会議発表用資料 Monte Carlo study on the feasibility of mini-beam radiation therapy with ion beams

Matsufuji, Naruhiro

2017-10-16
内容記述
Elevating energy loss of swift ion beams traveling in a matter toward their range end, known as Bragg peak, makes cancer therapy with the ion beams (ion-beam RT) advantageous over conventional X-ray. The localized dose delivery to the Bragg peak enables to control deep-seated tumor cells while sparing surrounding benign tissues. The Bragg peak gets shaper for heavier ions; additionally, the biological effectiveness of carbon and its vicinity also increases gradually in accordance with increasing energy loss. Idea of the mini-beam radiation therapy (MBRT) was initially studied with X-ray as a method to spare proximal normal tissues by irradiating through submillimeter slit collimator. Recent studies try to apply the MBRT concept for proton beam by interlacing multiple sparse heterogeneous fields. The combination of the MBRT with ion-beam RT may lead further reduction of normal tissue toxicities and/or add new aspect for the selection of ion species for cancer therapy. In considering the MBRT with ion beams, it is requisite to precisely evaluate the spatial distribution of each mini beam travelling in a matter. This study aims at demonstrating the efficacy of the ion-beam MBRT for various ion species with Monte-Carlo (MC) transport simulation of the therapeutic ion beams. A MC code PHITS was used to simulate the spatial dose distribution in water for ion species between proton and neon. Incident energy was selected to reach 15 cm depth in water. As a figure of merit, a peak-to-valley ratio (PVR) by the adjacent mini beams was evaluated at various irradiation depths under the parallel opposing field configuration. The result showed that PVR at the plateau region could be maximized in case of proton beam. The multiple scattering of the proton beam became significant especially around the range end. It enabled in turn to keep plenty of distance of adjacent beams. For heavier ion species, even though the multiple scattering of the primary beam was suppressed, dose reduction at valley by MBRT was found still possible due to the spatial distribution of fragment particles originated from projectile ions. The simulation result with FLUKA is also shown for the sake of comparison.
International conference on Monte Carlo techniques for medical applications (MCMA2017)

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