Hasselt University, Faculty of Engineering Technology - Nuclear Technology (NuTeC), Hasselt, Belgium.
KU Leuven, department of Oncology, Leuven, Belgium.
Phys Med Biol. 2023 Oct 31;68(21). doi: 10.1088/1361-6560/ad03a9.
This study evaluates a compact Monte Carlo (MC) model of a pencil beam scanning clinical proton beam using TOPAS to estimate the dose out-of-field (OOF). Compact modelling means that the model starts from a pristine proton beam at the nozzle exit, customised based on acceptance and commissioning data, instead of modelling the full treatment head and room.: First, in-field validation tests were performed. Then, the OOF dose was validated in an RW3 phantom with bubble detectors for personal neutron dosimetry (measuring the neutron dose equivalent) and thermoluminiescent detectors (measuring the absorbed dose by protons and gammas). Measurements were performed at 15 and 35 cm from the distal edge of the field for five different irradiation plans, covering different beam orientations, proton energies and a 40 mm range shifter. TOPAS simulations were performed with QGSP Binary Cascade HP (BIC) and QGSP Bertini HP (Bertini) hadron physics lists.: In-field validation shows that MC simulations agree with point dose measurements within -2.5 % and +1.5 % at locations on- and off-axis and before, in and after the Bragg peak or plateau. The gamma passing rate 2%/3mm of four simulated treatment plans compared to the dose distribution calculated by the TPS exceeds 97 % agreement score. OOF dose simulations showed an average overestimation of 27 % of the neutron dose equivalent for the BIC hadron physics list and an average underestimation of 20 % for the Bertini hadron physics list. The simulated absorbed dose of protons and gammas showed a systematic underestimation which was on average 21 % and 51 % for BIC and Bertini respectively.: Our study demonstrates that a compact MC model can reliably produce in-field data, while out-of-field dose data are within the uncertainties of the detector systems and MC simulations nuclear models, and do so with shorter modelling and faster calculation time.
本研究使用 TOPAS 评估了一种紧凑的笔束扫描临床质子束蒙特卡罗（MC）模型，以估算场外剂量（OOF）。紧凑建模意味着该模型从喷嘴出口处的原始质子束开始，根据验收和调试数据进行定制，而不是对整个治疗头和治疗室进行建模。首先，进行了场内验证测试。然后，在 RW3 体模中使用泡室探测器进行个人中子剂量测量（测量中子剂量当量）和热释光探测器（测量质子和伽马吸收剂量）对 OOF 剂量进行了验证。在距离射野远端边缘 15 和 35 cm 处，对五个不同的照射计划进行了测量，这些计划涵盖了不同的束方向、质子能量和 40 mm 射程移动器。使用 QGSP Binary Cascade HP（BIC）和 QGSP Bertini HP（Bertini）强子物理列表进行了 TOPAS 模拟。场内验证表明，MC 模拟与点剂量测量值的符合度在轴上和轴外位置以及布拉格峰或平台之前、之中和之后分别在-2.5%和+1.5%范围内。与 TPS 计算的剂量分布相比，四个模拟治疗计划的 2%/3mm 伽马通过率超过 97%符合率。OOF 剂量模拟结果表明，BIC 强子物理列表的中子剂量当量平均高估了 27%，Bertini 强子物理列表的中子剂量当量平均低估了 20%。质子和伽马的模拟吸收剂量显示出系统低估，BIC 和 Bertini 的平均低估分别为 21%和 51%。本研究表明，紧凑的 MC 模型可以可靠地产生场内数据，而场外剂量数据在探测器系统和 MC 模拟核模型的不确定性范围内，并且具有更短的建模和更快的计算时间。
