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Spatial fractionation of the dose in heavy ions therapy: An optimization study
Author(s) -
González W.,
Prezado Y.
Publication year - 2018
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12902
Subject(s) - linear energy transfer , oxygen enhancement ratio , dosimetry , ion , monte carlo method , materials science , particle therapy , irradiation , heavy ion , beam (structure) , relative biological effectiveness , ion beam , absorbed dose , nuclear medicine , physics , nuclear engineering , nuclear physics , optics , mathematics , statistics , medicine , quantum mechanics , engineering
Purpose The alliance of charged particle therapy and the spatial fractionation of the dose, as in minibeam or Grid therapy, is an innovative strategy to improve the therapeutic index in the treatment of radioresistant tumors. The aim of this work was to assess the optimum irradiation configuration in heavy ion spatially fractionated radiotherapy (SFRT) in terms of ion species, beam width, center‐to‐center distances, and linear energy transfer (LET), information that could be used to guide the design of the future biological experiments. The nuclear fragmentation leading to peak and valley regions composed of different secondary particles, creates the need for a more complete dosimetric description that the classical one in SFRT. Methods Monte Carlo simulations (GATE 6.2) were performed to evaluate the dose distributions for different ions, beam widths, and spacings. We have also assessed the 3D‐maps of dose‐averaged LET and proposed a new parameter, the peak‐to‐valley‐LET ratio, to offer a more thorough physical evaluation of the technique. Results Our results show that beam widths larger than 400 μ m are needed in order 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 2 lower than the LET in the ctc leading to homogeneous distributions in the target. Conclusions Heavy ions MBRT provide advantageous dose distributions. Thanks to the reduced lateral scattering, the use of submillimetric beams still allows to keep a ratio between the dose in the entrance and the dose in the target of the same order as in conventional irradiations. Large ctc distances (3500 μ m) should be preferred since they lead to valley doses composed of lighter nuclear fragments resulting in a much reduced dose‐averaged LET values in normal tissue, favoring its preservation. Among the different ions species evaluated, Ne stands out as the one leading to the best balance between high PVDR and PVLR in normal tissues and high LET values (close to 100 keV/ μ m) and a favorable oxygen enhancement ratio in the target region.