Human plasma antioxidant capacity during radiotherapy for lung cancer: a clinical study.

Even though it is well established that oxygen-free radicals are the main mechanism responsible for the cytotoxicity produced during radiotherapy, the role of the human antioxidant defense system in clinical radiation oncology is still to be clarified. Changes in the human plasma total peroxyl radical trapping capacity (TRAP) and its individual components were followed during clinical radiotherapy for lung cancer. Sixteen patients receiving radical-aimed radiotherapy provided blood samples nine times during the treatment. Our hypothesis was that oxygen-free radical production increased by irradiation should decrease the plasma TRAP as a consequence of oxidative stress. Only a moderate reduction of the plasma TRAP was found during the therapy in the study group taken as a whole, but the development pattern of TRAP and its unidentified components were clearly different in those patients showing complete or partial response to the treatment and those in which the disease progressed unabated. Plasma ascorbate levels showed no significant changes during radiotherapy. A decrease in vitamin E concentrations was seen after 6 Gy (p=0.05). Uric acid concentrations increased towards the end of the radiotherapy in both response groups (p=0.02 at 50 Gy). In this study, 26.6% of the plasma TRAP was due to unidentified antioxidants (UNID).