Stereotactic surgery Radiosurgery Gamma Knife Eugen Kvasnak, PhD. Department of Medical Biophysics and Informatics 3rd Medical Faculty of Charles University

Stereotactic surgery means operations in three dimensional planar system (axis x,y,z). Any structure or organ, for example brain is placed into a three dimensional frame. A very fine needle is attached to this frame. If we know coordinates of any structure in the brain, we can hit it with a tip of the needle only by setting coordinates of the structure.

Organs suitable for this surgery For stereotactic surgery is suitable brain, because it is placed in the scull. The frame for stereotactic surgery can be firmly attached to the scull, so there is no movement between the scull and the frame. The brain does not move inside the scull too. So the result is that the brain and the frame for stereotactic surgery don’t move each other.

Finding the coordinates CT scan and NMRI is used. If the organ move out of the frame, coordinates can not be set and the stereotactic surgery is not possible. Radiosurgery is carried out through the cooperative efforts of a neurosurgeon, radiation oncologist and physicist. Initial consultation will help you determine if GK radiosurgery is appropriate, effective and safe Every patient should have information about all applicable treatments, the expected outcomes, risks, costs and the natural history of the untreated disease process. The decision of treatment is up to the patient.

Radiosurgery The computer software reduces the treatment plan to a list of simple instructions to guide the gamma rays to the target. The patient’s stereotactic head frame is fixed within the collimator according to these instructions. Usually several shots are used to cover the entire target volume. Total treatment time varies from 45 minutes to hours. Following treatment, the frame is removed and patients are observed overnight or are discharged home.

Gamma Knife The Gamma Knife contains 201 small Cobalt sources of gamma rays arrayed in a hemisphere within a thickly shielded structure. Collimator aims the radiation emitted by these sources to a common focal point. This is analogous to focusing the radiant energy of the sun with a magnifying glass to a hot focus. Near the glass there is not much heat, but the energy is intense at the focal point. Optical lenses can not focus gamma rays, rather individual beams are allowed to summate by overlapping at the focal point of the collimator, achieving the same effect. Collimator allows the beam focus size to be adjusted from 4 to 18 mm in size.

Gamma Knife Cure The cure of a brain tumor by radiosurgery means that the tumor loses its ability to grow and remains the same size, never growing again. The intensely focused gamma rays destroy the ability of the cells to divide. Sometimes benign tumors actually shrink over time and malignant tumors may completely disappear. Arteriovenous malformations usually occlude after focused radiosurgery. This curative process occurs over months to years.

Radiosurgery is a surgical procedure where narrow beams of radiation are targeted to a precisely defined volume of tissue within the brain. This highly focused and destructive dose of radiation is given in a single session and avoids potentially harmful radiation to surrounding brain structures.  

Radiosurgery history Professor Lars Leksell, a Swedish neurosurgeon, first developed stereotactic devices (used to guide the gamma rays) as well as the very concept of radiosurgery in the early 1950’s. Together with Borje Larsson, a physicist, Leksell built the first Gamma Knife unit in Sweden in 1968. Since that time, this non-invasive technique for the treatment of brain tumors and vascular malformations has enjoyed incredible success. More than 60,000 patients have been safely treated with focused gamma rays world-wide.

Comparison to radiation therapy Radiosurgery differs from conventional radiation therapy in several respects. With standard external beam radiation therapy techniques, tumors and much or all of the surrounding brain are treated to the same dose of radiation. The radiation dose is given in small increments over several weeks to allow normal brain tissue to recover from its effect, while tumor tissue is less likely to recover. Ultimately, the brain can absorb a maximal dose of radiation, beyond which no further treatment is advisable. There is increasing evidence that over long periods of time, high doses of radiation are harmful to normally functioning brain. The technique of Gamma Knife radiosurgery treats only the abnormal tissue, in a single session, without significant radiation to adjacent brain.

Comparison to radiation therapy Professor Leksell’s concept has proved to be a true advance in the treatment of intracranial disease. Stereotactic techniques can also be used to accurately aim fractionated doses of gamma rays or x-rays to a target; administering the treatment in small doses over days to weeks. This technique is a compromise between radiosurgery and conventional radiotherapy and is termed stereotactic radiotherapy.

Abnormalities to treat by Gamma Knife Brain tumors: Glioblastoma Anaplastic astrocytoma Gliomas / Astrocytoma Oligodendroglioma Ependymoma Pilocytic astrocytoma Meningioma Pituitary tumors Pineal region tumors Acoustic Neuroma Neuromas of the cranial nerves Glomus jugulare tumor Metastatic brain tumors Vascular abnormalities: Arteriovenous malformations Cavermous malformations Skull base tumors Invasive squamous and basal cell carcinoma Chordoma Chondrosarcoma Esthesioneuroblastoma Functional problems: Trigeminal neuralgia Parkinson's disease Essential tremor Obsessive Compulsive Disorder  Ocular tumors Uveal melanoma Orbital metastases Optic nerve sheath meningioma

How it looks…

Example of treatment Metastatic Brain Tumors: Experience has shown that surgical removal of single brain metastases followed by radiation therapy to the brain benefits patient’s quality of life and survival when compared to treatment by brain radiotherapy alone. To achieve this benefit, usually there must be control of the patient’s primary tumor. Experience has also shown that Gamma Knife radiosurgery is as effective as open surgery in the control of metastatic brain tumors when combined with radiotherapy of the brain. This is being extended to the control of multiple brain metastases. In selected individuals we do not carry out whole brain radiotherapy following Gamma Knife radiosurgery. Usually we request close follow-up by means of frequent MR images of the brain to ensure control. Recurrent or new tumor deposits can be retreated by radiosurgery.

Example of treatment frontal lobe metastasis several months after GK radiosurgery

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