Periventricular radionecrosis after conventionally fractionated radiation for low grade meningiomas

Radionecrosis (RN) is a serious late complication of radiotherapy (RT). While its risk is well characterized after stereotactic radiosurgery, RT dose thresholds for development of RN following conventionally fractionated RT (CFRT) are poorly defined; in the periventricular region, the risk of RN has not been systematically investigated. Our study objectives are therefore to estimate the incidence of periventricular white matter radionecrosis (PVRN) following CFRT for low grade meningiomas and identify associated clinical and dosimetric predictors. We chose a cohort of low-grade meningiomas (World Health Organization grade I–II) for this purpose because of their low recurrence risk, thus minimizing diagnostic uncertainty between RN and progression. This is a single-institution retrospective analysis of 135 adult patients who received CFRT between June 2011 and March 2023. The periventricular white matter was retrospectively contoured and dosimetric details to this region were extracted. PVRN was radiographically diagnosed and graded using Common Terminology Criteria for Adverse Events (CTCAE v5.0). Univariate analysis was performed to assess associations between PVRN and clinical or dosimetric variables. Logistic regression using restricted cubic splines and segmented models was used to identify dosimetric constraints predictive of PVRN. Median RT dose was 59.4 Gy (Gy) in 33 fractions; median follow-up was 66.5 months (range 1-151 months). 15% (n = 20) developed RN, with 11% (n = 15) PVRN and 6% (n = 8) grade 2 + PVRN. Overlap between the planning target volume and periventricular structures, as well as multiple high-dose constraints, were significantly associated with PVRN. V55 Gy to the periventricular substructure was the strongest predictor for both any-grade and grade 2 + PVRN; between 0 and 8 cc, V55 Gy values of 2.7, 3.6, and 4.8 cc were associated with < 5%, < 10%, and < 20% risk of grade 2 + PVRN, respectively. After excluding patients with prior cranial RT, V55 Gy remained the most predictive constraint with cutoff values of 2.7 and 3.1 cc associated with < 5% and < 10% risk of grade 2 + PVRN. Overlap with the periventricular region is associated with risk of symptomatic RN among patients receiving conventionally fractionated radiotherapy.