Presentation A simulation study on detection of a cavity across a therapeutic carbon beam using secondaty electron bremsstrahlung

山口, 充孝  ,  長尾, 悠人  ,  佐藤, 隆博  ,  神谷, 富裕  ,  酒井, 真理  ,  菅井, 裕之  ,  荒川, 和夫  ,  河地, 有木

The purpose of this work was to study the feasibility of detection of a cavity across a therapeutic C-12 beam in a phantom by measuring low-energy (63-68 keV) secondary electron bremsstrahlung (SEB) emitted from a beam trajectory. Monte Carlo simulations were performed using the Particle and Heavy Ion Transport code System (PHITS). A C-12 beam (290 MeV/u) was injected on an acrylic target having an air cavity across the beam axis. To measure the depth dependence of the SEB intensity, a gamma camera consisting of a lead collimator having thirty-nine slits and a cadmium-telluride detector having thirty-nine elements was placed around the target. Both the slits and detector elements were arrayed along the beam axis and the position of the center of each slit was set to that of each detector element. Distributions of energy depositions in the detector elements were recorded. In addition, the distribution without SEB generation was calculated by performing a simulation again. These two simulations were repeated with the same setup other than without the cavity. We found that the yields having energy deposition of 63–68 keV with both the SEB generation and the air cavity have a valley in the cavity region, in contrast no valley appeared in the result without the cavity. The yields without SEB generation reached 40–50% of that with SEB generation and had no valleys. These results indicate that the SEB component can be utilized for monitoring of air cavities.

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