Hypopituitarism After Single-Fraction Pituitary Adenoma Radiosurgery: Dosimetric Analysis Based on Patients Treated Using Contemporary Techniques

Purpose: To analyze factors associated with post-stereotactic radiosurgery (SRS) hypopituitarism among radiation-naive patients with pituitary adenomas who underwent single-fraction SRS between 2007 and 2014. Methods and Materials: This was a retrospective review of 97 patients having single-fraction SRS from 2007 until 2014. Eligible patients had no history of prior radiation, normal age-and sex-specific pituitary function before SRS, and at least 24 months of endocrine follow-up. Forty patients (41%) had hormone-secreting tumors; 57 patients had nonsecreting tumors (59%). The median prescription isodose volume was 2.8 cm 3 (interquartile range [IQR], 1.3-4.7); the median tumor margin dose was 20 Gy (IQR, 15-25 Gy). Results: The median follow-up after SRS was 48 months (IQR, 34-68 months). Twenty-seven patients (28%) developed pituitary insufficiency at a median of 22 months (IQR, 12-36 months) after SRS. The rate of new endocrine deficits was 17% at 2 years (95% confidence interval [CI] 10%-25%) and 31% at 5 years (95% CI 20%-42%). Male sex (hazard ratio [HR] 2.38, 95% CI 1.05-5.26, P=.04), smaller pituitary gland volume (HR 0.99, 95% CI 0.99-0.99, P=.01), and higher mean pituitary gland dose (HR 1.31, 95% CI 1.16-1.47, P<.001) were associated with post-SRS hypopituitarism in multivariable analysis. The rate of hypopituitarism for patients with a mean gland dose of <11.0 Gy at 2 years was 2% (95% CI 0%-4%) and at 5 years was 5% (95% CI 0%-11%), whereas rate of hypopituitarism for patients with a mean gland dose of >= 11.0 Gy at 2 years was 31% (95% CI 17%-43%) and at 5 years was 51% (95% CI 34%-65%). Conclusions: Hypopituitarism after pituitary adenoma SRS increases in a time- and dose-dependent manner. Reducing the radiation exposure to the identifiable gland to a mean dose <11.0 Gy whenever feasible may lower the incidence of new hormonal deficits after pituitary adenoma SRS. (C) 2018 Elsevier Inc. All rights reserved.