Modern Radiation Therapy for Pituitary Adenoma: Review of Techniques and Outcomes

Pituitary adenomas are benign tumors arising in the adenohypophysis and comprise 8%-20% of all reported primary brain tumors in the west. Transsphenoidal surgery with an aim to achieve complete tumor resection is the recommended first-line treatment for nonfunctioning as well as secretory pituitary adenoma. External beam radiation therapy (RT) has been demonstrated to be an effective treatment modality for pituitary adenoma, uncured by surgery and/or medical therapy, providing excellent long-term local control (>90%), but lower and variable rates (50%-80%) of biochemical remission in secretory tumors. The adoption of pituitary RT in the community has been limited due to concerns regarding potential late toxicity and long latency in normalization of hormonal hypersecretion. Over the years, technological advances in RT planning and delivery have resulted in progressive conformation of high doses to the target tissues while sparing adjacent neurovascular structures providing a favorable therapeutic index. The choice of RT technique should be based on size, site, and availability of infrastructure and expertise, with no significant differences between fractionated approaches and stereotactic radiosurgery (SRS). In contemporary clinical practice, the recommended dose of fractionated RT for pituitary adenoma is 45-50.4Gy in 25-28 fractions delivered over 5-6 weeks using modern high-precision techniques. The recommended dose of SRS given in a single fraction is 12-14Gy for nonfunctioning adenomas and 16-20Gy for secretory tumors. Late toxicity of pituitary RT includes hypopituitarism, neurocognitive impairment, neuropsychological dysfunction, optic neuropathy, cerebrovascular accidents, and second malignant neoplasms. Hence, RT in pituitary adenoma should be offered only to patients with residual, recurrent, progressive, or high-risk tumors with careful assessment of the benefit-risk ratio by an experienced multidisciplinary neurooncology team.