SGRT‐based DIBH radiotherapy practice for right‐sided breast cancer combined with RNI: A retrospective study on dosimetry and setup accuracy

BACKGROUND: We retrospectively studied the dosimetry and setup accuracy of deep inspiration breath‐hold (DIBH) radiotherapy in right‐sided breast cancer patients with regional nodal irradiation (RNI) who had completed treatment based on surface‐guided radiotherapy (SGRT) technology by Sentinel/Catalyst system, aiming to clarify the clinical application value and related issues. METHODS: Dosimetric indicators of four organs at risk (OARs), namely the heart, right coronary artery (RCA), right lung, and liver, were compared on the premise that the planning target volume met dose‐volume prescription requirements. Meanwhile, the patients were divided into the edge of the xiphoid process (EXP), sternum middle (SM), and left breast wall (LBW) groups according to different positions of respiratory gating primary points. The CBCT setup error data of the three groups were contrasted for the treatment accuracy study, and the effects of different gating window heights on the right lung volume increases were compared among the three groups. RESULTS: Compared with free breath (FB), DIBH reduced the maximum dose of heart and RCA by 739.3 ± 571.2 cGy and 509.8 ± 403.8 cGy, respectively (p < 0.05). The liver changed the most in terms of the mean dose (916.9 ± 318.9 cGy to 281.2 ± 150.3 cGy, p < 0.05). The setup error of the EXP group in the anterior‐posterior (AP) direction was 3.6 ± 4.5 mm, which is the highest among the three groups. The right lung volume increases in the EXP, SM, and LBW groups were 72.3%, 69.9%, and 67.2%, respectively (p = 0.08), and the corresponding breath‐holding heights were 13.5 ± 3.7 mm, 10.3 ± 2.4 mm, and 9.6 ± 2.8 mm, respectively (p < 0.05). CONCLUSIONS: SGRT‐based DIBH radiotherapy can better protect the four OARs of right‐sided breast cancer patients with RNI. Different respiratory gating primary points have different setup accuracy and breath‐hold height.