Survival rates immediately following complicated cancer surgery or radiotherapy are two to three times higher at facilities that perform a high volume of these procedures. Cancer patients needing such treatments therefore should be served in more-experienced settings, says the National Cancer Policy Board of the Institute of Medicine and National Research Council in its report Ensuring Quality Cancer Care. There are 80 NCI-designated cancer centers across the U.S. There are a number of radiation treatments for therapy (Stereotatic, Gamma-Knife and Brachyradiation to name a few). These are "focal", not "diffuse". Radiation therapy may be used as a primary treatment option for inoperable tumors. Radiation therapy can cause cerebral edema, which can cause ICP and neurological symptoms. External radiation to a tumor bed with a 2 cm border may be an option. This involves therapy once a day for about six weeks and allows radiation to 6000 rads. This begins as soon as the surgical incision has healed if administered post-surgically (for cancerous tumors only). Post-irradiation cerebral necrosis can occur 6 to 36 months after treatment is completed, with symptoms similar to tumor recurrence. An MRI, CT, or PET can determine if the symptoms are indicating tumor recurrence or necrosis. If cerebral necrosis is identified, it can be treated with surgical removal of the necrotic tissue and steroids (clinical trails with hyperbaric oxygen therapy have been successful at Duke University).