Response of human organs to single (or fractionated equivalent) doses of irradiation

Characteristics of the kinetics of radiation response of human tissues and organs are exemplified by effects in the testis and the ovary. Also, published dose-incidence curves for specified levels of injury in bone marrow, liver, bladder and lung are characterised in terms of single doses as well as single-dose equivalents calculated from fractionated doses using the alpha/beta equation. It is shown that these curves, analysed using a Poisson model, have slopes characterised by D0-equivalents ranging between 1.25 and 2.5 Gy. These values are higher or within the range of values reported in general for single-dose survival curves of human cells in primary culture (range of D0 values 0.7-1.8 Gy). This indicates that single-cell responses together with other complicating biological and statistical sources of heterogeneity under discussion, could form a basis for explaining the steepness of dose-incidence curves for organ injury after fractionated doses. With local organ irradiation, increase in the single-dose equivalent by 3-10 per cent would increase the complication rate from 5 per cent to 10 per cent. Higher dosage increases (by up to two times) apply to fractionated doses.