ESTRO meets Asia 2024 - Abstract Book

S398

RTT – Treatment planning, OAR and target definitions

ESTRO meets Asia 2024

Purpose/Objective:

Tumor bed boost during whole-breast irradiation (WBI) was proved to improve the local control, while it is unknow whether simultaneous integrated boost (SIB) or sequential boost (SeB) is preferable. This study aimed to compare the safety and efficacy of SIB and SEB during hypofractionated whole-breast radiotherapy after breast-conserving surgery.

Material/Methods:

Retrospectively reviewed 775 patients treated with SIB between 2016 and 2018 and 357 patients treated with SeB between 2010 and 2015. The prescribed dose was 43.5 Gy in 15 fractions to whole breast and simultaneously 49.5 Gy in 15 fractions (SIB) or sequentially 8.7 Gy in 3 fractions (SeB) to tumor bed. Toxicities were evaluated according to Common Toxicity Criteria for Adverse Events v3.0. Breast cosmetic evaluation based on Havard system. Local control (LC), locoregional control (LRC), disease-free survival (DFS), overall survival (OS) and breast cancer-specific survival (BCS) were calculated by Kaplan-Meier method. The impact of SIB and SeB on survival outcomes was assessed by inverse probability of treatment weighting (IPTW) by adjusting for age, body mass index, TNM stage, histological grade, lymphovascular invasion (LVI), molecular subtype, administration of chemotherapy, chemotherapy cycles, endocrine therapy and anti-HER2 targeted therapy. Survival rates before or after weighting were compared with the log rank test. Chi-square test was preformed to compare the characteristics and grade 2 or higher toxicities between groups. Median follow-up was 66 months. Patients with SIB have more T2-3 stage, N1-3 stage, ductal carcinoma in situ, LVI than patients with SeB. Regional nodal was irradiated in 123 (15.9%) patients with SIB and 11 (3.1%) patients with SeB. Intensity-modulated radiotherapy was used in 100% of patients with SIB and 100% WBI and 5.9% SeB, the remaining 94.1% of patients with SeB were irradiated with electrons. Grade 2 or higher skin toxicity, pneumonitis, breast swelling, pain, induration, lymphedema and shoulder mobility were comparable between groups. The rates of fair or poor cosmetic result in SIB was lower than that in SeB (2.5% vs 10.4%, p<0.001). The 5-year LC, LRC, DFS, OS and BCS rates of SIB and SeB were 97.8% vs 98.8% (p = 0.1), 97.7% vs 97.1% (p = 0.7), 94.1% vs 93.1% (p = 0.7), 97.4% vs 97.7% (p = 0.5) and 98.2% vs 98.3% (p = 0.9), respectively. After IPTW, there is no significant difference between SIB and SeB in 5-year LC (97.6% vs 95.7%, p = 0.4), LRC (97.5% vs 94.3%, p = 0.2), DFS (94.0% vs 92.0%, p = 0.7), OS (97.4% vs 98.5%, p = 0.5) and BCS (98.1% vs 98.7%, p = 0.7). Results:

Conclusion:

In contrast to SeB, SIB is alternative approach since it improved breast cosmetic with comparable toxicities profile and survival outcomes but shorten treatment. Further follow-up is needed to assess long-term outcomes.

Keywords: Simultaneous integrated boost; sequential boost

280

Proffered Paper

discussions on splenic dose-volume constraints: a clinical perspective

Yifu Ma, Yuehong Kong, Meiling Xu, Junjun Zhang, Pengfei Xing, Jianjun Qian, Liyuan Zhang