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

Abstract Background: This paper studied retrospectively the dosimetry and therapeutic accuracy of deep inspiration breath hold (DIBH) radiotherapy in regional nodal radiation (RNI)-containing right-sided breast cancer patients who had completed treatment based on surface guided radiotherapy (SGRT) technology, hoping to clarify the clinical application value and related issues . Methods: Free breath (FB) and DIBH plans were prepared for31 RNI-containing right breast cancer patients who had completed DIBH radiotherapy based on SGRT technology. Four organs at risk (OARs) including heart, right coronary artery (RCA), right lung and liver were made dosimetriccomparison on the premise that the planning target volume was met dose-volume prescription requirements. Meanwhile, 31 patients were divided into edge of 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 lung volume increment of the right side were compared among the three groups. Results: All planning target volume met the dose-volume coverage criteria. Compared with FB, DIBH slumpedthe maximum dose of heart and RCA by 44.3% and 46.7% respectively. The mean dose was went down by 12.5% for right lung. The mean liver dosedecreased the most, with an average reduction rate of 69.4%. The setup error of EXP group in the anterior-posterior (AP) direction was 3.6±4.5mm, significantly higher than the other two groups (2.2±2.6mm, 2.4±3.1mm). The rightlung volume increment in EXP, SM and LBW groups was 72.3%, 69.9 % and 67.2%, respectively(P=0.08), and the corresponding breath-holding heights were 13.5±3.7mm, 10.3±2.4mm, and 9.6±2.8mm, respectively(p<0.05). Conclusions: SGRT-based DIBH can better protect the heart, RCA, ipsilateral lung and liver of right breast cancer patients combined with RNI. Different respiratory gating primary points have different therapeutic accuracy and breath-hold height. On the premise of reasonable respiratory gating primary points, interfractions can be widely applied as it has high repeatability and breath-holding stability to ensure therapeutic accuracy.