Abstract: Objective To analyze the correlation between clinical characteristics and dosimetric factors for the patients receiving intensity⁃modulated radiotherapy after breast cancer surgery, and to provide reference for the formulation of postoperative radiotherapy plan. Methods The data of breast cancer patients who received postoperative radiotherapy in Tenth People's Hospital Affiliated to Tongji University from January 2020 to December 2021 were retrospectively analyzed. Clinical characteristics, ipsilateral lung volume (ILV), mean lung dose (MLD) and volumetric dosimetric parameters V5-V50 were collected to analyze the correlation with the radiation pneumonitis. Results 75 cases of 177 breast cancer patients developed radiation pneumonitis; among these cases, 93.3% were grade 1 and 6.7% were grade 2. Univariable analysis showed that double target therapy, internal mammary lymph node radiotherapy, MLD, V13, V15, V20, V25, V30, V35, V40, V45, and V50 were all associated with the occurrence of radiation pneumonitis (all P<0.05). Multivariable analysis showed that both V35 and V50 were independent risk factors for the occurrence of radiation pneumonitis (all P<0.05). The receiver operator characteristic curve showed that the sensitivity and specificity of predicting radiation pneumonitis with 20.27% of V35 as the cut⁃off value were 42.7% and 77.5%, respectively, with an AUC of 0.619. The sensitivity and specificity of predicting radiation pneumonitis with 3.155% of V50 as the cut⁃off value were 50.7% and 75.5%, respectively, with an AUC of 0.626. Conclusions Both V35 and V50 are independent risk factors for the occurrence of radiation pneumonitis, and minimizing the high⁃dose region V35 and V50 are of great significance in reducing the incidence of radiation pneumonitis.

Key words: Breast cancer, Radiation pneumonitis, Intensity modulated radiotherapy, Clinical characteristic, Dosimetric parameters