Radiotherapy improves survival of patients who underwent breast-conserving surgery. Tumour bed boost further improves the local control that can be delivered by interstitial brachytherapy, electron beam or X-ray photon beam therapy (external beam radiotherapy). The aim of the study was to compare cosmetic outcome and the factors affecting it after interstitial brachytherapy or external beam radiotherapy.

Sixty patients with infiltrating ductal carcinoma who underwent breast conserving surgery were prospectively enrolled and treated by electron or X-ray photon beams to a total dose of 40 Gy delivered in 15 fractions followed by tumour bed boost by interstitial brachytherapy ( n = 30) or external beam radiotherapy ( n = 30) to a dose of 14 Gy delivered in four fractions. Both the groups were compared in terms of cosmesis, acute toxicity, late toxicity, dosimetry and survival.

Median follow up period of the cohort was 56 months (range: 50–63 months). There was no significant difference in the two groups in terms of toxicity and cosmetic outcome. Excellent/good cosmesis was seen in 85 % of total patients. Late skin toxicity was significantly lower in the group receiving interstitial brachytherapy. Doses to the normal structures such as heart and skin were significantly lower in patients who had brachytherapy. Using univariate analysis, tumour location (central region), use of neoadjuvant chemotherapy, vertical nipple deviation of more than 2 cm and grade 3 skin induration were found to be significantly associated with fair/poor cosmetic outcome.

Tumour bed boost by external beam radiotherapy or interstitial brachytherapy provide equivalent result in terms of cosmesis. Interstitial brachytherapy has an edge over external beam radiotherapy in reducing skin doses resulting in decreased incidence of higher grade of late skin toxicity.