Radiation is the use of forms of energy rays, such as x-rays and gamma rays, to kill cancer cells. While radiation therapy affects both normal and cancer cells, because cancer cells do not repair themselves as well as normal cells, they should die or shrink after treatment.

Radiation therapy is usually reserved for high-risk or advanced cases of melanoma where surgery is not possible or may be complicated. It is rarely used to treat primary melanoma, except in cases where patients are not good candidates for surgery or refuse surgical treatment.

The main role of radiation therapy is to relieve symptoms of melanoma that has metastasized to areas such as the brain or bone. Although it cannot cure advanced melanoma, it can frequently shrink tumors that cause discomfort. In the case of brain metastases, it is the primary treatment, with the goal being to relieve symptoms such as partial paralysis, headaches and seizures.

Although still considered an "unproven treatment," radiation may be targeted to the regional lymph node basin to prevent tumor recurrence after surgery.