Kum O, Shin H, Han Y
Konyang University, Medical Science College and Konyang University Hospital, DAEJON, Korea.
Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Med Phys. 2012 Jun;39(6Part11):3730. doi: 10.1118/1.4735177.
Wide spread clinical use of advanced radiation treatment delivery techniques such as volumetric modulated arc therapy (VMAT) and IMRT needs an easy-to-use, well-defined, and effective quality assurance (QA) system to ensure the accuracy of dose delivery. The comprehensive evaluation of two delivery QA systems (DQA) (Portal Dosimetry and Compass) for the advanced radiation delivery techniques is necessary for the clinical setting.
Portal Dosimetry QA system with Varian PortalVision (PV) provides a quantitative comparison of measured electronic dose profile to a predicted dose profile with Varian's Eclipse™ treatment planning system (TPS) for the VMAT and IMRT plans. Quantitative comparisons of the two images, including dose difference, gamma analysis, points dose measurements, and line profiles are easily acquired in two dimensions. Meanwhile, Compass system with MatriXX can provide an accurate three-dimensional quantitative analysis of dose delivery. We applied the two planning QA systems to our RapidArc patient- specific QAs. Validation of the Compass and Portal Dosimetry systems were performed with ionization chamber measurements for absolute dosimetry and film measurements for gamma index calculations for phantom and patient treatment plans.
Compass system was very sensitive to the MLC leaf gap variations in three dimensional gamma analyses. However, Compass system was not enough to fix the errors in dosimetric leaf gap by itself. DQA process with Portal Dosimetry took approximately 6 minutes for the two Arcs VMAT plan. Compass took about 40 minutes for the same plan in our first clinical trial. For the three typical IMRT and VMAT plans, the two systems showed the same passing rates in 95% pixels passing gamma criteria 3%/3mm.
Portal Dosimetry DQA system has the advantages of effectiveness and practicality in the clinical setting. On the other hand, Compass was the next supportive system because of its accuracy and reality with patient's anatomy.
容积调强弧形放疗（VMAT）和调强放疗（IMRT）等先进放射治疗技术在临床广泛应用，需要一个易于使用、定义明确且有效的质量保证（QA）系统来确保剂量传递的准确性。对于临床环境而言，对这两种先进放射治疗技术的剂量传递QA系统（DQA）（射野剂量测定和Compass）进行全面评估是必要的。
带有瓦里安PortalVision（PV）的射野剂量测定QA系统，针对VMAT和IMRT计划，将测量的电子剂量分布与瓦里安Eclipse™治疗计划系统（TPS）预测的剂量分布进行定量比较。在二维空间中可轻松获取两幅图像的定量比较结果，包括剂量差异、伽马分析、点剂量测量和线轮廓。同时，带有MatriXX的Compass系统可对剂量传递进行精确的三维定量分析。我们将这两种计划QA系统应用于我们的针对患者的容积弧形调强放疗快速质量保证中。通过电离室测量进行绝对剂量测定，并通过胶片测量进行体模和患者治疗计划的伽马指数计算，对Compass和射野剂量测定系统进行验证。
在三维伽马分析中，Compass系统对多叶准直器（MLC）叶片间隙变化非常敏感。然而，Compass系统自身不足以校正剂量测定叶片间隙中的误差。对于两弧VMAT计划，使用射野剂量测定的DQA过程大约需要6分钟。在我们的首次临床试验中，对于相同计划，Compass大约需要40分钟。对于三种典型的IMRT和VMAT计划，在95%像素通过3%/3mm伽马标准方面，这两种系统显示出相同的通过率。
射野剂量测定DQA系统在临床环境中具有有效性和实用性的优点。另一方面，Compass因其对患者解剖结构的准确性和真实性而成为下一个辅助系统。
