Zhang Dandan, Wang Bin, Zhang Guangshun, Ma Charlie, Deng Xiaowu
Department of Radiation Oncology, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, China.
School of Physics, Sun Yat-sen University, Guangzhou, China.
J Appl Clin Med Phys. 2018 Jul;19(4):230-238. doi: 10.1002/acm2.12389. Epub 2018 Jun 15.
This study compared three-dimensional (3D) and two-dimensional (2D) percentage gamma passing rates (%GPs) for detection sensitivity to IMRT delivery errors and investigated the correlation between two kinds of %GP. Eleven prostate IMRT cases were selected, and errors in multileaf collimator (MLC) bank sag, MLC leaf traveling, and machine output were simulated by recalculating the dose distributions in patients. 2D doses were extracted from the 3D doses at the isocenter position. The 3D and 2D %GPs with different gamma criteria were then obtained by comparing the recalculated and original doses in specific regions of interest (ROI), such as the whole body, the planning target volume (PTV), the bladder, and the rectum. The sensitivities to simulated errors of the two types of %GP were compared, and the correlation between the 2D and 3D %GPs for different ROIs were analyzed. For the whole-body evaluation, both the 2D and 3D %GPs with the 3%/3 mm criterion were above 90% for all tested MLC errors and for MU deviations up to 4%, and the 3D %GP was higher than the 2D %GP. In organ-specific evaluations, the PTV-specific 2D and 3D %GP gradients were -4.70% and -5.14% per millimeter of the MLC traveling error, and -17.79% and -20.50% per percentage of MU error, respectively. However, a stricter criterion (2%/1 mm) was needed to detect the tested MLC sag error. The Pearson correlation analysis showed a significant strong correlation (r > 0.8 and P < 0.001) between the 2D and 3D %GPs in the whole body and PTV-specific gamma evaluations. The whole-body %GP with the 3%/3 mm criterion was inadequate to detect the tested MLC and MU errors, and a stricter criterion may be needed. The PTV-specific gamma evaluation helped to improve the sensitivity of the error detection, especially using the 3D GP%.
本研究比较了三维（3D）和二维（2D）百分比伽马通过率（%GPs）对调强放疗（IMRT） delivery errors的检测敏感性，并研究了两种%GP之间的相关性。选择了11例前列腺IMRT病例，通过重新计算患者体内的剂量分布，模拟了多叶准直器（MLC） bank sag、MLC叶片移动和机器输出的误差。在等中心位置从3D剂量中提取2D剂量。然后通过比较特定感兴趣区域（ROI）（如全身、计划靶区（PTV）、膀胱和直肠）中重新计算的剂量和原始剂量，获得具有不同伽马标准的3D和2D %GPs。比较了两种类型%GP对模拟误差的敏感性，并分析了不同ROI的2D和3D %GPs之间的相关性。对于全身评估，对于所有测试的MLC误差和高达4%的MU偏差，采用3%/3 mm标准的2D和3D %GPs均高于90%，且3D %GP高于2D %GP。在器官特异性评估中，PTV特异性2D和3D %GP梯度分别为每毫米MLC移动误差-4.70%和-5.14%，以及每百分比MU误差-17.79%和-20.50%。然而，需要更严格的标准（2%/1 mm）来检测测试的MLC sag误差。Pearson相关分析表明，在全身和PTV特异性伽马评估中，2D和3D %GPs之间存在显著的强相关性（r > 0.8且P < 0.001）。采用3%/3 mm标准的全身%GP不足以检测测试的MLC和MU误差，可能需要更严格 的标准。PTV特异性伽马评估有助于提高误差检测的敏感性，尤其是使用3D GP%时。 （注：原文中“IMRT delivery errors”这里的“delivery”不太明确准确意思，可能是“传输、递送”等相关含义，结合语境大致如此翻译，整体翻译可能因这个词在医学上准确含义不确定而有细微偏差）
