生物・医学用52MeV陽子線照射コースの整備と吸収線量評価

概要

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A 52MeV proton irradiation course for biological and medical use was consolidated at the FM cyclotron of the Institute for Nuclear Study, University of Tokyo. The course was equipped with a 0.2mm thick stainless steel beam scatterer, an absorbed dose monitoring ionization chamber, a rotating 2-dimensional beam profile monitor, a range modulator and a Faraday cup. Absorbed dose was measured with a parallel-plate tissue-equivalent chamber and the Faraday cup, and both measurements agreed each other within a 7.5% error. The beam flatness was greatly improved by the 0.2mm thick stainless steel beam scatterer installed in about 5m upstream from the irradiation point, and the reproducibility of the depth-dose distribution was also improved. However, since there is no beam analyzing apparatus between the cyclotron and, the irradiation point, the beam profile stability was not good enough and the beam shaping by the collimator was not sharp. The effect of multiple scattering at the range modulator placed in 26cm upstream from the irradiation point was noticeable, but it was well evaluated by some simple theoretical formulae.