Comparison of intraoperative radiotherapy as a boost vs. simultaneously integrated boosts after breast-conserving therapy for breast cancer

Raluca Stoian; Jan-Philipp Harald Exner; Mark Gainey; Thalia Erbes; Eleni Gkika; Ilinca Popp; Simon K B Spohn; David Krug; Ingolf Juhasz-Böss; Anca-Ligia Grosu; Tanja Sprave

doi:10.3389/fonc.2023.1210879

Comparison of intraoperative radiotherapy as a boost vs. simultaneously integrated boosts after breast-conserving therapy for breast cancer

Front Oncol. 2023 Jun 20:13:1210879. doi: 10.3389/fonc.2023.1210879. eCollection 2023.

Authors

Raluca Stoian^{1

2

3}, Jan-Philipp Harald Exner^{1

2

3}, Mark Gainey^{1

2

3}, Thalia Erbes^{3

4}, Eleni Gkika^{1

2

3}, Ilinca Popp^{1

2

3}, Simon K B Spohn^{1

2

3}, David Krug⁵, Ingolf Juhasz-Böss^{3

4}, Anca-Ligia Grosu^{1

2

3}, Tanja Sprave^{1

2

3}

Affiliations

¹ Department of Radiation Oncology, University Hospital of Freiburg, Robert-Koch-Strasse, Freiburg, Germany.
² German Cancer Consortium (DKTK) Partner Site Freiburg, German Cancer Research Center (dkfz), Neuenheimer Feld, Heidelberg, Germany.
³ Faculty of Medicine, University of Freiburg, Freiburg, Germany.
⁴ Department of Obstetrics and Gynecology, Medical Center, University of Freiburg, Freiburg, Germany.
⁵ Department of Radiation Oncology, University Hospital Schleswig-Holstein, Arnold-Heller-Str., Kiel, Germany.

Abstract

Background: Currently, there are no data from randomized trials on the use of intraoperative radiotherapy (IORT) as a tumor bed boost in women at high risk of local recurrence. The aim of this retrospective analysis was to compare the toxicity and oncological outcome of IORT or simultaneous integrated boost (SIB) with conventional external beam radiotherapy (WBI) after breast conserving surgery (BCS).

Methods: Between 2009 and 2019, patients were treated with a single dose of 20 Gy IORT with 50 kV photons, followed by WBI 50 Gy in 25 or 40.05 in 15 fractions or WBI 50 Gy with SIB up to 58.80-61.60 Gy in 25-28 fractions. Toxicity was compared after propensity score matching. Overall survival (OS) and progression-free survival (PFS) were calculated using the Kaplan-Meier method.

Results: A 1:1 propensity-score matching resulted in an IORT + WBI and SIB + WBI cohort of 60 patients, respectively. The median follow-up for IORT + WBI was 43.5 vs. 32 months in the SIB + WBI cohort. Most women had a pT1c tumor: IORT group 33 (55%) vs. 31 (51.7%) SIB group (p = 0.972). The luminal-B immunophenotype was most frequently diagnosed in the IORT group 43 (71.6%) vs. 35 (58.3%) in the SIB group (p = 0.283). The most reported acute adverse event in both groups was radiodermatitis. In the IORT cohort, radiodermatitis was grade 1: 23 (38.3%), grade 2: 26 (43.3%), and grade 3: 6 (10%) vs. SIB cohort grade 1: 3 (5.1%), grade 2: 21 (35%), and grade 3: 7 (11.6%) without a meaningful difference (p = 0.309). Fatigue occurred more frequently in the IORT group (grade 1: 21.7% vs. 6.7%; p = 0.041). In addition, intramammary lymphedema grade 1 occurred significantly more often in the IORT group (11.7% vs. 1.7%; p = 0.026). Both groups showed comparable late toxicity. The 3- and 5-year local control (LC) rates were each 98% in the SIB group vs. 98% and 93% in the IORT group (LS: log rank p = 0.717).

Conclusion: Tumor bed boost using IORT and SIB techniques after BCS shows excellent local control and comparable late toxicity, while IORT application exhibits a moderate increase in acute toxicity. These data should be validated by the expected publication of the prospective randomized TARGIT-B study.

Keywords: SIB; adjuvant; breast cancer; intraoperative radiotherapy (IORT); radiotherapy; toxicity.