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Top Line: High-risk meningioma is an uncommon, but aggressive entity.
The Study: What is high-risk meningioma, anyway? Well, it’s not exactly the same as high grade meningioma. RTOG 0539 was a phase 2, risk-adaptive trial looking at the safety and efficacy of different treatment regimens for different risk levels of meningioma. "High-risk" was defined as any WHO grade III or any recurrent or new but sub-totally resected WHO grade II meningioma, and just over half of the patients had WHO II meningioma, most of which were recurrent. There were two clinical target volumes: a 2 cm expansion on gross tumor that received 1.8 Gy x 30 =54 Gy and a simultaneous integrated boost to a 1 cm expansion on gross tumor that received 2 Gy x 30 = 60 Gy. An important treatment planning note is that 40% of the plans required use of a modified planning target volume (typically another 3-5 mm margin) that received less than prescribed dose due to overlap with the planning reference volume of an adjacent critical organ (usually the optics). The primary outcome of 3-year progression free survival (PFS) was 59%. Interestingly, PFS for recurrent grade II tumors (45%) was worse than that for new grade III (65%). These findings suggest that observation of high risk meningioma—not uncommon, by the way—could lead to very poor outcomes and compromise subsequent treatment efficacy. Over 90% of all progression events occurred within the 54 Gy target volume and almost all of these were near or within the 60 Gy volume.
TBL: High-risk meningioma merits adjuvant radiation treatment, but we still have some detective work to do when it comes to optimizing treatment efficacy. | Rogers, Int J Radiat Oncol Biol Phys 2019