目的  前瞻性观察乳腺癌改良根治术后患者胸壁发生放射性皮炎（RD）的情况，分析与RD发生有关的危险因素。方法  对786例Ⅱ～Ⅲ期女性乳腺癌改良根治术后患者进行前瞻性队列分析，自放疗开始每周对患者胸壁皮肤情况进行观察评估。第一观察终点为放疗开始后90 d，第二观察终点为CTCAE v4.03中定义的1～3级RD症状。结果  从放疗开始后90 d内RD累积发生率为30.2%（n=237），其中184例患者的RD发生在放疗期间，53例发生在放疗结束后。多因素分析显示：糖尿病史、肥胖、使用补偿膜与RD的发生相关。结论  糖尿病史、肥胖与皮肤补偿膜的使用均为乳腺癌改良根治术后放疗胸壁RD的相关危险因素，尤其是糖尿病史与皮肤补偿膜的使用，与2～3级RD的发生有显著相关性。在确定放疗方案前对相关风险因素进行评估并认真考虑补偿膜的使用指证有助于降低乳腺癌改良根治术后胸壁放疗患者发生RD的风险。

Objective  To prospectively observe the incidence of radiation dermatitis (RD) on the chest wall of patients underwent postmastectomy radiotherapy (PMRT) and analyze risk factors relevant to the incidence of RD. Methods  The prospective cohort analysis was performed for 786 female patients with stage Ⅱ-Ⅲ breast cancer who underwent PMRT. The skin of chest wall was observed and assessed weekly from the beginning of PMRT. The primary endpoint was 90 days after PMRT and the secondary endpoint was the incidence of Grade 1-3 RD symptoms defined by CTCAE v4.03. Results  The accumulative incidence of RD within 90 d after PMRT was 30.2% (n=237) and 184 of them developed RD during PMRT and 53 of them developed RD after PMRT. Multivariate analysis indicated that diabetes, obesity, and the use of skin bolus were correlated with the incidence of RD. Conclusion   Diabetes, obesity, and the use of skin bolus are risk factors of RD on the chest wall of patients underwent PMRT. Especially diabetes and the use of skin bolus significantly correlate with the incidence of grade 2-3 RD. Evaluation of relevant risk factors and carefully considering about the use of skin bolus before determining the radiotherapy plan are helpful for reducing the risk of developing RD of patients underwent PMRT.