Dosimetric Comparison of Commonly Used Volumetric Modulated Arc Therapy Field Arrangements Based on Flattening Filter-Free Beams for Synchronous Bilateral Breast Carcinoma Radiation Therapy.

Purpose: Flattening filter-free (FFF)-based volumetric modulated arc therapy (VMAT) has been shown to be feasible and significantly improves treatment efficiency and lung protection for synchronous bilateral breast irradiation (SBBI). This research compared the commonly used VMAT field arrangements using FFF beams.

Methods: Twenty-eight patients underwent SBBI were retrospectively enrolled to design irradiation plans using tangential arc VMAT (taVMAT), half arc VMAT (haVMAT), and large arc VMAT (laVMAT). Dosimetric and delivery parameters of all designed plans were recorded and compared.

Results: Comparable target volume coverage was observed for all field arrangements. taVMAT significantly reduced the dose to spinal cord and the volume covered by 5 Gy (V) and V of the lungs while decreasing the conformity index of the target volume. It also increased the volume covered by 105% of the prescription dose (V) and V of the target volume. haVMAT considerably decreased V and V of the lungs, mean dose (D) and V of the heart and the liver. It also notably reduced D and V of the left anterior descending coronary artery while increasing the beam-on time. laVMAT significantly reduced the mean treatment time (range, 113-117 seconds) compared with the other field arrangements.

Conclusions: There were distinct differences in various dosimetric and delivery parameters for different field arrangements, highlighting the importance of selecting the appropriate field arrangement based on specific treatment goals and considerations. This study contributes valuable insights into the use of FFF-based VMAT techniques in SBBI.