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Knowledge-Based VMAT Planning for Comprehensive Irradiation of Breast/Chest Wall and Locoregional Nodes

R Mahon1*, M Schmidt1, E Pryser1, C Bertelsman2, J Rolfingsmeier2, J Schremp2, J Watkins2, M Thomas1, I Zoberi1, F Reynoso1, (1) Washington University in St. Louis, St. Louis, MO, (2) Barnes-jewish Hospital, St. Louis, MO


PO-BPC-Virtual-39 (Saturday, 4/17/2021)   [Eastern Time (GMT-4)]

Purpose: VMAT planning provides highly conformal dose distributions and increased delivery speed when compared to 3D techniques. Knowledge-based VMAT planning for comprehensive breast/chest-wall irradiation can spare heart and ipsilateral lung while providing improved coverage to the internal mammary nodes (IMN) without adversely affecting low dose constraints on contralateral lung.

Methods: A knowledge-based RapidPlan model was constructed using 155 IMRT comprehensive breast treatment plans. A standard VMAT technique was developed to spare the heart and ipsilateral lung as much as possible without sacrificing coverage to the IMN. The technique is compared against the RTOG 1304 Group 2-Arm2A benchmark case using standard fractionation. The dose distribution for 65 comprehensive breast and chest-wall plans treated in our institution in 2019-2021 using a hypofractionated approach were analyzed for the following dose metrics: V95% of combined PTV, dose homogeneity index (D95%/D5%), RTOG conformity index, and adherence to the Alliance A221505 trial constraints.

Results: The VMAT plan technique was able to successfully meet all of the RTOG 1304 Group 2-Arm2A constraints on the benchmark case with a mean heart dose of 2.96Gy, ipsilateral lung V20Gy=22.7%, and V5Gy=6.44%/8.84% for contralateral lung/breast while achieving V95% > 96.7% for all PTVs. The evaluation of the clinical cases showed an average: mean heart dose of 416.3±102.16cGy for LT-sided targets and 286.1±73.64cGy for RT-sided targets, ipsilateral lung V18Gy of 21.8%±5.77%, contralateral lung V4.8Gy of 15.4%±5.37%. Average total PTV coverage of 95% RX was to 98.8%±1.01 of volume with an average conformity and dose heterogeneity of 1.2±0.10 and 0.92±0.02 respectively.

Conclusion: VMAT breast planning can consistently help reduce heart and ipsilateral lung doses for comprehensive breast irradiation of the whole breast/chest-wall and locoregional nodes; while achieving highly conformal and homogeneous dose to the target and only a minor and acceptable increase to low dose constraints to the contralateral OARs.

Funding Support, Disclosures, and Conflict of Interest: Mr. Schmidt reports personal consulting fees and honoraria with Varian Medical Systems outside of the submitted work. Remaining authors have no conflicts to disclose.


Breast, Heart, Lung


TH- External Beam- Photons: Treatment planning using machine learning/Knowledge Based Planning/automation

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