To help physicians determine the exact location of the tumor, a headframe is attached to the patient's skull under local anesthesia. CT and MRI scans are taken, and doctors pinpoint the tumor on the scans and load the information into a computer. Working with a radiation oncologist and a neurosurgeon, a physicist calculates the angle, strength and duration of the radiation beam and figures out how to position it so it doesn't harm critical structures. He uses a computer program that gives him a three-dimensional picture of the tumor and its relation to other areas of the brain, based on the scans taken earlier. In simple cases, it takes about an hour to develop a treatment plan.
Complicated cases can take up to four hours.
Once treatment calculations are complete, the information is fed into a computer that controls a linear accelerator, which is adapted for radiosurgery. It takes another hour to set up the machine and double check settings for the table, the headframe and the accelerator. Finally, the patient's head is lowered into a guide on the treatment table, and the headframe is locked into place. Numbers are checked one last time, and the treatment begins. After preparations that can take up to seven hours, a walnut- sized tumor is irradiated in less than 20 minutes.