关键词: 分次内CBCT, 体表引导放射治疗, 深吸气屏气技术, 乳腺癌

Abstract:

Background and purpose: In recent years, deep inspiration breath hold (DIBH) based on surface-guided radiation therapy (SGRT) has emerged as one of the most promising techniques in breast cancer radiotherapy. Conventionally, cone-beam CT (CBCT) is used before treatment to verify and correct patient positioning deviations. However, patient position may change during treatment, and pre-fraction CBCT cannot fully reflect real-time positional deviations. Therefore, this study aimed to introduce intra-fraction CBCT into left-sided breast DIBH radiotherapy to monitor and correct real-time deviations, verify whether patients achieve the desired position during treatment, and evaluate the clinical value of intra-fraction CBCT in left-breast radiotherapy. Methods: Clinical data from postoperative left-sided breast cancer patients treated at Fudan University Shanghai Cancer Center between June 2023 and January 2024 were collected. Patients with satisfactory cardiopulmonary function and stable DIBH compliance were included. Pre-fraction CBCT scans were performed before treatment, and data were recorded. During treatment, the gantry was rotated to -180° to trigger kV-level intra-fraction CBCT scanning. After gantry repositioning to the starting angle of the tangential field, MV beam delivery commenced. Intra-fraction CBCT scans were acquired for positional registration, and deviations were compared with pre-fraction CBCT results. Results: A total of 30 eligible patients were included, with 150 pairs of pre-fraction and intra-fraction CBCT images analyzed per patient. The mean registration deviations for intra-fraction CBCT were 26%, 52%, and 51% lower than pre-fraction CBCT in the X, Y, and Z axes, respectively (P<0.05), demonstrating significantly reduced real-time deviations. The probability of intra-fraction deviations being <6 mm was 100.0%, 100.0%, and 99.3% for the X, Y, and Z axes, respectively. Correlation analysis revealed a weak correlation between intra-fraction and pre-fraction deviations in the X-axis (P <0.05), while no significant correlation was observed for the Y and Z axes (P>0.05). Conclusion: Intra-fraction CBCT effectively monitors and corrects real-time positional deviations in left-sided breast DIBH radiotherapy, serving as a valuable supplement to conventional pre-fraction CBCT. It minimally impacts treatment efficiency while significantly improving positional accuracy, offering clinical and practical benefits for left-breast cancer radiotherapy.

Key words: Intra-fraction CBCT, Surface-guided radiation therapy, Deep inspiration breath hold, Breast cancer