BASAL-CELL DENSITY IN HUMAN SKIN FOR VARIOUS FRACTIONATION SCHEDULES IN RADIOTHERAPY

Changes in the epidermal basal cell density (BCD) in human skin were d etermined during and immediately after fractionated radiotherapy, The basal cells are one of the target cell types responsible for acute ski n reactions and measuring the BCD is a histological method for studyin g the time course and degree of reaction. Thirty-two patients with bre ast cancer participated in this study. They received postmastectomy ra diotherapy to the thoracic wall. A 3-mm punch biopsy was taken from th e irradiation field once a week for 6-10 weeks and the linear basal ce ll density was determined. Standard fractionation at two different dos e levels (40 and 50 Gy) as well as hypofractionation and accelerated t reatment have been investigated. For the first 3 weeks we found a cons tant decline in the BCD (about 0.8%/day), independent of dose and frac tionation schedule. Using the nadir value as endpoint we found a dose- response relationship between 40 and 50 Gy, and for total effect (TE)- values in the range 430-1015. Compared to standard fractionation, hypo fractionation showed somewhat less effect and accelerated fractionatio n showed significantly less effect. The reduced effect of accelerated fractionation is interpreted as a result of lack of cell cycle redistr ibution of cells between the two daily fractions in this type of tissu e, The removal rate of dead or doomed cells could also affect the resu lts for schedules with different overall time, The results of BCD were also compared to erythema. We found a good correlation between both t hese endpoints of acute skin reactions in comparison of different frac tionation schedules.