Gamma knife and linear accelerator stereotactic radiosurgery

Ano de publicação: 2002

INTRODUCTION:

Thanks to the technological evolution of the different imaging techniques, which are now increasingly precise, the surgical or, more specifically, neurosurgical treatment of certain brain lesions has made tremendous strides. The main challenge in stereotactic radiosurgery (SRS) was to offer greater efficacy while at the same time minimizing the risk. The emergence of approaches using various types of rays (electron, gamma, etc.) and the constant evolution of nuclear physics fostered the development of a new approach in neurosurgery stereotactic radioneurosurgery. This type of treatment consists in exposing a lesion of small volume, determined by three -dimensional imaging, to a single high dose of ionizing rays while at the same time minimizing the dose absorbed by the surrounding structures. What is unique about SRS is that it allows one to treat lesions (e.g., the destruction of tumors) without making a surgical incision. With SRS, very delicate and hard -to-reach areas can be treated (e.g., near the optic chiasma) where surgery is not possible because of the risks inherent in the surgical procedures (e.g., hemorrhage, irreversible lesions). The fact that the procedure involves less traumatic intervention conditions (local anesthesia) is the other attractive feature of this technique. The cyclotron, linear accelerator and gamma knife are the three main types of instruments used in SRS. They differ from each other by their radiation source and their mobility in relation to the patient.

METHODOLOGY:

A literature search was performed in the Medline, Cochrane Library, Embase and HealthStar databases, and was supplemented with reports from a number of health technology assessment agencies that had looked at SRS. Upon examining the relevant scientific data, it was observed that: -There has been a very large number of study reports on the efficacy of SRS, especially in the past ten years; -Almost all of the studies have been of the retrospective type, with no randomization or comparison; -Very few or even no comparative studies have examined the use of the gamma knife and linear accelerator (adapted or dedicated) for specific indications. Very few economic studies comparing the various instruments have been carried out, and for the most part, they are considered in the reports published by national assessment agencies.

CONCLUSIONS:

The efficacy of SRS has been established for a certain number of indications, including brain metastases, arteriovenous malformations, as an alternative to conventional surgery in cases of interventional difficulties, and in the prevention of the complications of the standard treatments in cases of meningioma and vestibular schwannoma. SRS is a promising approach in the treatment of pituitary adenomas, certain skull base tumors, and specific functional disorders. Given the evolution of the technologies and the costs associated with SRS, the instruments that might best meet the efficacy and safety criteria are the dedicated linear accelerator and the gamma knife. The use of an adapted linear accelerator is possible but limited in cases of lesions in very close proximity to sensitive structures, since the manipulations required to adapt the equipment in order to perform SRS can be a source of imprecision when focussing the beams. Furthermore, the need to perform quality control before each treatment lengthens the treatment time. Presently, SRS facilities are clearly needed in Québec. If we consider all the lesions eligible for SRS on the basis of the existing data and evaluations, more than 300 patients could benefit from SRS. Even if, in theory, the gamma knife and dedicated linear accelerator are both more suitable for the various indications for SRS, technological developments in the specific area of SRS (especially in the case of the dedicated linear accelerator) and the lack of randomized, controlled trials concerning a given indication do not permit us to conclude that either of these instruments is superior to the other from the standpoint of efficacy. However, the degree of precision offered by the gamma knife permits the treatment of lesions that are no more than 2 mm in size and which touch vital structures, such as the cranial nerves, optic chiasma and brainstem, without (theoretically) causing any injury to healthy tissues. Given the current knowledge about the clinical, economic, technical and epidemiological aspects and given the need to adequately fulfill the offer of SRS services and to adequately meet research needs, the Agency recommends that a specialized radiosurgery centre with a gamma knife be created at a university hospital. Where this specialized centre will be set up will depend on geographical and/or functional accessibility and well-established service pathways. The institution chosen must have the necessary logistical wherewithal (structural and professional) needed to perform this type of treatment. The mandatory presence of a multidisciplinary team (neurosurgeon, neuroradiologist, radiation therapist, radiophysicist, paramedical personnel), the need to provide continuous patient management quality and the need to promote the acquisition of new professional skills clearly warrant creating the centre at a university hospital.

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