Early breast cancer is defined as tumours not more than five centimetres in diameter, with either impalpable or palpable but not fixed lymph nodes and with no evidence of distant metastases.1 Primary treatment of early breast cancer usually involves surgery to remove the tumour (breast conserving surgery or mastectomy) and management of the axilla.1 Complete pathology reporting following surgery will inform the adjuvant treatment options for individual women.
Several trials have shown that breast conserving surgery followed by whole breast radiotherapy is effective in reducing the risk of local recurrence and improving the long-term outcomes of appropriately selected patients with early breast cancer.2
Conventional adjuvant whole breast radiotherapy is typically delivered over a period of 5 weeks using a standard dose of 2 Gray (Gy) per treatment episode (fraction) in 25 fractions to a total dose of 50 Gy.3 A tumour bed boost of 10-16 Gy in 2 Gy fractions4,5 is sometimes delivered after whole breast radiotherapy.
Hypofractionated whole breast radiotherapy involves fewer fractions; however each fraction contains a larger daily dose of radiation than the conventional 2 Gy per fraction. The total dose of radiation used in a course of hypofractionated radiotherapy is reduced to compensate for the increased toxicity effect of larger daily fractions.
Compared to conventional radiotherapy regimens, the duration of a hypofractionated radiation treatment course is shorter by several days or weeks, as fewer fractions are required. A hypofractionated regimen may be more convenient for patients and less-resource intensive than a conventionally fractionated regimen.6
Conventional radiotherapy and hypofractionated radiotherapy can be hypothesised to have a similar effect, based on radiobiological principles. The aim of hypofractionated radiotherapy is to balance as high a daily dose as possible in order to kill tumour cells, against a dose low enough to minimise the side-effects of treatment.
Sensitivity of tissues to radiation fraction size is described by the α/β ratio. Low α/β values indicate greater sensitivity to fraction size than higher α/β values. It has been hypothesised that breast cancer is as sensitive to fraction size as normal breast tissue with a low α/β value, and confirmation would indicate that fewer, larger fractions are as effective as conventional 2 Gy fractions.7