Clinical Implementation of VMAT
P Kapur1*, D Kahler2, C Liu2, R Kapoor3, (1) ,Richmond, VA, (2) Univ Florida, Gainesville, FL, (3) VCU Health System, Richmond, VASU-E-T-379 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: The goal of this study is to evaluate the impact of VMAT planning parameters on plan quality and delivery efficiency on linear accelerators.
Methods: VMAT technology provide a number of variable on treatment delivery such as MLC motion, dose rate (DR) and gantry rotation speed. Three parameters₋Leaf Speed (LS), Minimum DR and Control points (CP) were chosen to evaluate their impact on the VMAT plan quality and delivery efficiency. Five prostate cases were selected to generate several VMAT plans on Pinnacle TPS (v9.2) with Elekta LINAC (Synergy-S).
Leaf Speed: Pinnacle provides options for maximum LS while optimizing a treatment plan. We chose 3 LS for a comparative study 2cm/sec (maximum LS allowed at LINAC), 1.5cm/sec & 1cm/sec.
Minimum DR: Due to varying DR we evaluated the minimum DR that can be used to perform and deliver a treatment plan on the LINAC.
Control points: TPS provides 3 options for choosing the number of CP 91, 121 & 181 i.e. CP generated with gantry spacing 4°, 3°, 2° in a single arc.
Results: Leaf Speed: Due to LS impact of treatment delivery time, it is recommended to stay below the maximum LS of LINAC to avoid beam cut⁻off. The optimum LS was found as 1.5cm/sec.
Minimum DR: Beam cut⁻off issue occurred on LINAC when the DR fell below 30MU/sec. So it becomes important to choose a higher value of DR while optimizing a plan in TPS.
Control points: The number of CP used to generate a treatment plan has a minimal impact on plan quality and huge impact on plan delivery because it increases the optimization and delivery time.
Conclusion: Each parameter in the above study has different impact on the plan quality & delivery efficiency. Hence it is important to evaluate all the parameters before clinical VMAT implementation.