237 Stereotactic Radiotherapy to Spine and Non-Spine Bone Metastases in Nova Scotia

Purpose: There is increasing use of hypofractionated stereotactic radiosurgery (HSRS) for the treatment of intact brain metastases and surgical cavities.Unlike single fraction stereotactic radiosurgery (SRS), limited data exist quantifying the risk of radiation necrosis (RN) specific to HSRS.We present our analyses of the risk of RN following 5 daily fraction HSRS to surgical cavities and intact metastases and respective predictors.Materials and Methods: Eighty-seven consecutively treated patients with 118 surgical cavities and 132 intact metastases were retrospectively reviewed.All patients were treated with thermoplastic mask immobilization using a cone-beam CT (CBCT) image-guided linac with a multi-leaf collimator (MLC) and sixdegrees-of-freedom treatment couch.All patients were treated with 5 daily fractions with a 2mm planning target volume (PTV) applied.Clinical and dosimetric variables were assessed to identify predictors of RN including the total volume of the brain minus the CTV (BMC) receiving 5 to 30 Gy in 5Gy increments, where the CTV was the surgical cavity for resected lesions and equaled the GTV for intact lesions.