A prospective clinical trial of post-operative radiotherapy delivered in three fractions per week versus two fractions per week in breast carcinoma.

The results are presented of a five-year prospective trial of 411 patients with breast carcinoma treated by mastectomy and post-operative radiotherapy. Twice or thrice weekly dose-fractionation techniques were used, i.e. 12 fractions in 28 days and six fractions in 18 days. The results show that, in terms of survival and control of local disease, the two techniques are very similar. The early and late radiation effects on the normal tissues up to five years are similar and acceptable. Dose levels thought to be biologically equivalent on the basis of experience at St Thomas's Hosiptal were selected. It is stressed that there is a narrower margin of normal tissue tolerance when six fractions over 18 days are used, that it is essential to treat all fields on each treatment occasion and that the total maximum tissue dose of 3600 R is not exceeded. Attention is drawn to the fact that the dose for six fractions, derived from the NSD formula which would be predicted to be equivalent to the 12-fraction dose is, in fact, over 10% higher than the dose used here and likely to produce unacceptable late radiation changes.