Background and purpose: This study aimed to compare the safety and efficacy of simultaneous integrated boost (SIB) and sequential boost (SeB) during hypofractionated WBI.
Materials and methods: This study analyzed data from two prospective studies, including 1,132 patients with pT1-3 N0-3 M0 breast cancer, of whom 775 received SIB and 357 received SeB. The prescribed dose was 43.5 Gy in 15 fractions to whole breast and/or nodal region, with either 49.5 Gy in 15 fractions (SIB) or 8.7 Gy in 3 fractions (SeB) delivered to tumor bed. Outcomes analyzed included survival outcomes, treatment-related toxicities, and cosmetic outcomes.
Results: The 5-year outcomes were local control rates of 97.8 % vs. 98.8 % (p = 0.12), locoregional control rates of 97.7 % vs. 97.1 % (p = 0.72), disease-free survival of 94.1 % vs. 93.1 % (p = 0.71), overall survival of 97.4 % vs. 97.1 % (p = 0.88), and breast-specific survival of 98.2 % vs. 97.5 % (p = 0.43) for SIB versus SeB, respectively. After stabilized inverse probability of treatment weighting, differences between groups remained non-significant. Rates of fair or poor cosmetic outcomes before and after radiotherapy were lower in the SIB group, but there was no difference in cosmetic deterioration (9.8 % vs. 7.6 %, p = 0.22). Grade 2 or higher toxicities, including skin toxicity, pneumonitis, breast swelling, pain, induration, lymphedema, and shoulder mobility issues, were comparable between groups.
Conclusion: SIB is a viable alternative to SeB, offering comparable toxicity profiles and survival outcomes while shortening treatment duration. Longer follow-up is warranted to assess long-term outcomes.
Keywords: Breast cancer; Hypofractionated whole-breast irradiation; Sequential tumor bed boost; Simultaneous integrated tumor bed boost.
© 2025 The Authors. Published by Elsevier B.V. on behalf of European Society for Radiotherapy and Oncology.