How Leksell Gamma Knife® Works

Rocky Mountain Gamma Knife Scanning Procedure

The Gamma Knife®consists of a large, heavily shielded hemisphere containing cobalt-60 sources. The collimated beams of radiation emanating from the cobalt-60 sources are positioned to converge on a single point within the unit, where the procedure takes place.

The patient is fitted with a stereotactic frame, which prevents movement of the head during treatment and provides a simple stereotactic approach. With the frame in place, precise coordinate settings are calculated to determine the exact location of the target. The patient rests on a special couch that moves into Gamma Knife®, positioning the patient’s head for treatment.

The procedure takes 15-40 minutes and is normally performed with local anesthesia.

The Gamma Knife® surgery delivers a single, high dose of ionizing radiation. At the point where all the beams simultaneously intersect, it delivers enough radiation to treat tumors or vascular malformations while minimizing dose to surrounding tissue.

A variety of collimator sizes allow for different beam sizes. Complex lesion shapes can be treated through multiple exposures and by readjusting the collimator and head position.

Patients experience virtually no discomfort or immediate side effects. The benefits of treatment manifest themselves over time; the lesion will dissolve or shrink gradually and eventually disappear, or will exhibit no further growth. The time period varies with the type, size, and location of the lesion.

Gamma Knife® surgery is more cost efficient than conventional neurosurgery. Patient hospital stays are short; patients are usually admitted the evening before treatment and discharged within a day of treatment. Gamma Knife® provides a clear socioeconomic advantage to the community.

Many of the expenses of disability and convalescence associated with conventional surgery are avoided. Gamma Knife®surgery fulfills an unmet need of its patient population by making it possible to treat formerly untreatable lesions and by making one-day brain surgery a reality.

Gamma Knife® — History of the Technique

Neurosurgeon Lars Leksell and biophysicist Börje Larsson developed the technique called stereotactic radiosurgery in the 1950s at the Karolinska Institute in Stockholm, Sweden.
Years of research produced an instrument that enabled surgeons to precisely target brain abnormalities with radiation beams. This instrument, Gamma Knife®, proved capable of destroying tumors, vascular malformations, and a limited number of functional disorder targets, (e.g. trigeminal nerve).

The first Gamma Knife®, installed in Stockholm in 1968, assisted in the treatment of hundreds of patients with brain tumors, arteriovenous malformations, acoustic tumors, meningiomas, pituitary adenomas, craniopharyngiomas and other brain tumors.

Gamma Knife® has been refined and improved over the years with advances in engineering radiation physics, and treatment planning. These changes have been incorporated into the Gamma Knife® program at Rocky Mountain Gamma Knife Center, which is one of approximately 275 prominent neurosurgical institutions in the world utilizing this high-tech neurosurgical tool.

Swedish neurosurgeon Lars Leksell – the creator of the Gamma Knife – defined Stereotactic Radiosurgery as the “delivery of a single high dose of radiation to a small and critically located intracranial volume without opening of the skull”.

With this technique, there is minimal risk of surgical complications, such as infection or hemorrhage, and it usually requires significantly shorter hospitalization than conventional open craniotomy.

Application of this state-of-the-art technique involves the use of a unique device –Leksell Gamma Knife®, which delivers intersecting beams of radiation to a specified target. Dose fall-off at the periphery of the target is such that the absorbed dose of surrounding tissue is minimal.

Gamma Knife® is a primary alternative to conventional neurosurgery and radiation therapy for arteriovenous malformations (AVM’s), as well as benign and malignant tumors. Gamma Knife® procedure is non-invasive and it can be especially useful for those patients who are not suitable for standard surgical techniques due to illness or advanced age. In many cases, Gamma Knife® is the only feasible treatment modality. Additionally, Gamma Knife® is a potent adjunct to surgery for recurrent and partially resected tumors, to endovascular embolization for large AVM’s, and to radiation therapy for malignant tumors.

Evolution of Leksell Gamma Knife®

Gamma Knife® was developed by Professor Lars Leksell of the Karolinska Institute in Stockholm, Sweden, together with biophysicist Professor Börje Larsson of the Gustaf Werner Institute, University of Uppsala.

In 1949 Professor Leksell created the Leksell Micro-Stereotactic System®, which permitted the mechanical placement of a needle, cannula or electrode at precise locations within the brain without direct visual guidance.

Professor Leksell recognized the need for a tool to allow for treatment of deep-seated intracranial structures without opening of the skull and the hazards of open surgery. He was convinced that agents other than cannulas or electrodes could be used to eradicate pathologies or to create therapeutic lesions in functional disorders.

In 1951, externally applied X-rays were substituted for the instruments used in the open stereotactic procedures. By coupling a source of radiation with a stereotactic guiding device, the first radiosurgical procedure was thus performed. Leksell found that by administering a single dose of radiation, it was possible to successfully destroy deep brain structures. He called this technique “stereotactic radiosurgery”.

During the 1950s and 1960s, Professor Leksell conducted intensive research in order to identify the ideal radiation source and equipment for stereotactic radiosurgery. Linear accelerators (photons) and synchrocylotrons (protons) were tried and evaluated. However, none proved to be satisfactory in terms of accuracy, reliability, simplicity, patient safety, expense or maneuverability. A set of criteria for radiosurgical equipment was formulated and Gamma Knife® was developed in response to these needs.

The first stereotactic Gamma Knife® using cobalt-60 sources was constructed and installed in Stockholm in 1968. That unit was primarily intended for use in functional brain surgery for the section of deep fiber tracts, as in the treatment of intractable pain and movement disorders.

As sophisticated neuro-imaging (computerized tomography, magnetic resonance imaging and positron emission tomography) evolved, Leksell realized the potential of Gamma Knife® surgery in the treatment of neoplastic and vascular disorders.

Since 1968, Gamma Knife® has established its efficacy and safety and offers an operative system that makes the depths of the brain more accessible. More than 600,000 patients have been treated using Gamma Knife® surgery.

The Leksell Stereotactic Frame – Why it Matters

Patients looking for choices in radiosurgery usually want to know more about the head frame used in the Gamma Knife treatment.

First, about the frame – It is a lightweight (one and a half pounds) titanium frame which can be safely worn during an MRI scan. It is attached to the head using four fine-point titanium or aluminum pins. The frame is attached under local anesthetic and mild sedation after the patient is admitted to the Gamma Knife Treatment Preparation room. It is necessary for the frame to be attached before the patient gets a CT or MRI scan and it must be worn during the treatment. When the treatment procedure is completed (typically within three to four hours after frame placement) the staff immediately removes the frame and a light dressing is applied to the pin sites. Tiny puncture wounds in the scalp usually heal completely over in less than a week, and are virtually unnoticeable a few hours after the procedure. Post-procedure pain at the pin sites is rarely encountered, and will resolve in a few days if present at all. The surgeons usually prescribe mild pain killers in case minor pain is encountered.

Why use a frame at all? This may be the most important question a patient can ask when choosing the treatment modality. The stereotactic frame has been used for this procedure for over 40 years. It is the only system that absolutely GUARANTEES that there is no movement of the target during the Gamma Knife treatment. When properly attached, the stereotactic frame will not move even a fraction of a millimeter during the scan and treatment, insuring that the treatment plan is accurately and precisely delivered every time.

Frameless Systems – There are various systems that do not use a frame. While the patient is secured to some degree against movement, this security is not guaranteed. As a result, these systems require that frequent imaging must be done during the treatment – and this imaging must be instantly analyzed by complex software in real time to correct for motion. Modern frameless systems are sophisticated and generally reliable, but can never match the frame in terms of consistent accuracy and reproducibility.

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