Radiation sensitivity of lymphocytes from healthy individuals and cancer patients as measured by the comet assay

Lymphocytes of healthy volunteers (n=24) and of tumour patients (n=30, 18 o f whom had experienced severe side-effects) were irradiated with x-rays in vitro. DNA damage was analysed after 0.25-2 Gy and DNA repair after 2 Gy, a nd quantification of both endpoints was done by the comet assay. The indivi dual differences in radiation-induced DNA damage as well as in the repair k inetics were observed to be striking for both healthy donors and tumour pat ients. After a repair time of 3 h. following 2 Gy x-irradiation, some of th e healthy volunteers showed no residual DNA damage at all in their lymphocy tes, whereas others revealed about 30%. There was no indication that our re sults were affected by either age, gender or smoking habits. Slow repair ki netics and high amounts of residual damage were characteristic for many but not all tumour patients who had experienced severe side-effects in their n ormal tissues during or after radiotherapy (n=18). Our conclusion is that t hose individuals showing poor DNA repair characteristics in the lymphocytes following in vitro irradiation, have a high probability of being radiosens itive. The opposite conclusion is not necessarily true: if repair is effect ive, this does not mean that the individual is radioresistant, because fact ors other than impaired repair may cause radiosensitivity.