Techniques of tumour bed boost irradiation in breast conserving therapy: current evidence and suggested guidelines

Breast conservation surgery followed by external beam radiotherapy to breast has become the standard of care in management of early carcinoma breast. A boost to the tumour bed after whole breast radiotherapy is employed in view of the pattern of tumour bed recurrences in the index quadrant and was particularly considered in patients with some adverse histopathological characteristics such as positive margins, extensive intraductal carcinoma (EIC), lymphovascular invasion dose in patients even without such factors and for all age groups. The maximum absolute reduction of local recurrences by the addition of boost is especially seen in young premenopausal patients. At the same time, the addition of boost is associated with increased risk of worsening of cosmesis and no clear cut survival advantage. Radiological modalities such as fluoroscopy, ultrasound and CT scan have aided in accurate delineation of tumour bed with increasing efficacy. A widespread application of these techniques might ultimately translate into improved local control with minimal cosmetic deficit. The present article discusses the role of radiotherapy boost and the means to delineate and deliver the same, identify the high risk group, optimal technique and the doses and fractionations to be used. It also discusses the extent of adverse cosmetic outcome after boost delivery, means to minimise it and relevance of tumour bed in present day scenario of advanced radiotherapy delivery techniques like Intensity modulated radiation therapy (IMRT).