Efficacy and Tolerance of IMRT Boost Compared to IORT Boost in Early Breast Cancer: A German Monocenter Study

SIMPLE SUMMARY: The benefit of administering an extra dose to the tumor bed (boost) prior or simultaneously to adjuvant breast radiotherapy in terms of local recurrence rate has already been the subject of several studies and, thus, has already found justification in appropriate patient cases. In this study, we compared two boost techniques, an intraoperative radiotherapy (IORT) boost and an intensity-modulated radiotherapy boost (IMRT), analyzing two patient collectives to determine the equivalence of the two techniques or which of the two proves superior. According to our monocenter data on tumor control, survival rates, toxicities, and cosmetic results, no significant differences were revealed between the two boost techniques, and it cannot be generalized that one technique is more advantageous than the other. ABSTRACT: The aim of this retrospective study is to compare the two boost subgroups, IORT or IMRT, in terms of overall survival (OS), progression-free survival (PFS), cosmesis, and acute and late toxicity. It shall be shown whether and which of the boost techniques offers better results with respect to the facial points, since there are already many studies on applying boost to the tumor bed after/during breast conserving surgery, and there are few which compare the different techniques. For this comparison, two subgroups of 76 patients each (n = 152), treated between 2002 and 2015, were enrolled in the study. In one subgroup, the 9 Gy boost was intraoperatively administered after complete removal of the primary tumor, while the other subgroup received the boost of 8.4 Gy percutaneously and simultaneously integrated into the tumor bed after breast conserving surgery. Both subgroups have subsequently undergone whole breast irradiation (WBI) of 50.4/50 Gy in 1.8–2 Gy per fraction. OS and the incidence of late toxicity did not differ between the two subgroups and no risk factor was found regarding PFS. Acute toxicities initially occurred significantly less (p < 0.001) in the IORT subgroup; however, after WBI took place, this difference vanished. Therefore, boost application by means of IORT or IMRT can be considered equivalent.