Background

The recent availability of Monte Carlo based independent secondary dose calculation (ISDC) for patient-specific quality assurance (QA) of modulated radiotherapy requires the definition of appropriate, more sensitive action levels, since contemporary recommendations were defined for less accurate ISDC dose algorithms.

Purpose

The objective is to establish an optimum action level and measure the efficacy of a Monte Carlo ISDC software for pre-treatment QA of intensity modulated radiotherapy treatments.

Methods

The treatment planning system and the ISDC were commissioned by their vendors from independent base data sets, replicating a typical real-world scenario. In order to apply Receiver-Operator-Characteristics (ROC), a set of treatment plans for various case classes was created that consisted of 190 clinical treatment plans and 190 manipulated treatment plans with dose errors in the range of 1.5–2.5%. All 380 treatment plans were evaluated with ISDC in the patient geometry. ROC analysis was performed for a number of Gamma (dose-difference/distance-to-agreement) criteria. QA methods were ranked according to Area under the ROC curve (AUC) and optimum action levels were derived via Youden’s J statistics.

Results

Overall, for original treatment plans, the mean Gamma pass rate (GPR) for Gamma(1%, 1 mm) was close to 90%, although with some variation across case classes. The best QA criterion was Gamma(2%, 1 mm) with GPR > 90% and an AUC of 0.928. Gamma criteria with small distance-to-agreement had consistently higher AUC. GPR of original treatment plans depended on their modulation degree. An action level in terms of Gamma(1%, 1 mm) GPR that decreases with modulation degree was the most efficient criterion with sensitivity = 0.91 and specificity = 0.95, compared with Gamma(3%, 3 mm) GPR > 99%, sensitivity = 0.73 and specificity = 0.91 as a commonly used action level.

Conclusions

ISDC with Monte Carlo proves highly efficient to catch errors in the treatment planning process. For a Monte Carlo based TPS, dose-difference criteria of 2% or less, and distance-to-agreement criteria of 1 mm, achieve the largest AUC in ROC analysis

中文翻译：

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基于蒙特卡罗的独立二次剂量计算的灵敏度和特异性，用于检测调强放射治疗中与调制相关的剂量误差

背景

最近，基于蒙特卡罗的独立二次剂量计算（ISDC）可用于患者特定的调制放射治疗质量保证（QA），需要定义适当的、更敏感的行动水平，因为当代的建议是针对不太准确的 ISDC 剂量算法定义的。

目的

目的是建立最佳作用水平并测量蒙特卡罗 ISDC 软件对调强放射治疗的治疗前 QA 的功效。

方法

治疗计划系统和 ISDC 是由其供应商根据独立的基础数据集委托的，复制了典型的现实世界场景。为了应用接受者-操作者-特征（ROC），针对不同病例类别创建了一套治疗计划，其中包括 190 个临床治疗计划和 190 个剂量误差在 1.5-2.5% 范围内的操纵治疗计划。所有 380 个治疗计划均根据患者几何形状使用 ISDC 进行了评估。针对许多 Gamma（剂量差异/一致性距离）标准进行了 ROC 分析。QA 方法根据 ROC 曲线下面积 (AUC) 进行排名，最佳作用水平通过 Youden's J 统计数据得出。

结果

总体而言，对于原始治疗计划，Gamma(1%, 1 mm) 的平均 Gamma 通过率 (GPR) 接近 90%，尽管不同病例类别之间存在一些差异。最佳 QA 标准是 Gamma(2%, 1 mm)，GPR > 90%，AUC 为 0.928。一致性距离较小的伽玛标准始终具有较高的 AUC。原始治疗计划的GPR取决于其调制程度。与 Gamma(3%, 3 mm) GPR > 99% 相比，随着调制程度降低，以 Gamma(1%, 1 mm) GPR 表示的作用水平是最有效的标准，灵敏度 = 0.91，特异性 = 0.95 = 0.73，特异性 = 0.91 作为常用的操作水平。

结论

事实证明，采用蒙特卡罗的 ISDC 可以非常有效地发现治疗计划过程中的错误。对于基于蒙特卡罗的 TPS，剂量差异标准为 2% 或更少，距离一致性标准为 1 mm，在 ROC 分析中实现最大 AUC