Radiation Therapy (or 'Radiotherapy') is a very effective way of destroying some types of cancer cell using only small amounts of radiation. In the treatment of breast cancer radiotherapy is used primarily to destroy any cancer cells remaining in and around the healthy breast tissue after surgery. Radiation therapy can reduce the chance of cancer coming back by around 70%.
Where it is used radio therapy is highly targeted to the area where there may still be cancer cells present, so its side effects are generally localised and do not affect other parts of the body. Radiotherapy treatment can also be used in the armpit/lower neck area after lymph nodes have been removed for the same reason and occasionally as an extra precaution if lymph nodes have not been removed at all.
Radiotherapy is often used after a course of chemotherapy has finished, or after surgery where chemotherapy will not be used.