7910 Hypopituitarism Incidence Following Proton Beam Radiotherapy for Treatment of Chordomas and Parasellar Meningiomas

Abstract Disclosure: J. Herndon: None. W.G. Breen: None. N. Laack: None. W.S. Harmsen: None. D.Z. Erickson: None. Background: Treatment of chordomas and parasellar meningiomas includes surgical resection and/or various forms of radiotherapy. Proton beam therapy (PBT) is able to provide higher doses of radiation to the targeted tissues while better sparing surrounding structures, potentially facilitating decreased toxicity. While proton utilization has increased, there is a paucity of data regarding short- and long-term endocrinologic outcomes in these patients. Objective: Determine rate of hypopituitarism in patients with chordomas and parasellar meningiomas undergoing PBT. Methods: A prospectively maintained radiation database including adult patients treated with PBT since 2015 at a tertiary referral center for chordomas and parasellar meningiomas was reviewed. Data collected at baseline included demographic data, tumor diagnosis and pathology, prior history of surgery/radiation, radiation treatment, biochemical hormonal data, and incidence of pituitary insufficiencies (PI). Biochemical pituitary hormonal data and incidence of new PI was recorded at 6 months, 1 year, 2 years, 3 years, 4 years, 5 years, and up to two additional time points up to 10 years post-PBT. Statistical analysis includes descriptive statistics presented as number (%) and median [IQR]. Results: Of 177 patients with sellar/parasellar masses with sufficient endocrine data who underwent PBT, a total of 64 patients (36.2%) were included; 40 (62.5%) with parasellar meningioma and 24 (37.5%) with chordoma. Median age of patients was 49.5 years old [37.7, 63.2], and 44 (68.8%) were female. Median follow-up was 24 months [12, 36]. Prior to PBT, 52 patients (81.3%) were treated surgically, 5 (7.8%) had prior fractionated photon or gamma-knife radiation therapy. At baseline 10 patients (15.6%) exhibited PI in at least one pituitary axis, most commonly secondary hypogonadism (7, 70%). Median PBT total prescribed dose was 54 Gy [50.4, 70.0] in a median of 30 [28, 35] fractions. Cumulative incidence of newly diagnosed PI at follow-up was 4.7% at 6 months, 9.4% at 1 year, 14.1% at 2 years, and 17.2% at 3+ years. No patients with PI at baseline developed new deficiencies. Among the 11 patients (17.2%) who developed new PI, 17 various deficiencies were recorded (range 1-3 per patient), including hypogonadism (8, 47.1%), hypothyroidism (6, 35.3%), and adrenal insufficiency (4, 23.5%). No growth hormone deficiency was clinically diagnosed, however IGF-1 levels decreased from baseline at the follow-up (when available) by a median of -11.8 ng/mL at 6 months (n = 12), -3.0 at 1 year (n = 12), -17.0 at 2 years (n = 7), -30.5 at 3 years (n = 4), -55.0 at 4 years (n = 3), and -37.5 at 5 years (n = 2). Conclusion: Incidence of newly developed PI in chordomas and parasellar meningiomas following PBT for adult patients after median initial follow up of 2 years was low, however extended follow up data are necessary. Presentation: 6/1/2024