Skin reaction as a biological parameter for prospective studies of different dose schedules with the CRE formula.

The validity of the CRE formula for prospective calculation of biologically equivalent radiation doses with different fractionation schedules has been investigated. Patients with breast cancer were irradiated postoperatively on bilateral parasternal fields. The biological radiation effect was studied by reflectance spectrophotometry of skin erythema and pigmentation. The results from daily irradiation in comparison with twice-a-week, once-a-week, 3-times-a-day and "split-course" irradiation indicate that the formula is a very good predictor of the acute skin erythema and pigmentation.