Hypofractionated whole-breast radiation therapy with simultaneous integrated boost after breast-conserving surgery: preliminary real-life experience of the Radiation Therapy Oncology Group 1005 trial

Abstract Objectives This study aimed to report cosmetic and oncological outcomes for patients who underwent adjuvant hypofractionated whole-breast radiation therapy (WBRT) (40 Gy in 15 fractions) with simultaneous integrated boost (SIB) (48 Gy) using IMRT (intensity modulated radiation therapy) or VMAT (volumetric modulated arc therapy) after breast-conserving surgery at our institution as per the experimental arm of the Radiation Therapy Oncology Group (RTOG) 1005 trial. Methods One hundred and seventy patients who underwent adjuvant moderate hypofractionated WBRT with SIB after breast-conserving surgery were identified between 29 July 2019 and 22 September 2024. Results The median age was 57 (range: 33-84). The pTstage distribution was as follows: Tis: 18.2%, T0: 9.4%, T1: 57.1%, T2: 14.1% and T3: 1.2%. pN0: 82.9% and pN1mic: 17.1%. Neoadjuvant/adjuvant chemotherapy and adjuvant endocrine therapy were administered in 17.6%, 26.5% and 58.2% of cases, respectively. IMRT and VMAT techniques were used in 79.4% and 20.6% of cases, respectively. The median mean heart dose was 0.9 Gy (0.2-4.7). The median V16 and V8 of the ipsilateral lung were 12.8% (0-60.5) and 19.1% (0-63), respectively. Grade 1 and grade 2 radiodermitis and oedema were reported in 58.8%, 4.7%, 3.5%, and 0.6% of cases, respectively. With a median follow-up of 14 months (0-55), the 1-year local relapse-free survival, the locoregional relapse-free survival, the metastases recurrence-free survival, and overall survival were all 100%. Conclusions Our preliminary data suggest that routine use of SIB with WBRT using IMRT or VMAT was feasible with a favourable risk-benefit ratio. Longer follow-up can confirm the safety of this approach. Advances in knowledge Preliminary data from our department showed that combining whole-breast irradiation with SIB and IMRT or VMAT was feasible for early-stage breast cancer.