Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Tokai, Japan.
Research Center for Nuclear Physics, Osaka University, Suita, Japan.
Int J Radiat Biol. 2021;97(10):1450-1460. doi: 10.1080/09553002.2021.1956003. Epub 2021 Jul 30.
The stochastic microdosimetric kinetic (SMK) model is one of the most sophisticated and precise models used in the estimation of the relative biological effectiveness of carbon-ion radiotherapy (CRT) and boron neutron capture therapy (BNCT). However, because of its complicated and time-consuming calculation procedures, it is nearly impractical to directly incorporate this model into a radiation treatment-planning system.
Through the introduction of Taylor expansion (TE) or fast Fourier transform (FFT), we developed two simplified SMK models and implemented them into the Particle and Heavy Ion Transport code System (PHITS). To verify the implementation, we calculated the photon isoeffective doses in a cylindrical phantom placed in the radiation fields of passive CRT and accelerator-based BNCT.
Our calculation suggested that both TE-based and FFT-based SMK models can reproduce the data obtained from the original SMK model very well for absorbed doses approximately below 5 Gy, whereas the TE-based SMK model overestimates the original data at higher doses. In terms of computational efficiency, the TE-based SMK model is much faster than the FFT-based SMK model.
This study enables the instantaneous calculation of the photo isoeffective dose for CRT and BNCT, considering their cellular-scale dose heterogeneities. Treatment-planning systems that use the improved PHITS as a dose-calculation engine are under development.
随机微观剂量动力学（SMK）模型是用于估计碳离子放射治疗（CRT）和硼中子俘获治疗（BNCT）的相对生物效应的最复杂和精确的模型之一。然而，由于其复杂且耗时的计算程序，几乎不可能直接将该模型纳入放射治疗计划系统。
通过引入泰勒展开（TE）或快速傅里叶变换（FFT），我们开发了两种简化的 SMK 模型，并将其实现到粒子和重离子传输代码系统（PHITS）中。为了验证实现，我们计算了放置在被动 CRT 和基于加速器的 BNCT 辐射场中的圆柱形体模中的光子等效应剂量。
我们的计算表明，基于 TE 的和基于 FFT 的 SMK 模型都可以很好地再现原始 SMK 模型获得的数据，大约在 5Gy 以下的吸收剂量，而基于 TE 的 SMK 模型在更高剂量下会高估原始数据。在计算效率方面，基于 TE 的 SMK 模型比基于 FFT 的 SMK 模型快得多。
本研究能够即时计算 CRT 和 BNCT 的光等效应剂量，考虑到它们细胞尺度的剂量不均匀性。正在开发使用改进的 PHITS 作为剂量计算引擎的治疗计划系统。
