Synchronous bilateral breast carcinoma irradiation: A comparative investigation between flattened and unflattened beams.

Synchronous bilateral breast carcinoma (SBBC) radiotherapy is a very complicated and time-consuming process. Considering the advantages of unflattened (FFF) beams at a high dose rate, this work investigated the feasibility of FFF beam application in SBBC radiotherapy and compared the advantages between FFF and flattened (FF) beams. CT images of 13 patients with SBBC were retrospectively collected to design intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans using FF and FFF beams. Dosimetric verification was applied for each plan. The target volume metrics, dose received by organs at risk (OARs), and delivery parameter of the plans were documented. All plans met the universal tolerance limits in dosimetric verification. FFF decreased the volume to receive 5 Gy (V5Gy), V7Gy, and mean dose of the left lung but slightly increased the V30Gy of the liver for VMAT and decreased the V17Gy and V20Gy of the right lung for IMRT. No remarkable differences between FF and FFF were found in the other investigated OARs and all the investigated target volume metrics. The mean treatment times of FFF were 66 and 45 s shorter than those of FF for IMRT and VMAT, respectively. FFF beams were feasible and had advantages in reducing treatment time and protecting the lung while maintaining the target volume metrics in SBBC irradiation.