Placing the Boost in Breast-conservation Radiotherapy: A Review of the Role, Indications and Techniques for Breast-boost Radiotherapy

Randomised trials have established that the addition of a boost dose of radiotherapy to the lumpectomy site after whole-breast adjuvant radiotherapy further improves local control achieved by whole-breast radiotherapy alone. The absolute size of this benefit varies according to the baseline risk of local recurrence. Age is the strongest predictor of benefit. Below the age of 40 years, the absolute benefit of a boost seems to be substantial, and there are no clearly identified groups unlikely to benefit. Above the age of 50 years, the benefit is small, and several additional risk factors for local failure would need to be present to merit boost treatment. These may include tumour size, high grade, high mitotic rate, lymphovascular invasion, extensive and high grade associated with intraduct carcinoma, receptor-positive tumours when avoidance of anti-oestrogen therapy is desired or receptor-negative tumours. Other independent reasonable indications for the use of a boost would be positive margins where further surgery is not indicated. If a boost is indicated, a variety of techniques may be used and toxicity and cosmetic results remain highly acceptable. Overall, there seems to be no substantial differences in boost technique results; however, interstitial techniques may have advantages for deeper targets compared with electrons. Irrespective of technique, accurate localisation will maximise the benefit of a boost. Surgical clips are strongly recommended to facilitate localisation.