Gray Laboratory, Department of Oncology, University of Oxford, Old Road Research Campus Research Building, Roosevelt Drive, Oxford OX3 7DQ, United Kingdom.
Green Templeton College, University of Oxford, 43 Woodstock Road, Oxford, OX2 6HG, United Kingdom.
Phys Med Biol. 2021 Feb 14;66(4):045028. doi: 10.1088/1361-6560/abddd0.
A practical neutron energy dependent RBE model has been developed, based on the relationship between a mono-energetic neutron energy and its likely recoil proton energy. Essentially, the linear energy transfer (LET) values of the most appropriate recoil proton energies are then used to modify the linear quadratic model radiosensitivities (α and β) from their reference LET radiation values to provide the RBE estimates. Experimental neutron studies published by Hall (including some mono-energetic beams ranging from 0.2 to 15 MeV), Broerse, Berry, and data from the Clatterbridge and Detroit clinical neutron beams, which all contain some data from a spectrum of neutron energies, are used to derive single effective neutron energies (NE) for each spectral beam. These energies yield a recoil proton spectrum, but with an effective mean proton energy (being around 50% of NE). The fractional increase in LET is given by the recoil proton LET divided by the proton (LET) value which provides the highest RBE. This ratio is then used to determine the change in the linear-quadratic model α and β parameters, from those of the reference radiation, to estimate the RBE. The predicted proton recoil RBE is then reasonably close to the experimental neutron RBE values found when taking into account the variation inherent in biological experiments. The work has some important consequences. The data of Hall et al (1975 Radiat. Res. 64 245-55) shows that the highest RBE values are found with neutron energies around 0.3-0.4 MeV, but this energy cannot possibly generate recoil proton energies which are higher, as necessary for a 0.68 MeV proton with a 30.5 keV μm LET (the LET value which provides the maximum obtainable RBE for a specified ion). For 0.4 MeV neutrons with proton recoil energies of around 0.2 MeV, the latter have a LET of around 62.88 keV μm. This could have an impact on proton beam RBE modelling. However, this is compensated by finding that the maximum radiosensitivity for mono-energetic neutrons was around 1.7 times larger than previously suggested from experimental ion beam studies, probably due to the necessary spreading out of Bragg peaks for ion beam experimental purposes, sampling errors and particle range considerations. This semi-empirical model can be used with minimal computer support and could have applications in ionic beams and in radioprotection.
已经开发出了一种实用的中子能量依赖性 RBE 模型，该模型基于单能中子能量与其可能的反冲质子能量之间的关系。从本质上讲，然后使用最合适的反冲质子能量的线性能量转移 (LET) 值来修改来自其参考 LET 辐射值的线性二次模型放射敏感性 (α 和 β)，以提供 RBE 估计。霍尔 (包括来自 0.2 到 15 MeV 的一些单能束)、Broerse、Berry 发表的实验性中子研究以及来自 Clatterbridge 和底特律临床中子束的数据，这些数据都包含了来自一系列中子能量的数据，用于为每个光谱束衍生单个有效中子能量 (NE)。这些能量产生反冲质子谱，但具有有效平均质子能量 (约为 NE 的 50%)。LET 的分数增加由反冲质子 LET 除以提供最高 RBE 的质子 (LET) 值给出。然后，使用该比值来确定从参考辐射的线性二次模型 α 和 β 参数的变化，以估计 RBE。考虑到生物学实验固有的变化，预测的质子反冲 RBE 与实验性中子 RBE 值非常接近。这项工作具有一些重要的意义。霍尔等人的数据 (1975 年 Radiat. Res. 64 245-55) 表明，最高的 RBE 值是在中子能量约为 0.3-0.4 MeV 时发现的，但这种能量不可能产生更高的反冲质子能量，因为对于具有 30.5 keV μm LET 的 0.68 MeV 质子 (对于指定离子可获得的最大 RBE 提供 LET 值) 需要更高的能量。对于质子反冲能量约为 0.2 MeV 的 0.4 MeV 中子，后者的 LET 约为 62.88 keV μm。这可能会对质子束 RBE 建模产生影响。然而，通过发现单能中子的最大放射敏感性大约是之前从实验性离子束研究中提出的 1.7 倍来弥补了这一点，这可能是由于离子束实验目的、采样误差和粒子射程考虑因素导致的布拉格峰的必要扩散。这种半经验模型可以在最小的计算机支持下使用，并可能在离子束和放射防护中得到应用。
