Likewise, radiation to the head or neck region may cause a sore throat, but it won't result in nausea or diarrhea. Normal cells are able to repair DNA damage far better after small doses of radiation than after large doses. In fact, experience with many thousands of patients treated over many decades has shown us that we can minimize side effects by dividing a large total dose of radiation into many smaller daily doses delivered over several weeks rather than giving a few massive doses in several days. This results in fewer side effects. Although it seems very inconvenient to give treatment over such a long period of time, this is the only way to deliver enough total radiation to permanently destroy your cancer without also permanently hurting normal tissues.
Some patients undergoing radiation therapy feel fatigue during treatment.
There are different reasons for this fatigue depending upon the part of the body being irradiated. If the treatment field includes significant portions of the bone marrow, a patient might experience a reduction in blood count sufficient to cause fatigue. This reduction in blood count along with the fatigue it causes are temporary. Even without radiation of the bone marrow, some patients feel a minor fatigue with radiation treatment. The exact cause of this fatigue is uncertain but probably results from the expenditure of metabolic energy used by normal tissue in the repair of radiation induced damage.