Are Patients With Oligodendroglioma At Higher Risk For Radiation Neurotoxicity?

2061 Background: Symptomatic radiation neurotoxicity (RN), manifesting on MRI as focal necrosis and/or T2 signal abnormality, is a dreaded complication of radiation therapy (RT). While RT is standard of care for anaplastic gliomas, the long-term benefit vs risk profile in low-grade gliomas is not well defined. Patients with oligodendroglioma carry a better overall survival than those with astrocytoma. Anecdotally, they are more prone to experience RN than astrocytomas, as suggested by Acharya et al in 2017. We hypothesized that, independent of grade, oligodendrogliomas have a higher incidence of RN as compared to astrocytomas. Methods: We reviewed the records of 628 patients with WHO grade II and III gliomas from our institution. Study population comprised 326 patients with: standard fractionated RT, pathology confirmation by a neuropathologist, and follow up of at least 2 years after diagnosis. RN was defined as either histologically confirmed by pathology or requiring intervention for clinically presumed RN (bevacizumab or high-dose steroids.) A separate category included patients with dramatic cognitive decline with increased T2 signal abnormality, in the absence or tumor progression. Results: There were 131 patients with oligodendroglioma, based upon 1p/19q co-deletion (105 cases) or histology in the absence of molecular testing (26 cases). The remaining 195 patients had astrocytoma with intact 1p/19q, isocitrate dehydrogenase (IDH) wild-type, or diagnosed histologically absent molecular testing. The incidence of RN were 18.3% and 8.2% for oligodendroglioma and astrocytoma, respectively (p = 0.0063). An additional four patients with oligodendroglioma and two with astrocytoma had significant cognitive deterioration with increased T2 signal abnormality, without tumor progression. Conclusions: The greater than two-fold increase in RN incidence for oligodendrogliomas is significant and suggests patients with oligodendrogliomas may be more at risk to develop RN. Therefore, in patients with oligodendroglioma, the consideration of fractionated RT needs to be weighed against the increased potential for RN. Analysis of baseline imaging and patient characteristics variables that correlate with development of RN are ongoing and will be presented at the meeting.