Independent dose verification system with Monte Carlo simulations using TOPAS for passive scattering proton therapy at the National Cancer Center in Korea
Independent dose verification system with Monte Carlo simulations using TOPAS for passive scattering proton therapy at the National Cancer Center in Korea
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DOI：
10.1088/1361-6560/aa8663
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发表时间：
2017-10-07
影响因子：
3.5
通讯作者：
Min, Chul Hee
中科院分区：
文献类型：
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作者：
Shin, Wook-Geun;Testa, Mauro;Min, Chul Hee
为了独立验证治疗计划，我们开发了一个全自动蒙特卡罗（MC）为基础的病人剂量计算系统，粒子模拟（TOPAS）工具和质子治疗机安装在韩国国家癌症中心，使每个病人的常规和自动剂量重新计算。利用TOPAS软件对质子束喷嘴进行建模，模拟治疗光束，并通过对比深度剂量百分比与测量值进行MC调试。根据规定的波束范围和调制宽度进行波束设置，通过修改供应商特定的方法实现自动化。CT幻影基于内置topas功能的DICOM CT文件建模，由公司自行开发的c++代码直接导入定位CT幻影的CT文件、模拟治疗方案的RT-plan文件和应用Hounsfield unit （HU）分配的RT-structure文件。通过将该系统与治疗计划系统（TPS）计算的剂量分布进行比较，对1例肺幻影和2例腹部和乳腺内淋巴结患者进行了验证。波束调试的结果与B8选项在波束范围和扩展布拉格峰的调制宽度上的一致性很好，高达0.8 mm(2) g（-1）。相对于B5选项任意点的规定范围和调制(128.3、132.0和141.2 mm（2) g（-1）的范围），波束设置技术可以分别以0.06%和0.51%的精度预测范围和调制宽度。MC模拟与靶区临床TPS的三维伽马指数（距离一致3 mm，剂量差3%）通过率高于99%。然而，在正常组织中，肺幻象和乳腺内淋巴结病例的放射治疗方案不太一致。这种差异可能是由于临床TPS在距离补偿器和非均匀材料中存在局限性，TPS是一种不准确的散射效应剂量计算算法。此外，补偿器的陡坡、HU值转换为人体幻影以及HU分配的剂量计算算法也可能是导致差异的原因。目前的研究可用于治疗方案的独立剂量验证，包括高不均匀性，陡峭的补偿器和风险，如肺，头颈部病例。根据治疗政策，MC预测的剂量差异可用于原治疗计划的接受决策。
For the independent validation of treatment plans, we developed a fully automated Monte Carlo (MC)-based patient dose calculation system with the tool for particle simulation (TOPAS) and proton therapy machine installed at the National Cancer Center in Korea to enable routine and automatic dose recalculation for each patient. The proton beam nozzle was modeled with TOPAS to simulate the therapeutic beam, and MC commissioning was performed by comparing percent depth dose with the measurement. The beam set-up based on the prescribed beam range and modulation width was automated by modifying the vendor-specific method. The CT phantom was modeled based on the DICOM CT files with TOPAS-built-in function, and an in-house-developed C++ code directly imports the CT files for positioning the CT phantom, RT-plan file for simulating the treatment plan, and RT-structure file for applying the Hounsfield unit (HU) assignment, respectively. The developed system was validated by comparing the dose distributions with those calculated by the treatment planning system (TPS) for a lung phantom and two patient cases of abdomen and internal mammary node. The results of the beam commissioning were in good agreement of up to 0.8 mm(2) g(-1) for B8 option in both of the beam range and the modulation width of the spread-out Bragg peaks. The beam set-up technique can predict the range and modulation width with an accuracy of 0.06% and 0.51%, respectively, with respect to the prescribed range and modulation in arbitrary points of B5 option (128.3, 132.0, and 141.2 mm(2) g(-1) of range). The dose distributions showed higher than 99% passing rate for the 3D gamma index (3 mm distance to agreement and 3% dose difference) between the MC simulations and the clinical TPS in the target volume. However, in the normal tissues, less favorable agreements were obtained for the radiation treatment planning with the lung phantom and internal mammary node cases. The discrepancies might come from the limitations of the clinical TPS, which is the inaccurate dose calculation algorithm for the scattering effect, in the range compensator and inhomogeneous material. Moreover, the steep slope of the compensator, conversion of the HU values to the human phantom, and the dose calculation algorithm for the HU assignment also could be reasons of the discrepancies. The current study could be used for the independent dose validation of treatment plans including high inhomogeneities, the steep compensator, and riskiness such as lung, head & neck cases. According to the treatment policy, the dose discrepancies predicted with MC could be used for the acceptance decision of the original treatment plan.