ESTRO 2023 - Abstract Book

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ESTRO 2023

this study, we present both data from cell experiments trying to reproduce the biological effect and a Monte Carlo study on the reaction probability of both the p+11B and n+10B reaction channel, since both isotopes are present in the BSH in [1]. Materials and Methods Cell culture flasks were placed in a water tank in the middle of the SOBP. Cultures of the V79 cell line were irradiated with a 9x9 cm ² uniform field, with the SOBP ranging from 6-9 cm. Cell survival curves were produced at 6 dose points ranging from 1-10 Gy with 6 control flasks. Each dose point consisted of 3 biological replicates, either with or without BSH enriched (0.17 µ g/ml) medium. Furthermore, we simulated the same proton field, irradiating a water phantom using TOPAS and SHIELD-HIT12A Monte Carlo particle transport codes. Cell culture flask was positioned in the simulated water tank containing medium with natural boron. We calculated the yield of different boron nuclear reactions, fluence of relevant particles and how they change depending on the geometry of the simulated setup and choice of physics software. Results No statistical significance between the regular and BSH exposed cells was observed in the survival curves, fig. 1. However, an apparent BSH toxicity affected the colony growth and plating efficiency. The BSH component was analyzed and significant amounts of the toxic BSSH dimer was present, even though the compound was stored in protective gas. A photon (6 MV linac) reference experiment further indicated BSH toxicity, but no radiosensitization. MC simulations show the n+10B capture reaction produces a factor of 177 +/-24 more high-LET particles than the originally proposed p+11B reaction. By varying the phantom (fig. 2) and field it was found that the fluence of low energy neutrons needed for the 10B reaction can increase/decrease up to two orders of magnitude. The conflicting results in published work prior to this study could attribute to the fact that too small phantom and field s were simulated which resulted in an underestimation of low energy neutron fluence in the proton beam of 1-3 orders of magnitude.

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