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Flattening Filter-Free Volumetric Modulation Arc Therapy for Post-Mastectomy Breast Irradiation

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D Heins

D Heins1*, J Yoon2 , B Guo2 , M Sanders3 , R Zhang2,3 , (1) CARTI, Inc., Little Rock, AR, (2) Louisiana State University, Baton Rouge, LA, (3) Mary Bird Perkins Cancer Center, Baton Rouge, LA


SU-I-GPD-T-501 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To determine if flattening filter-free volumetric modulated arc therapy (FFF-VMAT) can maintain equal or better dose coverage than standard VMAT while reducing doses to organs at risk (OARs) for post-mastectomy radiotherapy (PMRT).

Methods: FFF-VMAT with different beam energies (6x and 10x) were produced for ten PMRT patients previously treated at our clinic with standard VMAT. Both VMAT (6x) and FFF-VMAT (6x and 10x) treatment plans were created on a commercial TPS (Pinnacle v9.8, Philips Medical Systems, Fitchburg, WI). All the plans used a prescribed dose of 50.0 Gy in 25 fractions, 0 degree couch angle and 45 degree collimator angle. Every technique was planned using its maximum dose rate: VMAT (6x) used 600 Monitor Units (MU) per minute, FFF-VMAT6x used 1200 MU per minute, and FFF-VMAT10x used 2000 MU per minute. Each plan also utilized two partial arcs and each arc covered approximately 220°. Planning target volume (PTV) coverage, dose to OARs and risks of developing radiogenic side effects were evaluated. The total treatment time per fraction was also measured and compared.

Results: All techniques produced clinically acceptable PMRT plans and comparable tumor control probability. There was no statistically significant difference in mean lung dose and risk of developing second cancer in lung. FFF-VMAT6x conferred significantly higher mean heart dose and risk of cardiac toxicity compared to VMAT, while showing statistically significant reduction in contralateral breast dose and risk of second cancer. In addition, FFF-VMAT techniques exhibited reduced treatment times over VMAT, but the absolute time reduction was not likely to be clinically significant.

Conclusion: This work has shown that both 6x and 10x FFF-VMAT techniques are comparable to VMAT with FFF-VMAT6x having slight improvements. Patients with increased risk of radiation-induced cancer of the contralateral breast may benefit from FFF-VMAT6x.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by National Cancer Institute Award 1 K22 CA204464-01, Louisiana State University (LSU) Faculty Research Grant and LSU Economic Development Award.

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