Radiotherapy is a treatment that uses different types and sources of ionising radiation to control or cure some tumours, as well as other diseases, by damaging cells' DNA so that they loose the ability to divide or regenerate.

In a large majority of cases it is used in combination with other treatments, such as chemotherapy, immunotherapy or surgery.

Patients with blood diseases that require treatment with radiotherapy usually receive a type called external beam radiotherapy. In such cases the treatment is administered, in stages, by a machine that emits ionising radiation aimed at a particular area of the body. The patient must therefore attend every day for one or more sessions of radiotherapy during the course of the treatment. When radiotherapy is used to condition a patient before a transplant, the type used is usually whole body irradiation.

The damage caused to healthy cells by radiotherapy is what causes its side effects, which tend to be associated with the area that has been irradiated. The most usual are hair loss, changes to the skin and tiredness. Other side effects are more specific to the area affected, such as nausea, vomiting and diarrhoea, in the case of irradiation of the abdomen, and headache and inflammation of the parotid glands, in the case of the irradiation of the head.

The symptoms usually revert back over time, when the cells have regenerated. It is important to remember that some side effects can be permanent, such as, infertility in the case of the irradiation of the reproductive organs, or they may appear after a period of time (late side effects). It is therefore important to be informed specifically about the kind of treatment to be received.