When the risk of surgery is high because of other medical problems, or where the patient simply refuses surgery, the “gamma knife” procedure may be used. This is a method of irradiating the tumor, invented by Lars Leksell in 1971. This procedure avoids surgery with its risks. In the past, this option was usually recommended only for higher risk surgical cases because of the possibilities of late radiation complications, and the need for ongoing MRI monitoring of the results of the procedure. Today Gamma Knife has come a long way, and can be used when surgery is not an option.