Five-year results of a prospective trial of IORT-photon boost and hypofractionated whole-breast irradiation after breast-conserving surgery.

Aim: To assess for the first time the safety and feasibility of combining photon-IntraOperative RadioTherapy (ph-IORT) with hypofractionated whole-breast irradiation (hWBI) in patients referred to adjuvant radiotherapy after Breast-Conserving Surgery (BCS).

Methods: From February 2019 to August 2020, patients referred for breast-conserving surgery (BCS) in our institution were prospectively included in the present trial. BCS was discussed in the multidisciplinary tumor board (MTB). 20 Gy were prescribed to the surface of the applicator of an Intrabeam^®ph-IORT during BCS. hWBI (40.5 Gy/2.67 Gy/15frx) was planned to be administered 3-5w after BCS. All patients were treated by hWBI VMAT-Rapid-Arc&Daily Exac-Trac-IGRT. Systemic adjuvant treatment was indicated following international guidelines. The aim of this study was to assess for the first time the local control, cancer-specific survival, and overall survival rates of BC patients treated by combined photon-IORT-boost and hWBI after BCS. Secondary endpoints include the long-term toxicity and cosmetic outcomes observed in these patients.

Results: Fifty-seven patients were included in the trial. No ≥ G3 late toxicity was observed at 12 months of follow-up and thereafter. After a median follow-up of 61 months (range 54-66 months), all patients were free of local or regional relapse. Two patients had a second tumor in the contralateral breast. One triple-negative patient developed lung metastases 3 years after her initial diagnosis. Cause specific and overall survival were 100% at 5 years.

Conclusion: We demonstrated for the first time that ph-IORT + hWBI is effective and safe in the long-term for patients referred to adjuvant RT after BCS.