Gamma Knife Radiation Therapy for Pituitary Tumors - Introduction

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Gamma Knife radiosurgery is a method for delivering focused radiation therapy to a variety of tumors and lesions in the brain and to pituitary tumors. This discussion will address the general use of Gamma Knife in patients with a pituitary tumor. Pituitary radiation is usually administered as adjunctive (additional) therapy for patients who have a residual tumor and/or persistent excessive hormone secretion such as Cushing's Disease, acromegaly, Nelson's syndrome or prolactinoma.

Pituitary radiation is most commonly administered after surgery or if there is an inadequate response to medical therapy (prolactinoma). The Gamma Knife was developed in 1970 by a neurosurgeon, Dr. Lars Lexsell. With the development of MRI, the dose planning of the radiation field has been modified to improve the accuracy of focusing the radiation field.

The size and location of the tumor are the limiting factors in determining if Gamma Knife radiation is appropriate; the tumor cannot be too close to the optic chiasm (eye nerves) because of the risk of damage to vision. Gamma Knife radiation treatment is usually administered as a single treatment which requires most of one day. The patient has a stereotactic frame placed on the head, an MRI scan is used to plan the precise field which will be exposed to radiation and the treatment is given over 1 to 2 hours. Because most pituitary adenomas are benign (non-cancerous), it is thought that a single dose of focused radiation is adequate therapy. Administering the radiation in one session is more convenient for the patient and may be more cost effective considering time lost from work. Focused radiation should avoid damage to the hypothalamus (the portion of the brain which regulates the pituitary gland) and other parts of the brain; Gamma Knife exposes a much smaller amount of the brain to radiation, thus decreasing the risks. Because this method of delivering radiation has a very steep fall off of radiation, the optic nerves and optic chiasm are spared from receiving harmful doses of radiation. In some patients, a discrete tumor can be targeted and the normal gland can be spared from receiving significant radiation. In patients who have persistent excessive hormone secretion but no discrete tumor, the entire pituitary gland is usually targeted for radiation.