Radiosurgery for benign tumors of the spine using the Synergy S with cone-beam computed tomography image guidance

Abstract

Object There is a growing body of evidence to support the safe and effective use of spine radiosurgery. However, there is much less experience regarding the use of radiosurgery for the treatment of benign as opposed to malignant spine tumors. This study represents an evaluation of, and reporting on, the technical aspects of using a dedicated radiosurgery system for the treatment of benign spine tumors. Methods Forty-five consecutive benign spine tumors were treated using the Elekta Synergy S 6-MV linear accelerator with a beam modulator and cone-beam computed tomography (CBCT) image guidance technology for target localization. The study cohort included 16 men and 29 women, ranging in age from 23 to 88 years (mean age 52 years). There were 14 cervical, 12 thoracic, 14 lumbar, and 5 sacral tumors. Forty-one lesions (91%) were intradural. The most common histological types of tumor were schwannoma, neurofibroma, and meningioma. Indications for radiosurgery included primary treatment in 24 cases (53%) and treatment of recurrent or residual tumor after open resection in 21 cases (47%). Results No subacute or long-term spinal cord or cauda equina toxicity occurred during the follow-up period (median 32 months). The mean maximum dose received by the gross tumor volume (GTV) was 16 Gy (range 12–24 Gy) delivered in a single fraction in 39 cases. The mean lowest dose received to the GTV was 12 Gy (range 8–16 Gy). The GTV ranged from 0.37 to 94.5 cm3 (mean 13.7 cm3, median 5.9 cm3). In the majority of cases, a planning target volume expansion of 2 mm was employed (38 cases; 84%). The mean maximum point dose delivered to the spinal cord was 8.7 Gy (range 4–11.5 Gy); the mean volume of the spinal cord that received greater than 8 Gy was 0.9 cm3 (range 0.0–5.1 cm3); and the mean dose delivered to 0.1 cm3 of the spinal cord was 7.5 Gy (range 3–10.5 Gy). The mean maximum point dose delivered to the cauda equina was 10 Gy (range 0–13 Gy); the mean volume of the cauda equina that received greater than 8 Gy was 1.45 cm3 (range 0.0–10.6 cm3); and the mean dose delivered to 0.1 cm3 of the cauda equina was 8 Gy (range 0.5–11 Gy). Conclusions In this study the authors describe the contouring and prescribed dose techniques used in the treatment planning and delivery of radiosurgery for benign neoplasms of the spine using CBCT image guidance. This technique may serve as an important reference for the performance of radiosurgery when one believes it is clinically indicated as a treatment modality for a benign spine tumor that is associated with both a high safety profile and a strong positive clinical outcome.