Department of Radiation Oncology, UPMC Hillman Cancer Center, Pittsburgh, Pennsylvania, USA.
J Appl Clin Med Phys. 2022 Sep;23(9):e13710. doi: 10.1002/acm2.13710. Epub 2022 Aug 12.
Portal dosimetry is one option for verification of volumetric-modulated arc therapy (VMAT) planning for multiple brain metastases. However, due to the changing response of the portal imager with photon beam energy, the dose transmitted through closed multileaf collimator (MLC) leaves or narrow MLC gaps may be underestimated by the imager. We present a simple method for correcting for these effects that may be implemented within the Eclipse treatment planning system. We recalculated the predicted portal dose with and without this correction for 20 multiple brain met VMAT plans. Before the correction, 3/20 composite plan fields passed our standard quality assurance (QA) criteria (54/80 individual fields); the average gamma passing rate for the composite plans was 76.9 ± 16.6%, and the average gamma value across the composite plans was 0.67 ± 0.23. After correction, 20/20 composite plan fields passed the QA criteria (80/80 individual fields); the average gamma passing rate for composite plans was 99.2 ± 1.4%, the average gamma value across the composite plans was 0.33 ± 0.90. A measure of plan complexity, the average leaf pair opening could be correlated to the gamma analysis results for the uncorrected plans but not for the corrected plans.
适形调强弧形治疗（VMAT）计划多脑转移瘤的容积验证方法之一是通过门控剂量验证。然而，由于光子束能量的变化会影响到门控成像系统的响应，所以通过闭合多叶准直器（MLC）叶片或狭窄的 MLC 间隙传输的剂量可能会被低估。我们提出了一种简单的校正方法，该方法可在 Eclipse 治疗计划系统中实施。我们对 20 个多脑转移 VMAT 计划进行了校正前后的预测门控剂量的重新计算。校正前，有 3/20 个复合野通过了我们的标准质量保证（QA）标准（80 个单个野中有 54 个）；复合计划的平均伽马通过率为 76.9%±16.6%，复合计划的平均伽马值为 0.67±0.23。校正后，20/20 个复合野通过了 QA 标准（80 个单个野中 80 个）；复合计划的平均伽马通过率为 99.2%±1.4%，复合计划的平均伽马值为 0.33±0.90。叶对平均开口是计划复杂性的一个衡量标准，与未校正计划的伽马分析结果相关，但与校正后的计划无关。
