Introduction and Aims: This study examined the feasibility and clinical response of treatment with the Cyberknife Stereotactic Radiosurgery system of patients with spine tumors not amenable to other types of treatment. These included patients with metastases recurrent after previous radiation, those resistant to radiation or those requiring extensive surgery for complete resection.

Method: Twenty-nine patients with tumors of the spine were treated with hypofractionated (one to four fractions) high dose radiation (CyberKnife), delivered using implanted fiducial markers for precise stereotactic localisaton. Patients had either recurrent spinal metastases (19), radio-resistant metastases (seven) or small lesions requiring extensive resection (three). After four to six fiducials were implanted, the patient was immobilised in a custom-moulded cradle and a CT scan was obtained with up to 300 slices at 1.25mm intervals. Inverse plannning was done to minimise dose to critical structures in close proximity to the tumor mass. Patients were followed-up with clinical pain scores, total pain medication, functional assessment and follow-up CT and/or MRI at three-month intervals to assess response to treatment.

Results: The tumors were located in all areas of the spine from C4 to the sacrum, with renal cell carcinoma being the most common diagnosis. The mean tumor volume was 253.4cc, with a range of 0.33 to 678.9 ccs. The maximum radiation dose prescribed to the tumor ranged from 1600cGy to 2500cGy delivered in one to four fractions. The number of fractions was determined by the tumor volume and whether the spinal lesion had been previously treated with radiation. The maximum allowable dose to the adjacent spinal cord was 800cGy and thus for the majority of the tumors prescribed to 2500cGy, 80% of the tumor volume received at least 2000cGy. Patients were treated in an outpatient setting with an average treatment time of 75 minutes. There were no new neurologic deficits or acute radiation toxicity. Patients with lesions in the lumbar spine or sacrum often experienced a brief period of nausea, which was easily controllable with one dose of anti-emetic. Some patients experienced a period of malaise or lethargy with no predictive factors. Pain was markedly improved in all patients with metastatic disease as demonstrated by pain scores, decreased use of narcotic medications and improved function. Repeat radiographic studies at three months generally demonstrated stable tumor volume, while those at six months showed decrease in tumor size.

Conclusion: Stereotactic radiosurgery has distinct advantages over external beam for patients with tumors of the spine, including less toxicity, ability to treat recurrences in previously radiated fields, and shorter treatment durations. While GammaKnife for cranial lesions is a widely accepted technique by neurosurgeons, the use of frameless stereotactic radiosurgery with the Cyberknife is new to the armamentarium of orthopaedic surgeons treating spinal tumors.