As the last time I went to see Dr Adler with a friend's son t I was helping gather information/options for treatment of a benign brain tumor was 15 years ago I went on radiologyinfo.org a site cofounded by the Radiological Society of No American and the American College of Radiologists and got the following:
How does the equipment work?
The Gamma Knife® utilizes a technique called stereotactic radiosurgery, which uses multiple beams of radiation converging in three dimensions to focus precisely on a small volume, such as a tumor, permitting intense doses of radiation to be delivered to that volume safely. Current models of the Gamma Knife® use advanced robotic technology to move the patient in submillimeter increments during treatment, to focus radiation successfully on all parts of the target. In most cases, Gamma Knife® treatments are given in a single session.
Under local anesthesia, a special rigid head frame incorporating a three-dimensional coordinate system is attached to the patient's skull with four screws. Imaging studies, such as magnetic resonance imaging (MRI), computed tomography (CT), or angiography, are then obtained and the results are sent to the Gamma Knife®'s planning computer system. Together, physicians (radiation oncologists and neurosurgeons) and medical physicists delineate targets and normal anatomical structures. They use a planning computer program to determine the exact spatial relationship between the target, normal structures and the head frame to calculate Gamma Knife® treatment parameters. Targets often are best treated during the treatment session with combinations of several successive aimings, commonly known as "shots." The physicians and physicists routinely consider numerous fine-tuning adjustments of treatment parameters until an optimal plan and dose are determined.
Using the three-dimensional coordinates determined in the planning process, the frame is then precisely attached to the Gamma Knife® unit to guarantee that when the unit is activated, the target is placed exactly in the center of approximately 200 precision-aimed, converging beams of (Cobalt-60 generated) gamma radiation. Treatment takes anywhere from several minutes to a few hours to complete depending on the shape and size of the target, the number of "shots" and the dose required. Patients do not feel the radiation. Following treatment the head frame is removed and the patient may return to normal activity.
As I understand it he only way to attach something to the skull so there is no "wiggle room" eg for broken necks and after neck surgeries is for the teeth of the screw to enter through the outer table of the bone. I cannot imagine they don't need ti minimize :wiggle room" at least as much if not more for accurate aiming into the brain.
The pin holes are very shallow(there is little between the skin and the scalp in those positions, even if as kids we were called "fat heads!", but never the less it seems to require local anaesthetic if one is awake.
When done for broken necks and neck surgery the screws remain in longer, either for the duration of the surgery (hours) or until the fracture/surgery heals. In those cases the bumps where the screws were can remain slightly raised thereafter, possibly causing discomfort to those who wear headbands near the area.--that is usually the case when only two screws are used due to the screw placement positions.
All four screws should be behind the hairline so any residual bumpiness or tenderness should be known only to the person themselves (or their hairdresser!) I haven't heard of any complaints, but as I mostly read the literature and go to conferences, I am not likely to.
In the big picture of things, I would think any annoyance at the time this is done or after would be minimal (needing to postpone washing hair after the procedure, etc)
Haven't read any complaints on this site about post gamma knife scalp problems. Anyone?
Addendum--looks like they have been working on altering how the screws used:
Neurosurgery. 2007 Apr;60(4 Suppl 2):339-43; discussion 343-4.
Angled screw holes for anterior posts and a frame-positioning device for gamma knife radiosurgery: allowing for better targeting of intracranial lesions.
Quiñones-Hinojosa A, McDermott MW.
Source
Department of Neurological Surgery, Johns Hopkins University, Baltimore, Maryland 21231, USA.
aquinon2@jhmi.edu
Abstract
OBJECTIVE:
Gamma knife radiosurgery requires frame positioning so that the treatment target is as close to the center of the frame and as low as possible to cover all of the posterior fossa contents. In this study, we report the use of two devices developed by the senior author (MWM) that facilitate these two crucial objectives in the treatment of intracranial targets using the gamma knife.
METHODS:
Custom front posts with threaded screw holes drilled at 5-, 10-, and 15-degree angles were created by the manufacturer at our request. A U-shaped metal device for frame positioning was designed in-house and fits into the holes at the 100-mm mark on the lateral sides of the Leksell stereotactic frame base. This allowed the positioning device to snap securely into the frame for use in positioning. The positioning device was constructed so that the lowest possible frame position would be achieved with each frame application, while avoiding collisions with the magnetic resonance imaging localizer box.
RESULTS:
Angled front posts allowed for pin contacts with the cranium anterior and/or superior to the superior temporal line despite a lateral or posterior position of the frame. This avoided penetration of the temporalis muscle and reduced discomfort for patients. The U-shaped metal device was used in place of the Velcro straps or ear bars routinely used for frame positioning in which the distance from the frame base to the top of the head must always be measured to avoid collisions with the localizer box. During the past 2 years, these devices have been used on a daily basis, achieving the desired results. In many cases, their use has avoided the need for frame repositioning and rescanning for targets that cannot be reached because of inexact frame positioning.
CONCLUSION:
A new design with angled screw holes in the front posts used for gamma knife radiosurgery allows surgeons to avoid penetration of the temporalis muscle and to maintain a perpendicular orientation of the fixation screw to the outer table of the cranium. They may also prevent mechanical creep caused by the obliquity of pin contact with the cranium and resulting loss of torque. We also present a simple device that may be useful in frame positioning. The device ensures a frame position as low as possible without the need for measurement at the time of frame positioning.
PMID:
17415172