Development of Plan Complexity Mitigation Algorithm for VMAT
T Ono1*, M Nakamura2, T Mizowaki1, (1)Department of Radiation Oncology and Image-applied Therapy, Graduate School of Medicine, Kyoto University, Kyoto, Japan, (2) Division of Medical Physics, Department of Information Technology and Medical Engineering, Human Health Sciences, Kyoto University Graduate School of Medicine, Kyoto, Japan
Presentations
MO-IePD-TRACK 5-4 (Monday, 7/26/2021) 5:30 PM - 6:00 PM [Eastern Time (GMT-4)]
Purpose: The purpose of this study was to develop an algorithm to mitigate plan complexity in volumetric-modulated arc therapy (VMAT) and to evaluate its usefulness.
Methods: Twenty patients who underwent VMAT (including seven Dynamic WaveArc plans) between September 2015 and December 2020 were enrolled in this study. Clinical sites included the brain (n=6), head and neck (n=2), lungs (n=3), esophagus (n=3), whole pelvis (n=3), and prostate (n=3). Patients with less than 85% gamma passing rate (GPR) of 3%/2mm were arbitrarily selected. Using the GPR prediction model we previously developed, we identified the leaf positions responsible for the decrease in GPR. Using a limited nonlinear algorithm, the multi-leaf collimator (MLC) positions were optimized within the mechanical limitations. The dose prescription for the target was re-normalized, and the monitor unit (MU) was modified. The Modulated Complexity Score (MCS), average aperture area (AA: mm2), and MU/Gy were evaluated to determine the difference in plan complexity between the optimized and original plans. The calculated doses were evaluated for the target and surrounding organs. Additionally, the ArcCHECK cylindrical diode array was used to measure the dose, and GPR (5%/1 mm) and GPR (3%/2 mm) were evaluated to determine the difference between the optimized and original plans. Differences were presented as means ± standard deviations.
Results: The differences in plan complexity parameters between the optimized and original plans were 4.3±2.7×10-3 for MCS, 67.6±113.3 mm2 for AA, and -0.3±1.3 MU/Gy, respectively. For the calculated dose, dose volume histograms were within 1% for the target and surrounding organs. The difference of GPR between optimized and original plans were 0.9±1.1%point (%p) for GPR (5%/1 mm) and 1.0±1.8%p for GPR (3%/2 mm). The GPRs were slightly improved with the optimized plans.
Conclusion: The developed algorithm could mitigate plan complexity and improve GPR with minor leaf position modifications for VMAT.
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