Background

Dosimetric validation of single isocenter multi-target radiosurgery plans is difficult due to conditions of electronic disequilibrium and the simultaneous irradiation of multiple off-axis lesions dispersed throughout the volume. Here we report the benchmarking of a customizable Monte Carlo secondary dose calculation algorithm specific for multi-target radiosurgery which future users may use to guide their commissioning and clinical implementation.

Purpose

To report the generation, validation, and clinical benchmarking of a volumetric Monte Carlo (MC) dose calculation beam model for single isocenter radiosurgery of intracranial multi-focal disease.

Methods

The beam model was prepared within SciMoCa (ScientificRT, Munich Germany), a commercial independent dose calculation software, with the aim of broad availability via the commercial software for use with single isocenter radiosurgery. The process included (1) definition & acquisition of measurement data required for beam modeling, (2) tuning model parameters to match measurements, (3) validation of the beam model via independent measurements and end-to-end testing, and finally, (4) clinical benchmarking and validation of beam model utility in a patient specific QA setting. We utilized a 6X Flattening-Filter-Free photon beam from a TrueBeam STX linear accelerator (Siemens Healthineers, Munich Germany).

Results

In addition to the measured data required for standard IMRT/VMAT (depth dose, central axis profiles & output factors, leaf gap), beam modeling and validation for single-isocenter SRS required central axis and off axis (5 cm & 9 cm) small field output factors and comparison between measurement and simulation of backscatter with aperture for jaw much greater than MLCs. Validation end-to-end measurements included SRS MapCHECK in StereoPHAN geometry (2%/1 mm Gamma = 99.2% ± 2.2%), and OSL & scintillator measurements in anthropomorphic STEEV phantom (6 targets, volume = 0.1–4.1cc, distance from isocenter = 1.2–7.9 cm) for which mean difference was −1.9% ± 2.2%. For 10 patient cases, MC for individual PTVs was −0.8% ± 1.5%, −1.3% ± 1.7%, and −0.5% ± 1.8% for mean dose, D_95%, and D_1%, respectively. This corresponded to custom passing rates action limits per AAPM TG-218 guidelines of ±5.2%, ±6.4%, and ±6.3%, respectively.

Conclusions

The beam modeling, validation, and clinical action criteria outlined here serves as a benchmark for future users of the customized beam model within SciMoCa for single isocenter radiosurgery of multi-focal disease.

中文翻译：

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用于多目标 SRS 的商业独立蒙特卡洛计算波束模型的生成、验证和基准测试

背景

由于电子不平衡的情况以及分散在整个体积中的多个离轴病灶的同时照射，单等中心多目标放射外科计划的剂量学验证很困难。在这里，我们报告了专门针对多目标放射外科的可定制蒙特卡罗二次剂量计算算法的基准测试，未来的用户可以使用它来指导他们的调试和临床实施。

目的

报告用于颅内多病灶疾病单等中心放射外科的体积蒙特卡罗 (MC) 剂量计算射束模型的生成、验证和临床基准测试。

方法

射束模型是在 SciMoCa（ScientificRT，德国慕尼黑）中准备的，这是一种商业独立剂量计算软件，目的是通过商业软件广泛应用于单等中心放射外科。该过程包括 (1) 定义和获取梁建模所需的测量数据，(2) 调整模型参数以匹配测量结果，(3) 通过独立测量和端到端测试验证梁模型，最后，( 4) 在患者特定的 QA 设置中对光束模型实用性进行临床基准测试和验证。我们使用来自 TrueBeam STX 线性加速器（德国慕尼黑西门子 Healthineers）的 6 倍无平坦滤波器光子束。

结果

除了标准 IMRT/VMAT 所需的测量数据（深度剂量、中心轴轮廓和输出因子、叶间隙）外，单等中心 SRS 的射束建模和验证还需要中心轴和离轴（5 cm 和 9 cm）小场输出因子以及反向散射测量与模拟之间的比较，钳口孔径远大于 MLC。验证端到端测量包括 StereoPHAN 几何结构中的 SRS MapCHECK（2%/1 mm Gamma = 99.2% ± 2.2%），以及拟人化 STEEV 体模中的 OSL 和闪烁体测量（6 个目标，体积 = 0.1–4.1cc，距离等中心= 1.2-7.9 cm），平均差为-1.9% ± 2.2%。_{对于 10 例患者病例，平均剂量、D 95%}和 D _1%的各个 PTV 的 MC 分别为 -0.8% ± 1.5%、-1.3% ± 1.7% 和 -0.5% ± 1.8% 。这对应于 AAPM TG-218 指南的自定义通过率行动限制，分别为 ±5.2%、±6.4% 和 ±6.3%。

结论

这里概述的射束建模、验证和临床行动标准可作为 SciMoCa 中用于多病灶疾病的单等中心放射外科定制射束模型的未来用户的基准。