Strontium-90 Plesiotherapy uses a dime-sized radioactive probe to deliver low energy beta radiation therapy to superficial tumors of the skin, eyelids, and ears, many of which are difficult to remove surgically. Side effects are rare because the radiation only travels to a depth of about 4 mm, thus avoiding underlying structures. Some patients treated with Strontium-90 radiation therapy develop an ulceration which forms a scab and heals over time. These side effects rarely bother the patient. Treatment is usually completed in one or two 5-10 minute sessions.