Effectiveness of Intensity Modulate Proton Therapy in Managing Complex Multiple Meningiomas: A Dosimetric and...

This study addresses the challenges of sparing neurological organs at risk (OARs) in radiation therapy for multiple meningiomas (MM) by introducing a novel, robust intensity-modulated proton therapy (IMPT) plan and assessing its dosimetric and radiobiological outcomes relative to helical tomotherapy (HT).

CT and MRI datasets from 24 MM patients were used to generate competing IMPT and HT plans. IMPT employed a spot-assignment strategy with five static fields and was robustly optimized for CTV-sum, considering 2-3 mm setup and 2% range uncertainty, while HT was optimized on PTV-sum. The median prescribed dose was 50.2 GyRBE in 28 fractions.

The number of isolated CTVs per patient ranged from 2 to 9, with total target volumes of 27.69-1153.61 cc (CTV-sum) and 62.5-1415.25 cc (PTV-sum). The mean±SD dose difference in D_95% between PTV-sum in HT and CTV-sum in the IMPT worst-case scenario (-0.58 ± 0.57 GyRBE, p = 0.03) was clinically acceptable. While D_mean to PTV-sum showed no significant difference (p = 0.06), D2% was significantly higher in IMPT (p = 0.006) than in HT. IMPT significantly reduced both D_max and D_mean for most OARs (p < 0.05) and lowered integral dose to normal brain tissue (p < 0.0001) by a factor of 1.37-6.97 compared to HT. Significant NTCP reductions (p < 0.05) were observed for the lenses, eyes, brainstem, optic nerves, and cochlea.

IMPT ensures robust target coverage while significantly lowering D_max, D_mean, and NTCP for several OARs compared to HT. Its reduced integral dose to normal brain tissue may benefit re-irradiation and lower second cancer risk.