Abstract
OBJECTIVE: To investigate the optimal radiotherapy regimen for synchronous bilateral breast cancer (SBBC) by utilizing dosimetric and radiobiological indicators, and to assess the impact of applying an optical surface monitoring system(OSMS) on the precision of SBBC radiotherapy treatment. METHODS: Nine patients with SBBC who underwent breast-conserving radiotherapy were retrospectively selected. Four treatment plans were designed for each patient using the Versa HD (Elekta, Stockholm) accelerator: single-isocenter intensity-modulated radiotherapy/volumetric modulated arc therapy(IMRT-ISO1/VMAT-ISO1) and dual-isocenter IMRT/VMAT(IMRT-ISO2/VMAT-ISO2), with a prescription dose of 42.4 Gy in 16 fractions. Dosimetric parameters and radiobiological impact were measured for the target and organs at risk(OARs). The monitoring log files of three SBBC patients were analyzed to quantitatively assess real-time delta shifts encompassing six degrees of freedom (DOFs) during intrafraction and interfraction treatment processes. RESULTS: Compared to both the IMRT techniques, the VMAT techniques offered superior target conformity, uniformity, and dose fall-off capability. Among the four treatment plans, VMAT-ISO1 exhibited optimal performance by significantly reducing radiation exposure volume to OARs while maintaining exceptional precision in dose delivery and execution efficiency. The tumor control probability (TCP) was exceeded by 98.5% for all four modalities. According to the OSMS logs, the maximum absolute error in translational motion during the treatment of three SBBC patients was predominantly manifested along the vertical(VRT) axis, with an mean value of 2.2 mm. Additionally, it was observed that the coronal plane (YAW) exhibited the largest error in terms of rotational angle, with an mean deviation of 1.1°. CONCLUSIONS: The VMAT-ISO1 technique demonstrates apparent dosimetric and radiobiological advantages in SBBC radiotherapy, ensuring precise dose delivery and shortening treatment durations. The accuracy of SBBC radiotherapy is ensured by OSMS through pre-treatment positioning correction and real-time monitoring throughout the treatment process.