Use of Low-dose Rate Irradiation to Measure the Intrinsic Radiosensitivity of Human T-lymphocytes

A comparison has been made of high (1·55 Gy min−1) and low dose-rate (0·0098 Gy min−1) irradiation in determining the intrinsic radiosensitivity of peripheral blood lymphocytes from normal individuals. Samples from 19 people were assessed using a limiting dilution assay and used to investigate the variability associated with evaluation of lymphocyte radiosensitivity after both high and low dose-rate irradiation. Repeat experiments on a single sample from one donor stored over a period of 6 months have been used to compare assay variability using the different dose-rates. Multiple samples taken from a single person over a period of 5 months were assayed at low dose-rate to assess intraindividual variation in measured in vitro radiosensitivity. At high dose-rate significant interexperimental variation in the measured parameters was demonstrated and, after allowing for this variability, no significant interindividual differences were found. At low dose-rate, sparing of cell kill was seen for all lymphocytes and led to an increase in the spread of data between individuals such that interindividual differences reached statistical significance for surviving fraction at 4 Gy, α (linear fit) and with p < 0·004 for all parameters.