The Gamma Knife is a radiosurgical device used to treat certain conditions of the brain that require more accuracy than conventional radiosurgery (using linear accelerators or other methods) can provide. It was developed by Lars Leksell in the 1950's with the first treatment occuring in 1958. Since then it has been used to treat over 70,000 patients with brain tumors and vascular malformations in the brain.

So how does it work? Simple! Well, kind of... Before the procedure begins, a complete MRI or CT scan of the patient must be done. Doctors then can use the results of this to pinpoint the exact location and size of the tumor, and begin to plan the procedure. The Gamma Knife itself is a rather large container which holds cobalt 60, a radioactive isotope of cobalt. It uses radiation from the cobalt to fire 201 beams of radiation into the patient's brain. To do this, first the patients head must be fixed to a frame of reference, should the head move at all during the procedure, normal brain tissue may be damaged. A lightweight frame is screwed into the patient's skull (under local anesthetic) which served as a locking mechanism to fix the patient's head into position.

Next, the patient is placed on the movable bed on the gamma knife. The frame is locked to the supports on either side of the patient's head, and a large collander is fitted over top of their head. The collander has 201 holes in it to allow radiation to be directed toward the tumor, the diameter of the collander and the size of the holes are chosen based on the size of the tumor and the dosage needed for treatment. Basically what this does is allow radiation in from a hemispherical area around the patient's head. Each beam of radiation is not strong enouh to damage normal tissue. The head is positioned so that all of the beams will intersect at the tumor, thus while the surrounding tissue does not recieve any strong radiation, the tumor itself recieves a very concentrated dose of radiation. This, combined with the fact that tumors are more easily damaged by radiation than healthy tissue, allows the tumor to be destroyed without significant damage to surrounding tissue.

The prodecure generally takes 15-45 minutes to complete. Several treatments may be necessary depending on the nature of the tumor, however most patients are released from the hospital within 24 hours of the procedure. The advantage of the Gamma Knife is that there is very little damage to surrounding tissue and no invasive procedures are performed (unlike conventional surgery), and it has a greater accuracy than more conventional radiosurgery (.2 mm tolerance vs 2 mm tolerance on a linear accelerator unit). Common complications include local swelling and headaches, while more rare side effects include nausea and seizures.

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