Simplified quantitative estimation in vitro of lymphocyte radiosensitivity applied to patients with chronic lymphocytic leukaemia

Lymphocyte survival changes observed at 1, 2 and 3 days as responses to 3 doses of ionising radiation in vitro (40, 100, and 500 cGy) are analysed by computer according to a simple (single cell population) mathematical model. Intrinsic radiosensitivity, the susceptibility to lethal injury, which is expressed as the D 37 value (the radiation dose permitting 37% survival), is estimated separately from the kinetics of subsequent death of lethally-irradiated cells (expressed as their half-life, or t 1 2 value). Among the 35 patients with B-cell CLL studied (15 were never treated), both parameters varied widely and independently of one another, t 1 2 ranged from 9–200 h and above, D 37 from 14–500 cGy or above. Twenty-three patients were deemed ‘radiosensitive’ ( D 37 below 110 cGy). D 37 level did not correlate with treatment status, mode of treatment, clinical staging (Rai) or lymphocyte count. With some exceptions, D 37 remained relatively constant for individual patients with increasing duration of disease or alterations in treatment status. The assay method may prove useful as an aid in predicting response to low-dose splenic irradiation (SI) in CLL.