Rajasekaran Dhanabalan, Jeevanandam Prakash, Sukumar Prabakar, Ranganathan Arulpandiyan, Johnjothi Samdevakumar, Nagarajan Vivekanandan
Department of Medical Physics, Cancer Institute (WIA), Chennai, India.
Department of Medical Physics, Cancer Institute (WIA), Chennai, India.
Med Dosim. 2014 Winter;39(4):300-8. doi: 10.1016/j.meddos.2014.05.002. Epub 2014 Jun 6.
In this study, we investigated the correlation between 2-dimensional (2D) and 3D gamma analysis using the new PTW OCTAVIUS 4D system for various parameters. For this study, we selected 150 clinically approved volumetric-modulated arc therapy (VMAT) plans of head and neck (50), thoracic (esophagus) (50), and pelvic (cervix) (50) sites. Individual verification plans were created and delivered to the OCTAVIUS 4D phantom. Measured and calculated dose distributions were compared using the 2D and 3D gamma analysis by global (maximum), local and selected (isocenter) dose methods. The average gamma passing rate for 2D global gamma analysis in coronal and sagittal plane was 94.81% ± 2.12% and 95.19% ± 1.76%, respectively, for commonly used 3-mm/3% criteria with 10% low-dose threshold. Correspondingly, for the same criteria, the average gamma passing rate for 3D planar global gamma analysis was 95.90% ± 1.57% and 95.61% ± 1.65%. The volumetric 3D gamma passing rate for 3-mm/3% (10% low-dose threshold) global gamma was 96.49% ± 1.49%. Applying stringent gamma criteria resulted in higher differences between 2D planar and 3D planar gamma analysis across all the global, local, and selected dose gamma evaluation methods. The average gamma passing rate for volumetric 3D gamma analysis was 1.49%, 1.36%, and 2.16% higher when compared with 2D planar analyses (coronal and sagittal combined average) for 3mm/3% global, local, and selected dose gamma analysis, respectively. On the basis of the wide range of analysis and correlation study, we conclude that there is no assured correlation or notable pattern that could provide relation between planar 2D and volumetric 3D gamma analysis. Owing to higher passing rates, higher action limits can be set while performing 3D quality assurance. Site-wise action limits may be considered for patient-specific QA in VMAT.
在本研究中，我们使用新的PTW OCTAVIUS 4D系统，针对各种参数研究了二维（2D）和三维（3D）伽马分析之间的相关性。在本研究中，我们选择了150个临床批准的头颈部（50个）、胸部（食管）（50个）和盆腔（宫颈）（50个）部位的容积调强弧形放疗（VMAT）计划。创建了各个验证计划并将其传送到OCTAVIUS 4D体模。使用全局（最大值）、局部和选定（等中心）剂量方法，通过2D和3D伽马分析比较测量和计算的剂量分布。对于常用的3毫米/3%标准和10%的低剂量阈值，在冠状面和矢状面进行2D全局伽马分析的平均伽马通过率分别为94.81%±2.12%和95.19%±1.76%。相应地，对于相同标准，3D平面全局伽马分析的平均伽马通过率为95.90%±1.57%和95.61%±1.65%。对于3毫米/3%（10%低剂量阈值）全局伽马分析，容积3D伽马通过率为96.49%±1.49%。应用严格的伽马标准会导致在所有全局、局部和选定剂量伽马评估方法中，2D平面和3D平面伽马分析之间的差异更大。对于3毫米/3%全局、局部和选定剂量伽马分析，容积3D伽马分析的平均伽马通过率分别比2D平面分析（冠状面和矢状面综合平均值）高1.49%、1.36%和2.16%。基于广泛的分析和相关性研究，我们得出结论，在平面2D和容积3D伽马分析之间不存在能提供关联的确切相关性或显著模式。由于通过率较高，在进行3D质量保证时可以设置更高的行动限值。对于VMAT中的患者特定质量保证，可考虑按部位设置行动限值。
