Marginless 5-Fraction Robotic Radiosurgery for Unfavorable Nonfunctioning Pituitary Macroadenoma: 5-year Outcomes from a Single Institution Protocol

Abstract

Nonfunctioning macroadenoma is a commonly diagnosed pituitary tumor. Resection is the favored treatment, with radiosurgery often utilized for residual or progressing disease. Long-term outcomes are established for single-session radiosurgery, but mature outcomes are lacking for multisession radiosurgery. We report our institution's 5-year efficacy and safety results for unfavorable nonfunctioning pituitary macroadenoma patients treated with marginless 5-fraction robotic radiosurgery. Between 2010-2020, patients who completed marginless 5-fraction radiosurgery for the treatment of unfavorable nonfunctioning pituitary macroadenomas were included. A tumor was considered unfavorable if the gross tumor volume (GTV) was larger than 5 cc or if it closely approached a critical structure (optic apparatus, brainstem or pituitary gland). Local control was calculated using the Kaplan-Meier Method. Twenty predominately female patients (60%), age from 21-77 (median: 53 years) were included in this study. All underwent primary resection. Indications for radiosurgery included unresectable recurrence (85%) and residual disease progression (70%). Median tumor volume was 3.4 cm3 (range: 0.3-20.8 cm3) and 40% of the tumors were suprasellar. A mean dose of 28.8 Gy (range: 25 Gy-30 Gy), was delivered to a median isodose line of 80% (range: 75%-89%). The median optic chiasm maximum point dose was 21.8 Gy (range: 12.0-25.9 Gy). Toxicity was minimal with 12 patients (40%) developing acute short-lived headaches and 1 patient (5%) developing a brief ipsilateral 6th nerve palsy. There was no radiation induced optic or pituitary dysfunction identified in this cohort. At a median follow up of 5 years local control was 95%. There was 1 in-field failure pathologically confirmed following surgery for pituitary tumor hemorrhage and 2 radiographically confirmed out-of-field failures in patients with large tumors (>20 cc). The treatment of unfavorable nonfunctioning pituitary macroadenoma with marginless 5-fraction robotic radiosurgery provides excellent local control to date, with minimal toxicity. However, tumors with GTV's greater than 20 cc may require conventionally fractionated treatment with a margin to optimize local control.