Radiation therapy is a cancer treatment that uses high energy x-rays or other types of radiation to kill cancer cells. There are two types of radiation therapy.
External radiation therapy uses a machine outside the body to send radiation towards the cancer.
Internal radiation therapy uses a radioactive substance sealed in needles, seeds, wires or catheters that are placed directly into or near the cancer.
Radiation therapy for testicular cancer is delivered by a carefully focused beam of radiation from a machine outside the body. This is known as external beam radiation. The treatment is much like getting an x-ray, but the radiation is more intense. The procedure itself is painless. Before your treatments start, the medical team will take careful measurements to determine the correct angles for aiming the radiation beams and the proper dose of radiation. Each treatment lasts only a few minutes, but the setup time -- getting you into place for treatment -- usually takes longer.
In general, radiotherapy is mainly used for patients with seminoma, which is very sensitive to radiation. It does not seem to work well for non-seminomas. Sometimes it is used after orchiectomy (the operation to remove the testicle) and is directed at the lymph nodes at the back of the abdomen (the retroperitoneal lymph nodes). This is to kill any tiny bits of cancer in those lymph nodes that can't be seen. Radiotherapy can also be used to treat small amounts of seminoma that are known to have spread to the nodes (based on changes seen on CT scans).
(sources: cancer.gov & cancer.org )