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Comparison of Two VMAT Planning Techniques Using Planned and Delivered Dose Distributions

D Mathew

D Mathew*, S Edlund , Y Watanabe , University of Minnesota, Minneapolis, MN


SU-I-GPD-T-371 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: VMAT plans were generated by optimizing two beams and compared against the option in Pinnacle to add an additional arc given a single initial beam. This study intends to determine which planning option provides the best plan based on the dose to critical structures and the quality of the delivered dose distributions.

Methods: Seven prostate patients were planned using Pinnacle v14 to a dose of 45Gy. The VMAT plans were calculated for a Varian TrueBeam. Each patient was planned twice: once using two manually added beams with full, 360-degree arcs (2Beam2Arcs), and secondly with one full arc beam which was set to allow an additional arc during optimization (1Beam2Arcs). Each plan was calculated with the identical dose constraints using Pinnacle’s auto planning method in order to improve objectivity. The plans were evaluated in Pinnacle based on rectal and bladder DVHs at 25%, 50%, and 75% volume. Normal tissue mean dose was also compared, in addition to conformity index (CI) and homogeneity index (HI). We performed plan QA using the Sun Nuclear ArcCheck. 3DVH was used to determine actually delivered doses to rectum and bladder.

Results: Homogeneity indices were higher for the 1Beam2Arc plans; however the CI values were not significantly different. The 1Beam1Arc plans reduced dose to bladder and rectum, though within statistical uncertainty. However, using 3DVH to compare the delivery of each type of plan, we see that there is generally reduced dose to rectum and bladder. Gamma analysis was identical for each plan type (3%/3mm).

Conclusion: Planning using 1Beam2Arcs seems to be at least as good as the 2Beam2Arc approach, with gamma analysis of the two plan types essentially identical. The current results suggest that both planned and delivered rectal and bladder doses were reduced using 1Beam2Arc planning, indicating that this would be the preferred planning method.

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