How can scanned proton beam treatment planning for low‐grade glioma cope with increased distal RBE and locally increased radiosensitivity for late MR‐detected brain lesions?

A novel risk model has recently been proposed for the occurrence of late contrast-enhancing brain lesions (CEBLs) after proton irradiation low-grade glioma (LGG) patients. It predicts a strong dependence on dose-weighted linear-energy transfer (LETd effect) and an increased radiosensitivity ventricular proximity, 4-mm fringe surrounding system (VP4mm effect). On this basis, we investigated (A) how these two factors patient-specific anatomical treatment plan (TP) features contribute to normal tissue complication probability (NTCP) (B) if conventional LETd-reduction techniques like multiple-field TP are able reduce NTCP. The LGG cohort (N = 110) was stratified with respect prescribed dose, tumor grade, field configuration. NTCP predictions CEBL rates per strata were analyzed. effect in patient groups: (i) nine high-risk subjects extended lateral target volumes who had developed CEBLs single-beam treatments retrospectively replanned clinical standard two-field setting using almost orthogonal fields strictly opposing fields, (ii) single-field simulated seven low-risk patients small central clinically treated fields. In cohort, identified exposure radiosensitive VP4mm components biological effectiveness as dominant driving factor. We observed that larger location main ventricles, both being characteristic WHO°II tumors, presented highest risks. Among equal dose prescription 54 Gy(RBE), median obtained group sharp angles. Regarding plans, found reduction only achievable where LETd dominates is small. plans 23% higher compared plan. group, risk, scenarios yielded 44% plans. interplay creates geometric complexity can hardly be managed by current TP. Our results underline advanced biologically guided approaches become crucial effective minimization therapy LGG.