Masuda Takamitsu, Kataoka Jun, Arimoto Makoto, Takabe Miho, Nishio Teiji, Matsushita Keiichiro, Miyake Tasuku, Yamamoto Seiichi, Inaniwa Taku, Toshito Toshiyuki
Graduate School of Advanced Science and Engineering, Waseda University, Tokyo, Japan.
Department of Medical Physics, Tokyo Women's Medical University, Tokyo, Japan.
Sci Rep. 2018 Feb 7;8(1):2570. doi: 10.1038/s41598-018-20906-z.
Monitoring the in vivo dose distribution in proton therapy is desirable for the accurate irradiation of a tumor. Although positron emission tomography (PET) is widely used for confirmation, the obtained distribution of positron emitters produced by the protons does not trace the dose distribution due to the different physical processes. To estimate the accurate dose from the PET image, the cross sections of nuclear reactions that produce positron emitters are important yet far from being sufficient. In this study, we measured the cross sections of O(p,x)O, O(p,x)N, and O(p,x)C with a wide-energy range (approximately 5-70 MeV) by observing the temporal evolution of the Cherenkov radiation emitted from positrons generated via β decay along the proton path. Furthermore, we implemented the new cross sectional data into a conventional Monte Carlo (MC) simulation, so that a direct comparison was possible with the PET measurement. We confirmed that our MC results showed good agreement with the experimental data, both in terms of the spatial distributions and temporal evolutions. Although this is the first attempt at using the Cherenkov radiation in the measurements of nuclear cross sections, the obtained results suggest the method is convenient and widely applicable for high precision proton therapy.
监测质子治疗中的体内剂量分布对于肿瘤的精确照射是很有必要的。尽管正电子发射断层扫描（PET）被广泛用于确认，但由于物理过程不同，质子产生的正电子发射体的分布并不能追踪剂量分布。为了从PET图像估计准确的剂量，产生正电子发射体的核反应截面很重要，但还远远不够。在本研究中，我们通过观察沿质子路径由β衰变产生的正电子发出的切伦科夫辐射的时间演化，测量了宽能量范围（约5 - 70 MeV）内的O(p,x)O、O(p,x)N和O(p,x)C的截面。此外，我们将新的截面数据应用于传统的蒙特卡罗（MC）模拟中，以便能够与PET测量进行直接比较。我们证实，我们的MC结果在空间分布和时间演化方面都与实验数据显示出良好的一致性。尽管这是首次尝试在核截面测量中使用切伦科夫辐射，但所获得的结果表明该方法方便且广泛适用于高精度质子治疗。
