Supplement antioxidant administration during radiotherapy in cancer, yes or no?

Radiotherapy is widely used for cancer treatment. In radiotherapy, free radicals and other reactive oxygen species are produced when they are passed through cells. These free radicals can interact with critical macromolecules such as DNA which is led to cell toxicity and death. Radioprotective agents and antioxidant supplements can scavenge free radicals and protect cells against toxicity induced by these toxic substances. Although free radicals produced by radiotherapy are necessary for cancer treatment, they are toxic for normal cells. It is a paradoxical effect for antioxidant as a protective agent in normal cells or tumor cells. It is the main problem of antioxidant co-administration in patients during radiotherapy. After reviewing clinical trials and systematic reviews about efficacy of antioxidants to reduce side effects induced by radiotherapy in patients, it was found that antioxidant supplements improved average survival rate and reduced side effects induced by radiotherapy. Further clinical trials for more evidence for selection of antioxidant, dosage and duration of administration are needed.