Liu, Yen-TingYen-TingLiuChu, Kuan-AnKuan-AnChuHuang, Shih-TingShih-TingHuangShen, Chia-WeiChia-WeiShenLiou, Jia-HungJia-HungLiouHSIANG-KUANG LIANGSUNG-HSIN KUO2025-11-042025-11-042025-10-08https://scholars.lib.ntu.edu.tw/handle/123456789/733373Background: We examined the acute toxicity of hypofractionated breast radiotherapy (HFRT) with hybrid techniques combining field-in-field intensity-modulated RT (FIF-IMRT) to the whole breast (WB) with inverse-IMRT for concomitant boost (CB) to the tumor bed. Methods: This prospective exploratory study enrolled patients with early-stage breast cancer (EBC) or breast ductal carcinoma in situ (DCIS) from January 2020 after breast-conserving surgery. All patients consistently received a 16-fraction hybrid 40 Gy FIF-IMRT plans for WB, CB 8 Gy inverse-IMRT to the tumor bed (hybrid-CB group). Identical contours and planning target volume coverage were replanned with conventional tangential FIF-IMRT for WB (50 Gy in 25 fractions), followed by electron beams to the tumor bed (10 Gy in 5 fractions) (sequential group). Results: We enrolled 25 patients with EBC and 9 with breast DCIS; 2 (5.9 %) patients had grade 2 acute radiation dermatitis, and 5 (14.7 %) patients had grade 1 skin fibrosis. No recurrence was observed during the median follow-up of 44 months. Mean homogeneity index in the hybrid-CB and sequential groups were 8.9 and 18.6, respectively (p < 0.01). Considering left-sided disease, we found no significant differences in mean, maximal dose, and V5 of heart between groups (p = 0.09, 0.80, and 0.06). V20 values of the ipsilateral lung dose were 13.0 % and 12.9 % (p = 0.47) in the hybrid-CB and sequential groups, respectively, while normal tissue complication probability parameters for breast fibrosis were 20.02 % and 22.13 %, respectively (p < 0.01). Conclusion: HFRT combined with FIF-IMRT for WB with inverse-IMRT CB to the tumor bed causes rare acute radiation dermatitis and decreases moderate-to-severe breast fibrosis without compromising disease control.enBreast fibrosisConcomitant boost (CB)Hypofractionated breast radiotherapy (HFRT)Intensity-modulated radiation therapy (IMRT)NTCP modelTumor bed[SDGs]SDG3journal article10.1016/j.jfma.2025.09.03741067952