The two main types of radiation type are ionizing and nonionizing.
The ionizing would be the radiotherapy and non-iodizing is from the sun.
Ionizing = free radical formation
non ionizing (UVB) = DNA damage by formation of pyrimidine dimers
Radiation causes damage by generating hydroxyl free radicals (Pathoma chapter 3 table). Therefore, if something minimizes the damage of radiation, it has to inhibit free radical formation.
therapeutic ionizing radiation(gamma rays,x-rays);
-DNA double-strand breakage
-Free radical formation