Gamma Knife - Definition and Applications

Definition and Applications

Radiation oncologists make use of highly sophisticated, highly precise and complex instruments, such as stereotactic devices, linear accelerators, the gamma knife, computers and laser beams. The highly precise irradiation of targets within the brain is planned by the radiation oncologist based on images, such as computed tomography (CT), magnetic resonance imaging (MRI), and angiography of the brain and body. The radiation is applied from an external source, under precise mechanical orientation by a specialized apparatus. Multiple beams are directed (collimated) and centered at the intracranial or extracranial lesion to be treated. In this way, healthy tissues around the target are relatively spared.

Stereotactic radiosurgery generally utilizes gamma rays or x-rays. There is also increasing interest in using particle therapy such as protons and carbon ions for radiosurgery, though this is not widely available.

Patients can be treated within one to five days and as an outpatient. By comparison, the average hospital stay for a craniotomy (conventional neurosurgery, requiring the opening of the skull) is about 15 days. Radiosurgery costs less than conventional surgery, and with much less morbidity, e.g. mortality, pain and post-surgical complications, such as hemorrhage and infection. The period of recovery is minimal, and in the day following the treatment the patient may return to his or her normal life style, without any discomfort. However, radiosurgery is not without limitations and disadvantges. It is difficult and dangerous to treat masses larger than 3 cm because it will require very high doses of radiation. Fractionated radiotherapy may be a better option ideally combined with surgical debulking. The duration of time required to achieve the desired effects is much longer than surgery; it can take up to two years for arteriovenous malformations. During that time, the patient remains at risk for a rebleed. For treatment of tumors, it is important to remember that radiosurgery does not physically remove the tumor, rather stops it from growing larger. Therefore, it is not a good option when the tumor presents with significant mass effect on vital structures of the brain or spinal cord and when it causes increased intracranial pressure. Open surgery is needed to relieve pressure, remove the tumor totally or debulk (reduce it in size) it to make it a better target for radiotherapy or radiosurgery. Open surgery and radiosurgery are often used in conjunction for many types of brain tumors. Radiosurgery is a particularly good option for patients who are poor surgical risks due to their medical co-morbidities.

Stereotactic radiosurgery can successfully treat many different types of tumors, both benign and malignant. The malignant brain tumors treated most often are the "brain metastases" or tumors that have spread to the brain. A study in 2008 by the University of Texas M. D. Anderson Cancer Center indicated that stereotactic radiosurgery (SRS) and whole brain radiation therapy (WBRT) for the treatment of metastatic brain tumours have more than twice the risk of developing learning and memory problems than those treated with SRS alone. “While both approaches are in practice and both are equally acceptable, data from this study suggest that oncologists should offer SRS alone as the upfront, initial therapy for patients with up to three brain metastases,”