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

Abstract

Toanalyze factors associated with post-stereotactic radiosurgery (SRS) hypopituitarism among radiation-naïve patients with pituitary adenomas who underwent single-fraction SRS between 2007 and2014. 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 24months of endocrine follow-up. Forty patients (41%) had hormone-secreting tumors; 57 patients had nonsecreting tumors (59%). The median prescription isodose volume was 2.8cm3 (interquartile range [IQR], 1.3-4.7); the median tumor margin dose was 20Gy (IQR, 15-25Gy). The median follow-up after SRS was 48months (IQR, 34-68months). Twenty-seven patients (28%) developed pituitary insufficiency at a median of 22months (IQR, 12-36months) after SRS. The rate of new endocrine deficits was 17% at 2years (95% confidence interval [CI] 10%-25%) and 31% at 5years (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 <11.0Gy at 2years was 2% (95% CI 0%-4%) and at 5years was 5% (95% CI 0%-11%), whereas rate of hypopituitarism for patients with a mean gland dose of ≥11.0Gy at 2years was 31% (95% CI 17%-43%) and at 5years was 51% (95% CI 34%-65%). 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 < 11.0Gy whenever feasible may lower the incidence of new hormonal deficits after pituitary adenoma SRS.