External Beam Radiation Therapy and Stereotactic Radiosurgery for Pituitary Adenomas

This article discusses contemporary use of external beam radiotherapy and stereotactic radiosurgery for pituitary adenoma patients. Specific techniques are discussed. In addition, indications and outcomes, including complications, are detailed.

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Recurrence of pituitary adenomas after microsurgery is reasonably common.
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Stereotactic radiosurgery (SRS) and radiation therapy provide a high rate of tumor control for recurrent or residual pituitary adenomas.
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After radiosurgery and radiation therapy for patients with functional adenomas, endocrine remission occurs in the majority of patients but the rate is not as high as that observed for tumor control.
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Delayed hypopituitarism is the most common complication after radiosurgery or radiation therapy for pituitary adenoma patients.
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Cranial neuropathies after radiosurgery or radiation therapy are fairly rare.

Key Points

Introduction

Pituitary adenomas are found in 10% to 27% of the general population. Microadenomas (less than 1 cm in maximum dimension) are usually diagnosed either after being discovered incidentally during MRI or due to hormone hypersecretion. Macroadenomas may be discovered as a result of mass effect leading to hypopituitarism, elevation in prolactin output, or a focal neurologic deficit (eg, cranial nerve dysfunction). As a distribution, microadenomas are divided equally between functioning and nonfunctioning lesions. With regard to macroadenomas, nonfunctioning lesions are more common (approximately 80%). At presentation, pituitary adenoma patients often exhibit symptoms of headache (40%–60%), visual disturbance, hypopituitarism, or rarely apoplexy.

Pituitary adenomas are some of the most challenging clinical entities that physicians have dealt with over the past century. It has been more than 100 years since Dr Harvey Cushing published his landmark book, The Pituitary Body and Its Disorders: Clinical States Produced by Disorders of the Hypophysis Cerebri . Nevertheless, pituitary adenomas remain difficult to cure with microsurgical techniques alone, and they often require multimodality treatment, which includes surgery, radiation therapy, radiosurgery, and medical management. Cushing recognized the limitations of conventional microsurgical approaches for treating intracranial tumors. Cushing and his colleagues used a device called a radium bomb to deliver a radiation therapy to intracranial tumors. Since that time, neurosurgeons and radiation oncologists, in conjunction with medical physicists, have used ionizing radiation to treat patients with recurrent or residual pituitary adenomas.

Great attention and effort in the fields of radiation therapy and SRS have been placed on the preservation of surrounding neuronal, vascular, and hormonal structures in an effort to improve the therapeutic ratio. Technical refinements for treating pituitary adenoma patients have been achieved through advances in radiobiology, neuroimaging, medical physics, and biomedical engineering. This article reviews the role of radiation therapy and SRS for pituitary adenomas ( Fig. 1 ).