Effects of Mechanical Performance on Deliverability and Dose Distribution by Comparing Multi Institutions’ Knowledge-based Models for Prostate Cancer in Volumetric Modulated Arc Therapy

Abstract

Background/Aim: The aim of this study was to evaluate the mechanical performance and the effect on dose distribution and deliverability of volumetric modulated arc therapy (VMAT) plans for prostate cancer created with the commercial knowledge-based planning (KBP) system (RapidPlan™). Materials and Methods: Three institutions, A, B, and C were enrolled in this study. Each institution established and trained a KBP model with their own cases. CT data and structures for 45 patients at institution B were utilized to validate the dose-volume parameters (D 2(%) , D 95(%), and D 98(%) for target, and V 50(%) , V 75(%), and V 90(%) for rectum and bladder), and the following mechanical performance parameters and gamma passing rates of each KBP model: leaf sequence variability (LSV), aperture area variability (AAV), total monitor unit (MU), modulation complexity score for VMAT (MCSv), MU/control point (CP), aperture area (AA)/CP, and MU×AA/CP. Results: Significant differences (p<0.01) in dosimetric parameters such as D 2 and D 98 for target and V 50 , V 75, and V 90 for bladder were observed among the three institutions. The means and standard deviations of MCSv were 0.31±0.03, 0.29±0.02, and 0.32±0.03, and the angles of maximum and minimum MU×AA/CP were 269˚and 13˚, 269˚and 13˚, and 273˚and 153˚at institutions A, B, and C, respectively. The mean gamma passing rate (1%/1 mm.) was >95% for all cases in each institution. Dose distribution and mechanical performance significantly differed between the three models. Conclusion: Each KBP model had different dose distributions and mechanical performance but could create an acceptable plan for deliverability regardless of mechanical performance.Volumetric modulated arc therapy (VMAT) is an intensitymodulated technique delivered with dynamic gantry motion, while varying multi leaf collimators (MLC), dose rates, and gantry speeds (1) and can be used to create a steep dose gradient and complement dose distribution (2). It utilizes inverse planning to improve target conformity and organ at risk (OAR) sparing (3) and has often been used for prostate and head and neck cancer (4, 5). However, one of the disadvantages of VMAT is that the plan quality, such as target coverage and OAR sparing, depends on the planner's skill and experience or institution's plan policy during optimization (6, 7).VMAT plans require more complex parameters related to treatment equipment such as gantry, linear accelerator, and MLC than conformal plans; therefore, it is recommended that patient-specific quality assurance (QA) be performed prior to initiating treatment to ensure deliverability. Complexity is associated with gantry speed, MU and sequence and aperture of MLC, which we defined as 687 This article is freely accessible online.

Implementation, Dosimetric Assessment, and Treatment Validation of Knowledge-Based Planning (KBP) Models in VMAT Head and Neck Radiation Oncology

“…On the other hand, Kubo et al found increased MUs and more complicated MLC sequences compared to the clinical ones for prostate cancer patients [ 29 ]. Another study assessed the deliverability of VMAT plans for prostate cancer patients from three different institutions, and they concluded that, despite the statically significant differences in MUs or the modulation complexity score among the centers, the RapidPlan™ plans were deliverable [ 30 ].…”