FiR 1 epithermal neutron beam model and dose calculation for treatment planning in neutron capture therapy
FiR 1 epithermal neutron beam model and dose calculation for treatment planning in neutron capture therapy
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FiR 1 超热中子束模型和剂量计算，用于中子俘获治疗中的治疗计划
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发表时间：
2002
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通讯作者：
T. Seppälä
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作者：
T. Seppälä
芬兰硼中子俘获治疗（BNCT）设施（FiR 1）的超热中子束模型是使用二维（2D）离散纵坐标输运（DORT）代码创建的。利用DORT模型对束流进行了优化设计：计算了中子慢化剂的最佳厚度和束流铋准直器的长度和厚度。最终的束流模型进行了验证实验与剂量测量。计算出的中子束能谱首先用空气中的活化测量进行了验证。合适的脑组织替代中子俘获治疗（NCT）剂量测定进行了检查。计算的热中子注量[和金（Au）和锰（Mn）的活化反应率]，γ剂量和快中子剂量分布在三个组织替代（TS）phantomy验证与活化和对电离室测量。从DORT模型出发，建立了治疗计划系统（TPS）的中子-光子束简化模型。TPS光束模型在三个TS体模中进行了实验验证。将射束模型归一化为PMMA（聚甲基丙烯酸甲酯）体模中热中子最大值处的Au活化测量值，该体模可链接到监测器单元。TPS中的计划辐射剂量以监测单位给出。实验验证的束模型首先应用于狗脑的剂量计划的计算和在芬兰BNCT项目中的多形性胶质母细胞瘤（GBM）患者的治疗计划。FiR 1超热中子束的二维圆柱对称水平DORT模型是研究不同几何结构（慢化剂、准直器）对中子和光子谱影响的有效和可靠的工具。在简单的体模材料中，发现PMMA在准直超热中子束中比水更接近脑组织中最大热中子注量的3个百分比单位。然而，水模拟脑组织中的吸收伽马剂量比PMMA更接近12个百分比单位。此外，还设计了一种脑组织等效液。在水、PMMA和脑等效液体中的射束模型的平行验证证实了NCT剂量计算的可靠性。DORT射束模型足够准确（强度校正5%），可用作TPS中的射束模型。在PMMA体模中的热中子最大值处，用Au活化测量对射束模型进行归一化。使用计算的Au活化反应速率（变化3%）进行归一化，发现与计算的Mn活化反应速率（变化13%）相比，与截面的能量分组的独立性更低。软组织、骨和空气腔需要分别定义，以创建用于BNCT治疗计划的目标区域的准确三维（3D）头部模型。束流模型的准确性可以粗略估计与体内剂量，这是建议使用在超热中子设施根据新的协议。的
The epithermal neutron beam model of the Finnish boron neutron capture therapy (BNCT) facility (FiR 1) was created using the two-dimensional (2D) discrete ordinates transport (DORT) code. The final design of the beam was achieved using the DORT model: the optimal thickness of the neutron moderator and the length and the thickness of the bismuth collimator of the beam were calculated. The final beam model was validated experimentally with dosimetric measurements. The computed neutron beam spectrum was first verified with activation measurements free in air. Suitable brain tissue substitutes for neutron capture therapy (NCT) dosimetry were examined. The computed thermal neutron fluence [and gold (Au) and manganese (Mn) activation reaction rates], the gamma dose and the fast neutron dose distributions in the three tissue substitute (TS) phantoms were verified with activation and pair ionisation chamber measurements. The simplified neutron-photon beam model for the treatment planning system (TPS) was determined from the DORT model. The TPS beam model was experimentally validated in the three TS phantoms. The beam model was normalised to the Au activation measurements at the thermal neutron maximum in the PMMA (polymethylmethacrylate) phantom, which gave a link to the monitor units. The planned radiation dose in the TPS is given in monitor units. The experimentally verified beam model was first applied in the computations of the dose plans of the dog brain and in the treatment planning of glioblastoma multiforme (GBM) patients in the Finnish BNCT project. The 2D cylinder symmetrical horizontal DORT model of the FiR 1 epithermal neutron beam was observed to be an effective and reliable tool for examining the effects of different geometrical structures (moderator, collimator) on neutron and photon spectra. Of the simple phantom materials, PMMA was found to simulate the thermal neutron fluence at its maximum in the brain tissue 3 percentage units closer than water in the collimated epithermal neutron beam. However, water simulated the absorbed gamma dose in the brain tissue 12 percentage units closer than PMMA. In addition, a brain tissue equivalent liquid was designed. Parallel verification of the beam model in water, PMMA and the brain equivalent liquid confirmed reliability of the NCT dose computation. The DORT beam model was sufficiently accurate (intensity correction 5%) to use as a beam model in TPS. The beam model was normalised at the thermal neutron maximum in the PMMA phantom with the Au activation measurements. The use of the calculated Au activation reaction rate (variation 3%) for the normalisation was found to be less independent of the energy grouping of cross sections than the calculated Mn activation reaction rate (variation 13%). The soft tissue, bone and air cavities need to be defined separately to create an accurate threedimensional (3D) head model of the target area for the BNCT treatment planning. The accuracy of the beam model can be roughly estimated with in vivo dosimetry, which is recommended for use at epithermal neutron facilities in accordance with new protocols. The