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Radiotherapy (also called radiation therapy) is a cancer treatment that uses high doses of radiation, (usually X-rays), to kill cancer cells and shrink tumors. Radiation therapy kills cancer cells or slows their growth by damaging their DNA.

Radiation therapy can be given with the intent to cure the cancer, but it may also be used to reduce the relapse risk (i.e., the risk that the cancer comes back). In addition to this, radiotherapy can help to relieve symptoms. For example, radiotherapy to the bone is often used in multiple myeloma patients to alleviate bone pain.

In the past, radiation was delivered to larger areas of the body, including regions that were not immediately affected by the malignancy. This caused damage to surrounding, healthy tissues or organs and increased the risk for the development of new (secondary) cancers. More recently, however, modern radiotherapy techniques have been developed that allow a targeted delivery of radiotherapy. The most popular of these techniques in the context of hematological malignancies is called involved-field radiotherapy (IFRT). With IFRT it is possible to only deliver radiation to the areas of the body that are affected by the malignancy. For example, if a lymphoma affects lymph nodes on the left side of the neck, IFRT will selectively deliver radiation to the entire left side of the neck. In contrast, if the lymphoma affects two areas like the neck and the armpits, radiation will be delivered to these two sites only. Another targeted radiation technique consists of conformal radiotherapy. With this technique, radiation is given from multiple angles to closely fit a 3D image of the tumor mass, which was created using CT images. Another advanced technique in radiotherapy, with less toxicity consists of involved node or involved site radiotherapy (ISRT) in which only the lymph nodes that are active on a PET-CT scan are irradiated.

On the other end of the radiotherapy spectrum, we can find total body irradiation (TBI), in which radiation is given to the entire body. This technique can be used to suppress a patient’s immune system in preparation of a donor (allogenic) stem cell transplantation.

Radiotherapy can cause certain side effects. These include include a sore skin (which may change color), a general feeling of fatigue, nausea, diarrhea, a loss of appetite and hair loss in the area that is being treated. Importantly, most of these side effects can be treated or prevented, and most will go away after the treatment is stopped. However, there is a limit to the amount of radiation an area of the body can safely receive over the course of a lifetime. Depending on how much radiation an area has already received, patients may not be able to have radiation therapy to that area a second time.

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