BACKGROUND.Spine radiosurgery causes a rapid dose fall‐off within the spinal cord. The tolerance of partial volume of the spinal cord may determine the extent of clinical application. The study analyzed the partial volume tolerance of the human spinal cord to single fraction radiosurgery.METHODS.A total of 230 lesions with spine metastases in 177 patients were treated with radiosurgery with single fraction of 8 to 18 Gy, prescribed to the 90% isodose line that encompassed the target volume. Spinal cord volume was defined as 6 mm above and below the radiosurgery target volume. Spinal cord dose was calculated from the radiation dose/spinal cord volume histogram and correlated with clinical/neurological status and radiographic studies. Median follow‐up was 6.4 months (range, 0.5–49 months). The 1‐year survival rate was 49%.RESULTS.The average spinal cord volume defined at the treated spinal segment was 5.9 ± 2.2 mL. The average dose to the 10% spinal cord volume was 9.8 ± 1.5 Gy, calculated from the dose‐volume histogram in the group of 18 Gy prescribed dose. The spinal cord volume that received higher than 80% of the prescribed dose was 0.07 ± 0.10 mL, which represented 1.3 ± 1.8% of the cord volume. Among the 86 patients who survived longer than 1 year there was 1 case of radiation‐induced cord injury after 13 months of radiosurgery. There were no other cases of spinal cord sequelae.CONCLUSIONS.Whereas the maximum spinal cord tolerance to single‐dose radiation is not known, partial volume tolerance of the human spinal cord is at least 10 Gy to 10% of the spinal cord volume defined as 6 mm above and below the radiosurgery target. Cancer 2007;109:628–636. © 2006 American Cancer Society.

Precision and accuracy of image-guided spinal radiosurgery has been previously demonstrated. This study was carried out to determine the clinical efficacy of spine radiosurgery for the treatment of solitary spinal metastases with or without cord compression. A total of 49 patients with 61 separate spinal metastases were treated with radiosurgery. All patients had pathologically proven primary cancers and had either synchronous or metachronous metastasis to the spine. The majority of the patients presented with back pain. All patients received single-dose radiosurgery to the involved spine only. The radiosurgery dose ranged from 10 to 16Gy. The primary endpoint was pain control, but outcomes in neurological status and radiological tumor control also were assessed. The median time to pain relief was 14 days and the earliest time of pain relief was within 24hours. Complete pain relief was achieved in 46%, partial relief in 18.9%, and stable symptoms in 16.2%. Relapse of pain at the treated spinal segment was 6.9%. Median duration of pain relief at the treated spine was 13.3 months. Overall pain control rate for one year was 84%. This experience demonstrates that spinal radiosurgery can achieve rapid and durable pain relief. Single-dose radiosurgery has a potential to be a viable treatment option for single spinal metastasis.

This study is to demonstrate the technical and clinical experience of applying image guided spinal radiosurgery for treatment of localized spinal metastasis. A dedicated shaped beam radiosurgery unit with intensity modulated radiotherapy (IMRT) and x-ray based image-guid-

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