2559 - Assessing Patient Outcomes of Stereotactic Radiosurgery for Pituitary Adenomas and Dosimetric Factors Associated with Post-Radiosurgery Pituitary Function - A Single Institutional Report

Purpose/Objective(s): A non-invasive stereotactic radiosurgery instrument for pituitary adenomas is an adjuvant treatment option to surgical resection. We present our long-term clinical follow up outcomes in patients with pituitary adenomas and post radiosurgery incidence of new onset associated with dosimetric variables treated via the SRS instrument.

Materials/Methods: In this IRB approved retrospective study, a total of 90 patients who underwent GK SRS treatment to pituitary adenomas: functioning/non-functioning pituitary adenoma (FPA/n-FPA) between 2010 and 2024 were included. Utilizing high resolution contrast enhanced MRI scan, highly conformal GK SRS plans were generated manually or via lightening dose optimizer. Average tumor size was 0.99±1.46 (0.06–10.29) cc. Mean marginal prescription dose to FPA & n-FPA was 24±3 (14–30) Gy and 19±3 (12–25) Gy; prescribed to 50% isodose line. GK SRS plans were evaluated for Paddick’s conformity, gradient indices (PCI, GI), maximum dose to optic apparatus and brainstem and normal tissue volume (NTV) around pituitary sella receiving V_8Gy, V_10Gy, V_12Gy, and V_14Gy. Patients were followed up for treatment response and hypopituitarism post GK in 3-month intervals.

Results: For highly conformal GK SRS plans, PCI and GI were 0.58±0.08 (0.45–0.77) and 3.02±0.41 (2.11–4.18). Average maximum dose to optic apparatus and brainstem were 6.5 Gy (maximum up to 9.1 Gy) and 5.9 Gy (18.0 Gy). Mean NTV around pituitary sella receiving V_8Gy, V_10Gy, V_12Gy, and V_14Gy were 5.29, 3.60, 2.57, and 1.85 cc. 74/90 patients had clinical outcome with mean follow up intervals of 48±41 (4–162) months. A total of 77 treatments with a 25:51 male to female ratio were evaluated; 3 repeat GK SRS. Median age was 47±14 (18–77) years. Of these, 34 (43.4%) were treated for FPA and 37 (48.7%) treated for n-FPA. Tumor local control was achieved for a total of 64 (83.1%) patients with GK, while 13 (16.9%) did not respond. 10 of 13 were FPA patients and all females. 3 of 13 underwent a second course of GK (in 6-24 months) were all female with FPA and gained local tumor control. One patient had blurred vision post GK; no patients presented with brainstem toxicity. Follow up reports showed onset of all 3 axes of hypopituitarism in 18 (24.3%) FPA patients at on average 48 months post GK; they were managed with hormone replacement. 7 of 18 FPA patients reporting hypothyroidism were female. Linear correlation between hypothyroidism and maximum dose to pituitary tumor (p=0.03) but no correlation with NTV was seen.

Conclusion: Our long-term clinical follow up results of GK SRS to pituitary adenomas is a highly effective treatment with less radiation induced hypopituitarism including reirradiation. Majority of FPA were female patients who also developed hypopituitarism after GK and related to maximum tumor dose. These clinical findings will be useful to future pituitary GK plan optimization. Detail data analysis of pituitary deficit post GK SRS in all 3 hormonal axes plus Kaplan-Meier prediction is warranted.