Risk-adapted single or fractionated stereotactic high-precision radiotherapy in a pooled series of nonfunctioning pituitary adenomas. High local control and low toxicity

The purpose of this work was to evaluate a prospectively initiated two-center protocol of risk-adapted single-fraction (SRS) or fractionated radiotherapy (SRT) in patients with nonsecretory pituitary adenomas (NSA). A total of 73 NSA patients (39 men/34 women) with a median age of 62 years were prospectively included in a treatment protocol of SRS [planning target volume (PTV) < 4 ccm, > 2 mm to optic pathways = low risk] or SRT (PTV ≥ 4 ccm, ≤ 2 mm to optic pathways = high risk) in two Novalis registered centers. Mean tumor volume was 7.02 ccm (range 0.58-57.29 ccm). Based on the protocol guidelines, 5 patients were treated with SRS and 68 patients with SRT. Median follow-up (FU) reached 5 years with 5-year overall survival (OS) of 90.4 % (CI 80.2-95 %) and 5-year local control and progression-free survival rates of 100 % (CI 93.3-100 %) and 90.4 % (CI 80.2-95 %), respectively. A post-SRS/SRT new visual disorder occurred in 2 patients (2.7 %), a new oculomotor nerve palsy in one pre-irradiated patient, in 3 patients (4.1 %) a pre-existing visual disorder improved. New complete hypopituitarism occurred in 4 patients (13.8 %) and in 3 patients (25 %) with pre-existing partial hypopituitarism. Pituitary function in 26 % of patients retained normal. Patients with tumor shrinkage (65.75 %) had a significantly longer FU (p = 0.0093). Multivariate analysis confirmed correlation of new hypopituitarism with duration of FU (p = 0.008) and correlation of new hypopituitarism and tumor volume (p = 0.023). No significant influence factors for occurrence of visual disorders were found. Our SRS/SRT protocol proved to be safe and successful in terms of tumor control and protection of the visual system, especially for large tumors located close to optic pathways. (orig.)