A comparison of a brachytherapy and an external beam radiotherapy boost in breast-conserving therapy for breast cancer: local and any recurrences.

PURPOSE: Adding a tumour bed boost to whole-breast irradiation in breast-conserving therapy reduces local recurrence rates. The purpose of the present study was to investigate whether the boost technique influences the magnitude of the effect.

METHODS: Patients treated with breast-conserving therapy for invasive breast cancer between 2000 and 2007 were included in the analysis. Three groups were considered according to the applied boost technique: electrons, brachytherapy or photons. The endpoints were local recurrence and any recurrence. Cox regression models were used and correction for the confounders in the association between boost technique and outcome was performed using multivariable models.

RESULTS: 1879 tumours were included in the analysis. 1448 tumours (77.1%) were treated with an electron boost, 334 (17.8%) with a brachytherapy boost and 97 (5.2%) with a photon boost. Median follow-up was 13.1 years. The 10-year local recurrence rate was 2.2%. In multivariable analysis with correction for age, pathological Tumour or Node stage (pT, pN), chemotherapy and hormonal therapy, there was no significant difference between the three groups for the local recurrence risk (p = 0.89). 10-year any recurrence rate was 10.8%. In multivariable analysis with correction for age, pT, pN, resection margins, radiotherapy, year of diagnosis, chemotherapy and hormonal therapy, there was no significant difference between the brachytherapy group and the electron group or the photon group (p = 0.11 and p = 0.28, respectively). The photon group had more recurrences compared to the electron group (Hazard Ratio 1.81, 95% Confidence Interval 1.12; 2.92, p = 0.02).

CONCLUSIONS: The local recurrence risk reduction of the tumour bed boost in breast-conserving therapy is not influenced by the applied boost technique.