P128] Spatial fractionation of the dose in charged particle therapy: Dosimetry evaluations

Abstract

Introduction The dose of tolerance of normal tissues continues being the main limitation in radiotherapy. To overcome it, we propose to ally the inherent physical advantages of charged particle therapy with the normal tissue preservation observed when irradiated with submillimetric spatially fractionated beams (minibeam radiation therapy, MBRT) [1] , [2] . This would allow the use of higher and potentially curative doses in the treatment of radioresistant tumors. Materials and methods A dosimetry evaluation was performed by means of Monte Carlo simulations (GATE/Geant4). Relevant dosimetric parameters such the peak-to-valley dose ratios (PVDR) were assessed. Special attention was given to the contribution of nuclear fragmentation to the valley doses, considered the main responsible of tissue sparing. The optimum irradiation configuration in heavy ion spatially fractionated radiotherapy in terms of ion species, beam width, center-to-center distances (ctc), and linear energy transfer (LET) was assessed. Results Our results show that beam widths larger than 400 μ m are needed to keep a ratio between the dose in the entrance and the dose in the target of the same order as in conventional irradiations. A large ctc distance (3500 μ m) would favor tissue sparing since it provides higher PVDR, it leads to a reduced contribution of the heavier nuclear fragments and a LET value in the valleys a factor lower than ctc leading to homogenous distributions in the target. Among the di?erent ions species evaluated, Ne stands as the one leading to the best balance between high peak-to-valley dose ratio and peak-to-valley-LET ratio in normal tissues and high LET values (close to 100 keV/ μ m) in the target region. Conclusions The dosimetric data obtained supports the exploration of this radiotherapy approach. Although biological experiments are warranted to confirm the therapeutic gain, the results of this work may be used to guide the future biological studies.