Center of Molecular Imaging, Radiotherapy and Oncology, Insitut de recherche expérimentale et clinique, Université catholique de Louvain, Brussels, Belgium.
Phys Med Biol. 2013 Aug 21;58(16):5363-80. doi: 10.1088/0031-9155/58/16/5363. Epub 2013 Jul 23.
Based on experiments and numerical simulations, a study is carried out pertaining to the conversion of dose-to-graphite to dose-to-water in a carbon ion beam. This conversion is needed to establish graphite calorimeters as primary standards of absorbed dose in these beams. It is governed by the water-to-graphite mass collision stopping power ratio and fluence correction factors, which depend on the particle fluence distributions in each of the two media. The paper focuses on the experimental and numerical determination of this fluence correction factor for an 80 MeV/A carbon ion beam. Measurements have been performed in the nuclear physics laboratory INFN-LNS in Catania (Sicily, Italy). The numerical simulations have been made with a Geant4 Monte Carlo code through the GATE simulation platform. The experimental data are in good agreement with the simulated results for the fluence correction factors and are found to be close to unity. The experimental values increase with depth reaching 1.010 before the Bragg peak region. They have been determined with an uncertainty of 0.25%. Different numerical results are obtained depending on the level of approximation made in calculating the fluence correction factors. When considering carbon ions only, the difference between measured and calculated values is maximal just before the Bragg peak, but its value is less than 1.005. The numerical value is close to unity at the surface and increases to 1.005 near the Bragg peak. When the fluence of all charged particles is considered, the fluence correction factors are lower than unity at the surface and increase with depth up to 1.025 before the Bragg peak. Besides carbon ions, secondary particles created due to nuclear interactions have to be included in the analysis: boron ions ((10)B and (11)B), beryllium ions ((7)Be), alpha particles and protons. At the conclusion of this work, we have the conversion of dose-to-graphite to dose-to-water to apply to the response of a graphite calorimeter in an 80 MeV/A carbon ion beam. This conversion consists of the product of two contributions: the water-to-graphite electronic mass collision stopping power ratio, which is equal to 1.115, and the fluence correction factor which varies linearly with depth, as k(fl, all) = 0.9995 + 0.0048(zw-eq). The latter has been determined on the basis of experiments and numerical simulations.
基于实验和数值模拟，对碳离子束中从石墨剂量转换为水剂量的问题进行了研究。为了在这些束中建立石墨量热计作为吸收剂量的主要标准，需要进行这种转换。它由水-石墨质量碰撞阻止本领比和通量修正因子决定，而这些因子取决于两种介质中的粒子通量分布。本文重点介绍了用于 80 MeV/A 碳离子束的这种通量修正因子的实验和数值确定。测量是在意大利西西里岛卡塔尼亚的 INFN-LNS 核物理实验室进行的。数值模拟是通过 GATE 模拟平台使用 Geant4 蒙特卡罗代码进行的。实验数据与通量修正因子的模拟结果非常吻合，并且接近 1.010。在布拉格峰区域之前，实验值随深度增加而增加。它们的不确定度为 0.25%。根据计算通量修正因子时采用的近似程度，会得到不同的数值结果。仅考虑碳离子时，在布拉格峰之前，测量值与计算值之间的差异最大，但值小于 1.005。在表面处数值接近 1.005，并在布拉格峰附近增加到 1.005。当考虑所有带电粒子的通量时，在表面处通量修正因子小于 1.005，并随深度增加到布拉格峰前的 1.025。除了碳离子之外，由于核相互作用而产生的次级粒子也必须包括在分析中：硼离子（(10)B 和 (11)B）、铍离子((7)Be）、α粒子和质子。在这项工作的结论中，我们将石墨剂量转换为水剂量应用于 80 MeV/A 碳离子束中石墨量热计的响应。这种转换由两个贡献的乘积组成：水-石墨电子质量碰撞阻止本领比，等于 1.115，以及随深度线性变化的通量修正因子，即 k(fl, all) = 0.9995 + 0.0048(zw-eq)。后者是基于实验和数值模拟确定的。
