1.    There is compelling research for the use AND avoidance of supplemental antioxidants during radiation. Antioxidants are free radical scavengers. Free radicals are thought to damage the cell walls and promote the development of abnormal or cancerous cells. Antioxidants bind with the free radicals so that they cannot damage the cells.  The research that supports the use of antioxidants says that they protect the healthy cells and lessen side effects of treatment. The research that opposes the use of antioxidants says that it protects the cancer cells and diminishes the efficacy of the treatment. Lawenda BD, Kelly KM, Ladas EJ, Sagar SM, Vickers A, Blumberg JB. Should Supplemental Antioxidant Administration Be Avoided During Chemotherapy and Radiation Therapy? J Natl Cancer Inst, 2008; 100:773-783

I also want to make a distinction between taking a nutrient like antioxidants (Vitamins A (precoursor beta carotene), E, C and selenium) for nutritional use and taking it to work as a drug within the body.

There is not enough research completed to support the use of any particular antioxidant supplement or amount. This is to say using it pharmacologically (as a medication rather than a nutrient).

Eating a diet that includes good sources of antioxidants as part of a balanced diet is thought to be of benefit in overall health before, during and after treatment. Sources of antioxidants such as citrus, berries, dark green vegetables, sweet potatoes is encouraged in the 5-9 servings per day.