HUMAN PLASMA ANTIOXIDANT CAPACITY DURING RADIOTHERAPY FOR LUNG-CANCER- A CLINICAL-STUDY

Even though it is well established that oxygen-free radicals are the m ain mechanism responsible for the cytotoxicity produced during radioth erapy, the role of the human antioxidant defense system in clinical ra diation oncology is still to be clarified. Changes in the human plasma total peroxyl radical trapping capacity (TRAP) and its individual com ponents were followed during clinical radiotherapy for lung cancer. Si xteen patients receiving radical-aimed radiotherapy provided blood sam ples nine times during the treatment. Our hypothesis was that oxygen-f ree radical production increased by irradiation should decrease the pl asma TRAP as a consequence of oxidative stress. Only a moderate reduct ion 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 unident ified components were clearly different in those patients showing comp lete or partial response to the treatment and those in which the disea se progressed unabated. Plasma ascorbate levels showed no significant changes during radiotherapy. A decrease in vitamin E concentrations wa s 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 anti oxidants (UNID).