Introduction

Radiation therapy for a secretory pituitary adenoma is most commonly used as adjunctive treatment for residual disease after pituitary surgery or unrespon-siveness to medical therapy as may occur with a prolactin (PRL) secreting adenoma. Advances in the techniques of transsphenoidal removal of a pituitary adenoma have resulted in improved surgical results and safety for the patient. Despite these advances, in patients with a large invasive lesion, particularly with invasion of the cavernous sinus, it must be anticipated that additional treatment(s) will be necessary to control the disease. Thus, patients with an adenoma that is large or unresponsive to medical therapy should be informed of the need for multimodal therapy.

From: Management of Pituitary Tumors: The Clinician's Practical Guide, Second Edition Edited by: M. P. Powell, S. L. Lightman, and E. R. Laws, Jr. © Humana Press Inc., Totowa, NJ

Conventional fractionated radiation to a pituitary tumor has been used for more than 90 yr. The initial approaches used horizontally opposed temporal ports that resulted in effective control of some tumors but also caused radiation-induced damage to the carotid arteries and temporal lobes in some patients. The technique was modified by the introduction of multiport methodology followed by rotational and conformal techniques that are currently employed. Today, conventional radiotherapy is administered using a linear accelerator. Conventional radiotherapy to pituitary adenomas was usually beneficial in reducing the risk of continued growth and, in some cases, control of hormone hypersecretion. However, immediate or prompt control of hormone hypersecretion does not usually occur, and for several years, the patient experiences persistent active disease with its resultant complications.

In the 1960s, Dr. Lars Leksell developed the Gamma Knife as a method of delivering focused radiotherapy (radiosurgery), which consists of a large number of cobalt sources collimated to focus on a target area small enough to include a lesion in the sella turcica. Gamma Knife radiosurgery has achieved widespread use throughout the world and is theoretically ideal to treat a small pituitary lesion and reduce radiation exposure to the temporal and frontal lobes of the brain (1-4). See Figs 1 and 2.

This discussion includes indications for Gamma Knife treatment of patients with a secretory pituitary adenoma, the need for adjunctive medical therapy to control hormone hypersecretion, the need for regular monitoring for development of new pituitary hormone deficiency, and the outcomes of Gamma Knife therapy.

I Radioactive cobalt

Fig. 2. The principals of focused targeting of gamma rays using Gamma Knife.

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