RADT-34. ANALYSIS OF A METHYLATION CLASS-GUIDED RADIOTHERAPY IN MENINGIOMA PATIENTS - AND THE PROSPECTIVE PHASE II MARCIE TRIAL WITH CARBON-ION BOOST RADIOTHERAPY

Abstract

Abstract Meningiomas represent the most common primary brain tumor type, with a recurrence rate of approximately 20% following resection. Classification by molecular classes was demonstrated to be more accurate in identifying patients at high risk of disease progression in meningiomas, compared to WHO grading only. Novel radiotherapeutic modalities using protons or carbon ions provide an increased relative biological effectiveness (RBE) compared to photons, enabling a higher local dose deposition while reducing the radiation dose for organs of risks. The prospective single-arm phase II - MARCIE trial investigated a bimodal radiotherapy using photons (50 Gy in 25 fractions) and a carbon-ions boost with 18 Gy (RBE) in 6 fractions. Local progression-free survival after 3 years was defined as primary endpoint. In total, 33 patients were recruited before termination of the trial. After 3 years, local progression free survival was estimated at 94.7% and overall survival at 89.8%. Serious adverse events in the form of radiation necrosis were observed in 3 cases, requiring a subsequent treatment with bevacizumab. Post-hoc DNA methylation profiling revealed that relapses occur more frequently in high-risk meningiomas following radiotherapy, compared to the intermediate risk-group, confirming the prognostic relevance of the methylation-based meningioma classifier.Subsequently, a retrospective matched-pair analysis was performed to compare irradiated (n > 100) and non-irradiated meningiomas, stratified into the molecular risk groups (ben, int, high). The clinical benefit of postoperative radiotherapy and dose escalation with regard to the local control are currently being assessed for the respective molecular meningioma classes. Postoperative, bimodal radiotherapy with carbon-ion boost represent an auspicious treatment modality with an excellent local tumor control following resection. Molecular risk stratification is crucial in identifying patients who might benefit from postoperative radiotherapy.