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

Purpose: This study aimed to report cosmetic and oncological outcomes for patients who underwent adjuvant hypofractionated whole-breast radiation therapy (WBRT) (40Gy in 15 fractions) with simultaneous integrated boost (SIB) (48Gy) 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 RTOG 1005 trial.

Materials and methods: 170 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 0.9Gy (0,2-4,7). The median V16 and V8 of the ipsilateral lung were 12.8% (0-60.5) and 19.1% (0-63). Grade 1 and grade 2 radiodermitis and edema 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 one-year local relapse free survival (LRFS), the locoregional relapse free survival (LRRFS), the metastases recurrence free survival (MRFS) and overall survival were all 100%.

Conclusion: Our preliminary data suggests that routine use of SIB with WBRT using IMRT or VMAT was feasible with a favorable risk-benefit ratio. Longer follow-up can confirm the safety of this approach.