How can we consider variable RBE and LETd prediction during clinical practice? A pediatric case report at the Normandy Proton Therapy Centre using an independent dose engine

Abstract

Background To develop an auxiliary GPU-accelerated proton therapy (PT) dose and LETd engine for the IBA Proteus®ONE PT system. A pediatric low-grade glioma case study is reported using FRoG during clinical practice, highlighting potential treatment planning insights using variable RBE dose (DvRBE) and LETd as indicators for clinical decision making in PT. Methods The physics engine for FRoG has been modified for compatibility with Proteus®ONE PT centers. Subsequently, FRoG was installed and commissioned at NPTC. Dosimetric validation was performed against measurements and the clinical TPS, RayStation (RS-MC). A head patient cohort previously treated at NPTC was collected and FRoG forward calculations were compared against RS-MC for evaluation of 3D-Γ analysis and dose volume histogram (DVH) results. Currently, treatment design at NPTC is supported with fast variable RBE and LETd calculation and is reported in a representative case for pediatric low-grade glioma. Results Simple dosimetric tests against measurements of iso-energy layers and spread-out Bragg Peaks in water verified accuracy of FRoG and RS-MC. Among the patient cohort, average 3D-Γ applying 2%/2 mm, 3%/1.5 mm and 5%/1 mm were > 97%. DVH metrics for targets and OARs between FRoG and RayStation were in good agreement, with ∆D50,CTV and ∆D2,OAR both ⪅1%. The pediatric case report demonstrated implications of different beam arrangements on DvRBE and LETd distributions. From initial planning in RayStation sharing identical optimization constraints, FRoG analysis led to plan selection of the most conservative approach, i.e., minimized DvRBE,max and LETd,max in OARs, to avoid optical system toxicity effects (i.e., vision loss). Conclusion An auxiliary dose calculation system was successfully integrated into the clinical workflow at a Proteus®ONE IBA facility, in excellent agreement with measurements and RS-MC. FRoG may lead to further insight on DvRBE and LETd implications to help clinical decision making, better understand unexpected toxicities and establish novel clinical procedures with metrics currently absent from the standard clinical TPS.

Influence of beam pruning techniques on LET and RBE in proton arc therapy

“…This variation, coupled with the uncertainty of the model input parameters, leads to a reluctance of using variable RBE models in a clinical setting (52). An intermediate stage before clinical implementation of these models is an LET d and RBE evaluation approach, as demonstrated in this study, as well as previous literature (34,51,53,54). This means that clinical plans are optimized with respect to an RBE of 1.1, but other parameters are changed to improve the RBE-weighted dose and LET d distributions.…”

Spot‐scanning hadron arc (SHArc) therapy: A proof of concept using single‐ and multi‐ion strategies with helium, carbon, oxygen, and neon ions

“…Treatment plan design, optimization, and calculation took place with PRECISE (PaRticle thErapy using single and Combined Ion optimization StratEgies) TPS, 19 a novel particle therapy planning system previously established by coupling FRoG with the base code of an external optimizer previously developed 29,34,35 . FRoG has been extensively validated 36 and applied at multiple facilities as an auxiliary dose engine for particle therapy 22,37 . In this work, FRoG/PRECISE TPS were extended to enable calculation and optimization of SHArc treatments, using single‐ and multi‐ion strategies, involving different particle species (He, C, O, or Ne) as well as combinations of higher and lower LET ion beams (O+He or Ne+He).…”

“…29,34,35 FRoG has been extensively validated 36 and applied at multiple facilities as an auxiliary dose engine for particle therapy. 22,37 In this work, FRoG/PRECISE TPS were extended to enable calculation and optimization of SHArc treatments, using single-and multi-ion strategies, involving different particle species (He, C, O, or Ne) as well as combinations of higher and lower LET ion beams (O+He or Ne+He).…”