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Comparison of Optimization Methods for Stereotactic Radiosurgery (SRS) of Brain Metastases

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H Liu

D Wiant1 , J Maurer2 , B Sintay3 , K Pearman4 , Q Shang5 , T Hayes6 , H Liu7*, (1) Cone Health Cancer Center, Greensboro, NC, (2) Cone Health Cancer Center, Greensboro, NC, (3) Cone Health, Summerfield, NC, (4) Cone health cancer center, Greensboro, NC, (5) ,Greensboro, NC, (6) Cone Health Cancer Center, Greensboro, NC, (7) Cone Health Cancer Center, Greensboro, NC


SU-I-GPD-T-563 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The photon optimization (PO) algorithm was recently released by Varian Medical Systems to improve, among other things, volumetric modulated arc therapy (VMAT) optimization within Eclipse (V15). The purpose of this study is to compare the PO algorithm with its predecessor, the progressive resolution optimizer (PRO) for brain metastasis.

Methods: Seven patients with a total of 9 targets treated to 25Gy in 5 fractions were selected retrospectively. Previously, all the plans were developed with the PRO algorithm. In the PO algorithm, dynamic conformal arcs (DCA) are first conformed to the target, and VMAT inverse planning is performed to achieve the desired dose distributions. PTV coverage was forced to at least 99% for each patient for a fair comparison. Plan quality was assessed based on the conformity index (CI) for the PTV and normal tissue volumes encompassed by the 12 and 6 Gy isodose lines (V12 and V6). The modulation complexity score (MCS) was calculated (the larger the MCS, the less of the plan complexity), and the correlation of MCS, total MU used, and gamma passing rates (using 5%/1mm and 10% threshold criteria) were studied.

Results: The average CI was 1.25±0.14 and 1.26±0.19 for PO and PRO plans, respectively. No difference between two algorithms was found for the ratio of V12 and V6 (0.97±0.09 and 1.01±0.09). Significant improvements in the gamma passing rate (increased from 96.7%±2.8% to 98.6%±1.8%), MLC modulation (MCS increased from 0.30±0.07 to 0.38±0.06), and delivery efficiency (MU reduction of 31%±12%) were found for the new PO method. The MCS showed a strong correlation with the gamma passing rate, and an inverse correlation with the total MU used.

Conclusion: The new PO algorithm offers comparable plan quality to the PRO, while minimizing MLC complexity, thereby improving the delivery efficiency and QA results.

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