Graduate School of Biomedical Engineering, Tohoku University, Sendai, Japan.
Institute of Nuclear Medical Physics, AERE, Bangladesh Atomic Energy Commission, Dhaka, Bangladesh.
PLoS One. 2022 Feb 15;17(2):e0263521. doi: 10.1371/journal.pone.0263521. eCollection 2022.
The Monte Carlo method is employed in this study to simulate the proton irradiation of a water-gel phantom. Positron-emitting radionuclides such as 11C, 15O, and 13N are scored using the Particle and Heavy Ion Transport Code System Monte Carlo code package. Previously, it was reported that as a result of 16O(p,2p2n)13N nuclear reaction, whose threshold energy is relatively low (5.660 MeV), a 13N peak is formed near the actual Bragg peak. Considering the generated 13N peak, we obtain offset distance values between the 13N peak and the actual Bragg peak for various incident proton energies ranging from 45 to 250 MeV, with an energy interval of 5 MeV. The offset distances fluctuate between 1.0 and 2.0 mm. For example, the offset distances between the 13N peak and the Bragg peak are 2.0, 2.0, and 1.0 mm for incident proton energies of 80, 160, and 240 MeV, respectively. These slight fluctuations for different incident proton energies are due to the relatively stable energy-dependent cross-section data for the 16O(p,2p2n)13N nuclear reaction. Hence, we develop an open-source computer program that performs linear and non-linear interpolations of offset distance data against the incident proton energy, which further reduces the energy interval from 5 to 0.1 MeV. In addition, we perform spectral analysis to reconstruct the 13N Bragg peak, and the results are consistent with those predicted from Monte Carlo computations. Hence, the results are used to generate three-dimensional scatter plots of the 13N radionuclide distribution in the modeled phantom. The obtained results and the developed methodologies will facilitate future investigations into proton range monitoring for therapeutic applications.
本研究采用蒙特卡罗方法模拟质子辐照水凝胶体模。采用粒子和重离子传输代码系统蒙特卡罗代码包对放射性核素如 11C、15O 和 13N 的正电子发射进行评分。先前的研究报告表明，由于 16O(p,2p2n)13N 核反应的阈能相对较低（5.660 MeV），在实际布拉格峰附近形成了 13N 峰。考虑到生成的 13N 峰，我们获得了各种入射质子能量（45 至 250 MeV，能量间隔为 5 MeV）下 13N 峰与实际布拉格峰之间的偏移距离值。偏移距离在 1.0 至 2.0 mm 之间波动。例如，对于入射质子能量为 80、160 和 240 MeV 的情况，13N 峰与布拉格峰之间的偏移距离分别为 2.0、2.0 和 1.0 mm。对于不同的入射质子能量，这些微小的波动是由于 16O(p,2p2n)13N 核反应的能量相关截面数据相对稳定。因此，我们开发了一个开源计算机程序，可以对偏移距离数据与入射质子能量进行线性和非线性插值，进一步将能量间隔从 5 MeV 减小到 0.1 MeV。此外，我们还进行了光谱分析以重建 13N 布拉格峰，结果与蒙特卡罗计算预测的结果一致。因此，这些结果用于生成模型体模中 13N 放射性核素分布的三维散射图。所获得的结果和开发的方法将有助于未来对治疗应用中质子射程监测的研究。
