CyberKnife Radiosurgery for the Management of Skull Base and Spinal Chondrosarcomas

The use of CyberKnife (CK) stereotactic radiosurgery (SRS) for the management of central nervous system chondrosarcomas has not been previously reported. To evaluate outcomes of primary, recurrent, and metastatic chondrosarcomas of the skull base and spine treated with CK SRS, a retrospective observational study of 16 patients treated between 1996 and 2011 with CK SRS was performed using an IRB-approved database at Stanford University Medical Center. Twenty lesions (12 cranial, 8 spinal) across six males and ten females were analyzed. The median age at SRS was 51 years and median follow-up was 33 months. Median tumor volume was 11.0 cm³ and median marginal dosages were 22, 24, 26, 27, and 30 Gy for one to five fractionations, respectively. Overall Kaplan-Meier survival rates were 88, 88, 80, and 66 % at 1, 3, 5, and 10 years after initial presentation. Survival rates at 1, 3, and 5 years after CK were 81, 67, and 55 %, respectively. Actuarial tumor control was 41 ± 13 % at 60 months. At 36 months follow-up, tumor control was 80 % in primary lesions, 50 % in recurrent lesions, and 0.0 % in metastatic disease (p = 0.07). Tumor control was 58 % in cranial lesions and 38 % in spinal lesions. Radiation injury was reported in one patient. CK SRS appears to be a safe adjuvant therapy and offers moderate control for primary cranial chondrosarcoma lesions. There appears to be a clinically, albeit not statistically, significant trend towards poorer outcomes in similarly treated metastatic, recurrent, and spinal chondrosarcomas (p = 0.07). Lesions not candidates for single fraction SRS may be treated with hypofractionated SRS without increased risk for radiation necrosis.