The Risk of Radiation-induced Tumors or Malignant Transformation after Single-Fraction Intracranial Radiosurgery: Results Based on a 25-year Experience

Abstract Purpose To determine the risk of radiation-induced tumors or malignant transformation after single-fraction intracranial radiosurgery (SRS). Methods and Materials Retrospective review of 1,837 patients having single-fraction SRS for arteriovenous malformation (AVM) or benign tumor (meningioma, vestibular schwannoma, pituitary adenoma, glomus tumor) at a single center between 1990 and 2009. Patients were excluded if they refused research authorization (n=31), had a genetic predisposition for tumor development (n=84), had prior or concurrent radiation therapy (n=79), or had less than 5 years of imaging follow-up after SRS (n=501). The median imaging follow-up of the remaining 1,142 patients was 9.0 years (range, 5-24.9). Results No radiation-induced tumors were identified in 11,264 patient-years of follow-up after SRS. The risk of developing a radiation-induced tumor after SRS was 0.0% at 5-years (95% CI 0.0%-0.4%), 0.0% at 10-years (95% CI 0.0%-0.9%), and 0.0% at 15-years (95% CI 0.0%-2.8%). Seven of 316 meningioma patients (2.2%) and 1 of 358 vestibular schwannoma patients (0.3%) had malignant transformation at a median of 4.9 years (range, 2.8-13.8) after SRS. No cases of malignant transformation were noted in patients with pituitary adenomas (n=188) or glomus tumors (n=47). The 5-year, 10-year, and 15-year risk of malignant transformation was 0.5% (95% CI 0.0%-0.9%), 0.8% (95% CI 0.0%-1.8%), and 2.4% (95% CI 0.0%-5.5%), respectively. Patients having prior resection (HR=14.56, 95% CI 1.79-118.33, P=0.01) and meningioma pathology (HR=11.72, 95% CI 1.44-96.15, P=0.02) were at increased risk of malignant transformation. Conclusions The risk of radiation-induced tumors or malignant transformation after SRS is very low and should not be used as a justification for choosing alternative treatment approaches (surgical resection, observation) over SRS for appropriate patients.