Time-effect relationship of chromosome aberrations in peripheral lymphocytes after radiation therapy for seminoma.

The time-effect relationship of dicentrics and cells containing unstable chromosome abnormalities (Cu cells) was studied in peripheral lymphocytes of 40 blood samples from 23 patients suffering from seminoma during a time period of 0-1720 days after radiation therapy. Nine patients were studied before treatment. Since the half-time for the disappearance of damaged cells from circulating blood is an increasing function of post-exposure time it can only be expressed as a differential value. The present model discriminates between the mean lifetime m for lymphocytes and a parameter q which is the differential half-time for the decline of damaged cells immediately after exposure (t = 0). If the time t is short compared with m the decline is asymptotically time-hyperbolic rather than exponential and can be described by q only. According to recalculations of previous data, comprising 30 years post exposure, m approximates 10 years. Differential half-times can be derived for any time post treatment within the analysed time period for the decline of the incidence of dicentrics. For example at the end of therapy (t = 0) the differential half-time was calculated to be 0.4 years and at 1720 days post exposure 3.6 years resulted. The corresponding values for the percentage of Cu cells cannot be derived for t = 0; at 1720 days 3.9 years resulted.