Question: How does radiation therapy work? I thought it immediately killed the tumor, but I have heard that isn't always true.

Answer: Radiation therapy does not usually work immediately in any patient with any type of pituitary tumor. Pituitary tumor cells are fairly slow growing and the aim of radiation is to destroy the cells when they are dividing. Depending on the type of tumor, radiation therapy may take many years to be effective. In Cushing's Disease, the results of conventional (fractionated) radiation were reported in the New England Journal of Medicine. In 30 patients treated with conventional radiation, 25 achieved normal hormone levels within 18 to 114 months. At the University of Virginia, we have treated patients with a focused method of radiation delivery, the Gamma Knife. We have treated approximately 60 Cushing's patient's and have adequate follow-up information in 38. Of the 38, 24 have achieved normal 24-hour urine cortisol levels after treatment. The average time to becoming normal was 13 months with a range of 2 to 48 months. There are no published results using another method of focused radiation, the Lineac. Because radiation is not immediately effective, it is usually reserved for treatment of patients who have not been cured with surgery.