Session Item

Re-irradiation (reRT) of intracranial meningiomas is often difficult due to the limited radiation tolerance of the surrounding tissue and the risk of side effects. Aim of this analysis is to report outcomes, toxicities and prognostic factors of reRT in a large cohort of patients with recurrent meningiomas (RM) treated with different RT modalities.

We collected a multi-institutional database of meningioma patients who recurred after prior radiation therapy and underwent reRT with different modalities: radiosurgery (SRS), multi-fraction stereotactic radiotherapy (f-SRT), proton therapy (PT), Intensity-Modulated radiotherapy (IMRT) and External Beam radiotherapy (EBRT). Biologically Equivalent Doses in 2 Gy-fractions (EQD2) for normal tissue and tumor were estimated for each RT course (a/b =2 for brain tissue and a/b = 4 for meningioma), as well as Biological Effective Dose (BED). The primary outcome measure was progression-free survival (PFS). Secondary outcomes included overall survival (OS) and treatment-related toxicity. Toxicity was assessed according to Common Terminology Criteria for Adverse Events version 5.0 (CTCAE v5.0). Kaplan–Meier curves were generated to examine the effect of several parameters on PFS and on OS; Cox regression models were used to determine predictors of PFS and OS.

Between 2003 and 2021, 181 patients (pts) were included. Patients were re-irradiated with SRS (n = 75; 41.4%), f-SRT (n = 63; 34.8%), PT (n = 31; 17.1%) and conventional radiotherapy (n = 12; 6.7%). 78 pts were identified with WHO Grade I disease, 65 pts had Grade II disease, and 10 pts had Grade III disease. 28 pts who had no histologic sampling were grouped with Grade I patients for further analysis. Median age at re-irradiation was 62 (range, 20-89) and median KPS was 90 (range, 60-100). After a median follow-up of 4.6 years (interquartile range 1.7-6.8), 3-year PFS was 51.6% and 3-year OS 72.5%. At UVA Ki67 >5% (HR 2.81, 95% CI 1.48-5.34, p=0.002) and WHO grade > I (HR 3.08, 95% CI 1.80-5.28, p< 0.001) were negatively correlated with PFS, whereas f-SRT (HR 0.32, 95% CI 0.19-0.55, p<0.001), longer time to reRT (HR 0.37, 95% CI 0.21-0.67, p=0.001) and higher tumor BED (HR 0.45 95% CI 0.27-0.76, p=0.003) were positively correlated with PFS. At multivariate Cox analysis only f-SRT, time to reRT and tumor BED maintained their statistically significant prognostic impact on PFS (HR 0.36, 95% CI 0.21-0.64, p<0.001; HR 0.38, 95% CI 0.20-0.72, p=0.003 and HR 0.47 95% CI 0.26-0.83, p=0.01, respectively, Fig.1). Concerning toxicity, larger tumor GTV had a statistically significant higher risk of acute and late toxicity (p=.0.004 and p=0.005 respectively, Fig. 2).

Reirradiation of RM progressing after previous RT appears to be feasible with promising clinical outcomes and an acceptable toxicity profile. Prognostic factors in the decision-making process have been identified and should be incorporated in daily practice