CyberKnife radiosurgery for malignant spinal tumors: characterization of well-suited patients

A prospective interventional case-series study.

To provide clinical results of CyberKnife fiducial-free spinal radiosurgery. The study focused on patients with no more than 2 malignant spinal tumors.

Progress in frameless radiosurgical technology has enabled the application of radiosurgery to the spine. The CyberKnife System has been used extensively for spine radiosurgery. Until recently, the system required metallic fiducial implants for precise target tracking. Fiducial-free spinal radiosurgery with the CyberKnife has recently become possible, but until now clinical results obtained with this method had been limited.

From August 2005 until October 2007, a consecutive series of 102 patients with a total of 134 malignant spinal tumors were selected for single-fraction, fiducial-free CyberKnife radiosurgery (CKRS). The study was limited to patients with a maximum of 2 tumors. Malignant primaries included breast cancer in 23 (22.6%) patients, renal cancer in 20 (19.6%) patients, gastro-intestinal cancers in 12 (11.8%) patients, prostate cancer each in 12 (11.8%) patients, lung cancer in 9 (8.9%) patients, sarcomas in 7 (6.9%) patients. A variety of other malignant tumors were found in 19 (18.6%) patients. Patients with spinal cord compression or evidence of myelopathy were excluded. The sequential neurologic status was recorded. Tumor-associated spinal pain was prospectively scored according to the visual analogue scale (VAS).

Of 102 individuals, 22 (21.6%) died due to progression of their systemic disease. Mean survival after CKRS was 1.4 years (CI: 1.2-1.6). Karnofsky performance score was the only independent predictor of survival after radiosurgery on log-rank test (P < 0.0001), and on Cox regression analysis (hazard ratio, 0.864, P < 0.0001, CI: 0.809-0.922). Median survival after initial tumor diagnosis was 18.4 years (CI: 15.1-23.4). Two (2%) patients suffered complications after radiosurgery; a tumor hemorrhage occurred in one, and another developed spinal instability. These and 2 other patients were stabilized by kyphoplasty. Neurotoxicity or myelopathy was not observed. Local tumor control 15 months after CKRS was 98% (95% CI: 89-99%). Tumor-associated pain was observed in 52 (51%) patients. In these patients the median pretreatment pain score of VAS = 7 (95% CI: 6-7) was significantly reduced to VAS = 1 (95% CI: 4-6) (P < 0.001) within 1 week after CKRS. Analysis of variance identified the initial pain score as the only significant variable to predict pain reduction after CKRS (P < 0.03). Pain recurrence in correlation with tumor recurrence was observed for 3 (6%) patients.

Spinal radiosurgery with the CyberKnife technology is a nonivasive, safe, and effective treatment method for patients with 1 or 2 small spinal malignant tumors. The best benefit of the treatment can be expected in patients with good to excellent clinical condition and patients with severe tumor associated pain.