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

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 (TM)). 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 MUxAA/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 MUxAA/CP were 269 degrees and 13 degrees, 269 degrees and 13 degrees, and 273 degrees and 153 degrees 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.