 70% was considered unacceptable for continuation of the phase III component. Based on the one-sample exact binomial test with α=0.10 (1-sided), 41 patients were required. Acute toxicity was assessed using the National Cancer Institute Common Toxicity Criteria for Adverse Events, version 3.0. Results Sixty-five institutions were credentialed with spine phantom dosimetry and IGRT compliance. Forty-six patients were accrued, and 44 were eligible. There were 4 cervical, 21 thoracic and 19 lumbar sites. Median NRPS was 7 at presentation. Final pre-treatment rapid review was approved in 100%. Accuracy of image-guided SRS targeting was in compliance with the protocol in 95%. The target coverage and spinal cord dose constraint were in accordance with the protocol requirements in 100% and 97%. Overall compliance for other normal tissue constraints was per protocol in 74%. There were no cases of grade 4-5 acute treatment-related toxicity. Conclusion The phase II results demonstrate the feasibility and accurate use of SRS to treat spinal metastases, with rigorous quality control, in a cooperative group setting. The planned RTOG 0631 phase III component will proceed to compare pain relief and quality of life between SRS and external beam radiotherapy.

BACKGROUND Radiosurgery can deliver a single, large radiation dose to a localized tumor using a stereotactic approach and hence, requires accurate and precise delivery of radiation to the target. Of the extracranial organ targets, the spine is considered a suitable site for radiosurgery, because there is minimal or no breathing‐related organ movement. The authors studied spinal radiosurgery in patients with spinal metastases to determine its accuracy and precision. METHODS The spinal radiosurgery program was based on an image‐guided and intensity‐modulated, shaped‐beam radiosurgical unit. It is equipped with micromultileaf collimators for beam shaping and radiation intensity modulation and with a noninvasive, frameless positioning device that uses infrared, passive marker technology together with corroborative image fusion of the digitally reconstructed image from computed tomography (CT) simulation and orthogonal X‐ray imagery at the treatment position. These images were compared with the port films that were taken at the time of treatment to determine the accuracy of the isocenter position. Clinical feasibility was tested in 10 patients who had spinal metastasis with or without spinal cord compression. The patients were treated with fractionated external beam radiotherapy followed by single‐dose radiosurgery as a boost (6–8 grays) to the most involved portion of the spine or to the site of spinal cord compression. RESULTS The accuracy for the isocenter was within 1.36 mm ± 0.11 mm, as measured by image fusion of the digitally reconstructed image from CT simulation and the port film. Clinically, the majority of patients had prompt pain relief within 2–4 weeks of treatment. Complete and partial recovery of motor function also was achieved in patients with spinal cord compression. The radiation dose to the spinal cord was minimal. The maximum dose of radiation to the anterior edge of the spinal cord within a transverse section, on average, was 50% of the prescribed dose. There was no acute radiation toxicity detected clinically during the mean follow‐up of 6 months. CONCLUSIONS Image‐guided, shaped‐beam spinal radiosurgery is accurate and precise. Rapid clinical improvement of pain and neurologic function also may be achieved. The results indicate the potential of spinal radiosurgery in the treatment of patients with spinal metastasis, especially those with solitary sites of spine involvement, to increase the prospects of long‐term palliation. Cancer 2003;97:2013–8. © 2003 American Cancer Society. DOI 10.1002/cncr.11296