Comparison of simultaneous integrated tumor bed boost and sequential boost during hypofractionated whole-breast irradiation after breast-conserving surgery.

This study aimed to compare the safety and efficacy of simultaneous integrated boost (SIB) and sequential boost (SeB) during hypofractionated WBI. 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. 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. 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.