084. Initial Experience Using Thermoplastic Mask-Based Immobilization for Stereotactic Radiosurgery in the Pediatric Patient

Authors: Matthew Jacob Recker, MD

Stereotactic radiosurgery (SRS) can be utilized in the treatment of neoplastic and vascular disease processes in the pediatric population. Precision is fundamental to safe and effective SRS and is traditionally accomplished by way of a stereotactic frame which is fixated to the skull. This methodology requires additional consideration and attention in pediatric patients. Thermoplastic mask immobilization employs a mounted cone-beam computed tomography system to define the stereotactic space and intrafraction motion detection system in lieu of a frame. This technology can obviate the need for frame based fixation in select patients.Methods: We queried our registry of radiosurgery cases since the installation of a thermoplastic mask compatible SRS system at our institution in February 2016. Patients under age 21 who underwent thermoplastic mask immobilization were included in our analysis.
6 patients (4 male) were included, one of whom underwent four treatments. One patient’s treatment was performed over 5 fractions, the remainder were treated in a single session, for a total of 13 treatment sessions. Mean age at day of treatment was 7.0 years (range 5.3-11.5). Sedation included general anesthesia (6), monitored anesthesia care (6), and none (1). A total of 21 lesions were targeted. Diagnoses included neuroblastoma metastatic to brain (2), atypical teratoid rhabdoid tumor (1), glioblastoma (1), medulloblastoma (1), and astrocytoma (1). Mean dose prescribed was 15.8 Gy (range 10-20). Mean volume of individual targets was 1.00 cm3. Mean prescribed treatment time was 39.95 minutes (range 13.3-87.99). Mean deviation from post stereotactic registration baseline was 0.15 mm which compares favorably with the 0.3 mm end to end accuracy expected from frame-based SRS in our setup. There were no periprocedural complications.
Thermoplastic mask-based immobilization provides an alternative to frame-based immobilization. Mask-based SRS may be a more favorable option in pediatric patients, especially for those who would benefit from a fractionated treatment.