Association of 1p/19q Codeletion and Radiation Necrosis in Adult Cranial Gliomas After Proton or Photon Therapy

Purpose To analyze the incidence of and risk factors for clinically significant radiation necrosis (cRN) in adult cranial oligodendrogliomas and astrocytomas treated with proton or photon therapy. Methods and Materials Between 2007 and 2015, 160 patients with grade 2 or 3 oligodendrogliomas (with 1p/19q codeletion, n = 53) or astrocytomas (without 1p/19q codeletion, n = 107) were treated with proton (n = 37) or photon (n = 123) therapy. Clinically significant radiation necrosis (RN) was defined as symptomatic RN or asymptomatic RN that resulted in surgery or bevacizumab administration. The cumulative incidence was calculated using competing risks. Risk factors were identified using Cox proportional hazards. Results After a median follow-up period of 28.5 months, cRN developed in 18 patients (proton, 6; photon, 12). The 2-year cumulative incidence of cRN for proton and photon therapy was 18.7% (95% confidence interval [CI], 7.5%-33.8%) and 9.7% (95% CI, 5.1%-16%), respectively ( P  = .16). On multivariate analysis, risk factors for cRN included oligodendroglioma (hazard ratio [HR], 3.57; 95% CI, 1.38-9.25; P  = .009) and higher prescription dose (in gray relative biological equivalents [GyRBE]) (HR, 1.30; 95% CI, 1.05-1.61; P  = .015). The 2-year cumulative incidence of cRN in oligodendrogliomas and astrocytomas was 24.2% and 6.2%, respectively ( P  = .01). The relative volume (percentage) of brain receiving 60 GyRBE was a significant dosimetric predictor of cRN in oligodendrogliomas (HR, 1.11; 95% CI, 1.03-1.20; P  = .005). Conclusions The study showed that 1p/19q codeleted oligodendroglioma was a significant risk factor associated with cRN and the relative volume (percentage) of brain receiving 60 GyRBE was an important dosimetric predictor of cRN for oligodendroglioma patients. There is insufficient evidence at this time to conclude a significant difference in the incidence of cRN between proton and photon therapy.