Radiation therapy involves using high-energy x-rays to shrink tumors and destroy cancer cells. This treatment may be delivered as a focused beam that is projected into the body (called external therapy) or in the form of radioactive materials placed at the site of the cancer through thin plastic tubes (called brachytherapy).

Radiation therapy is used often as follow-up (adjuvant) treatment to destroy cancer cells that remain in the body after a radical or partial nephrectomy.
It also may be used as palliative therapy to lessen pain or bleeding in patients with inoperable or widespread metastatic RCC. In such cases, there is no expectation of cure; the object is simply to ease the patient's discomfort.

Radiation therapy alone has a relatively low success rate in treating RCC, and often produces unpleasant side effects:

• Diarrhea
• Fatigue
• Headaches and cognitive problems (if treating metastatic cancer of the brain)
• Lung and respiratory problems (if treating cancer that has spread to the lungs or bones in the chest)
• Nausea
• Skin irritations