Session Item

Accelerated partial breast irradiation using interstitial brachytherapy has been evaluated in huge number of Phase 2 trials and in three Phase 3 randomized trials. The Groupe Europeen de Curietherapie of European Society for Radiotherapy and Oncology (GEC-ESTRO) published a randomized Phase 3 non-inferiority trial in 2015. The trial randomized 1184 patient with low risk invasive ductal and ductal carcinoma in situ after breast conserving therapy to either whole breast irradiation (WBI) or accelerated partial breast irradiation (APBI) using the multi-catheter interstitial technique. At 6.6-year follow-up, APBI was not inferior with a cumulative incidence of 5y.-cumulative local recurrence rate of 1.44% for APBI vs. 0.92% for WBI. In addition, the risk of late side effects, overall survival, and disease-free survival were not found to be significantly different between arms. Polgar et al. (Budapest trial) published already a 10-year update of a prospective clinical trial randomizing 258 patients between partial breast irradiation (PBI) and whole breast irradiation (WBI). The primary end point was local recurrence , and the secondary end points were overall, cancer-specific, and disease-free survival. With a median follow-up of 10.2 years, the actuarial LR was 5.9% in the WBI arm and 5.1% in the APBI arm. There was no significant difference in the secondary end points between the two arms. Excellent to good cosmetic outcomes were statistically significantly superior in the PBI arm at 81% compared with 63% in the WBI arm. Subsequent to these trials a third prospective randomized Phase 3 trial - NSABP B-39/RTOG 0413 trial - was performed. This trial differed from the prior trials as it was an equivalence trial, enrolled patients from age 18 and included more high-risk subgroups. A total of 4216 patients were enrolled and randomized between WBI or APBI using either external beam 3D conformal therapy (71% pts.), a single entry brachytherapy catheter (23.3% pts.) or  interstitial brachytherapy (5.7%). The primary outcome was ipsilateral LR as a first recurrence and a secondary outcome of survival. At a median follow-up of 10.2 years, the cumulative incidence of ipsilateral breast tumor recurrence was 4.6% in the APBI arm vs. 3.9% in the WBI arm. The absolute difference was 1% at 10 years but fell just short of the equivalence criteria. There was no difference in survival end points, and the toxicities were similar. Notably, this study was not designed to test for differences in outcomes from the various APBI techniques and as consequence particularly for ABPI with interstitial brachytherapy it´s not possible to give any statement.

In summary based on current available published data of large number Phase 2 and phase 3 trials it´s evident that APBI with brachytherapy is a proven treatment method for selected breast cancer patients with robust Level 1 evidence.