[Radiosensitizing effect of hyperfractionated radiation]

To determine whether hyperfractionated treatment has benefits in the radiation therapy, two melanoma cell lines were irradiated with eight 0.5 Gy fractions as well as one single 4 Gy in vitro. The radiation was performed in air and in hypoxia as well. Cells were also irradiated in the presence of dibromodulcitol, a bifunctional alkylating agent with a weak radiosensitizer effect. The aim of the study was to examine whether hyperfractionation can influence the radiosensitizing effect of the bioreductive agent. Survival of the cells was determined immediately and 24 hours after various treatments by cell counting in hemocytometer and clonogenic assay. The number of the apoptotic cells was determined by the TUNEL assay and was followed up to 72 hours after treatment. Hypoxic cells had higher sensitivity than normoxic cells after 0.5 Gy irradiation. Radiosensitizing enhancement of DBD was higher with fractionated irradiation. The number of the apoptotic cells was significantly higher after hyperfractionated treatments than after single dose treatment combinations. Our results showed the significance of the hyperfractionated irradiation with 0.5 Gy per fraction in vitro.