High doses of radiation are used to target and destroy cancer cells. To help ensure that all the cancer is destroyed, doctors deliver radiation with a margin (an area of healthy cells), surrounding the cancer area. This is to ensure that no abnormal cells are missed.
During and after treatment, the radiation damages both cancerous and healthy cells. The cancerous cells are not able to repair themselves and heal, while the healthy cells can typically heal. This is the reason for treating in several fractions (small doses over several days), which gives healthy cells a chance to recover. The cells recovering is what often causes fatigue — the most common side effect of radiation therapy.
Each organ in the body or type of tissue can withstand certain amounts of doses of radiation. When radiation is delivered to different areas of the body, different side effects will occur. Some side effects are short-term, while others are longer-term. Some side effects are enhanced or made worse by concurrent chemotherapy treatments.
Side effects are most common within, or due to changes within, the treatment area (including the margin) that received radiation.
Early side effects happen during or shortly after treatment. These side effects tend to be short-term, mild, and treatable. They’re usually gone within a few weeks after treatment ends. The most common early side effects are fatigue (feeling tired) and skin changes. Other early side effects are usually related to the area being treated, such as hair loss and mouth problems (that can include inflammation of the gums, taste changes, dry mouth, and pain).
Late side effects can take months or even years to develop. They can occur in any normal tissue in the body that has received radiation. The risk of late side effects depends on the area treated, as well as the radiation dose that was used. Careful treatment planning can help avoid serious long-term side effects. It’s always best to talk to your radiation oncologist about the risk of long-term side effects.