PERIPHERAL-BLOOD LYMPHOCYTE DECREASE AND MICRONUCLEUS YIELDS DURING RADIOTHERAPY

Purpose: To investigate the relationship between lymphocyte decrease a nd cytogenetic response in individual patients undergoing radiotherapy . Materials and methods: Peripheral blood lymphocytes obtained from 35 patients with pelvic and from 14-with head and neck tumours before an d during radiotherapy were PHA-stimulated in vitro and the cultures pr epared for the cytokinesis-block micronucleus test. For some patients only, the micronucleus test was carried out after 2 Gy in vitro X-irra diation, and 3-aminobenzamide (2 mM) was used to calculate the SAB-ind ex. Results: The initially observed individual Variation in the decrea se of lymphocytes disappeared with increasing number of radiation expo sures, reaching a stable level at about 500/mu l lymphocytes in the bl ood. The slope of the relationship between the reciprocal of the lymph ocyte decrease ratio and equivalent dose indicates the radiosensitivit y of the lymphocyte pool in individual patients. The micronucleus test performed on lymphocytes obtained from patients during radiotherapy ( in vivo) provided a lower cytogenetic response than the in vitro micro nucleus yield for the same dose, so it was possible to calculate the c ytogenetic recovery factor k. A correlation was found between the 3AB- index calculated before radiotherapy, and the recovery factor k. Concl usions: The SAB-index, the micronucleus frequency after 2 Gy in vitro X-irradiation, and the cytogenetic recovery factor are proposed as pre dictive of individual response to radiotherapy.