Endocrine Abstracts

Background: Proton beam therapy (PBT) provides high doses of radiation to the targeted tissues while minimizing exposure to surrounding structures. Although rarely used in patients with functional pituitary adenomas (FPA) it might be nessesary in certain clinical situations. There is paucity of data regarding short- and long-term endocrinologic outcomes.

Objectives: In patients undergoing PBT, determine rate of remission of FPA(normal hormonal values off medical suppressive therapy [MST]), control of FPA (reduction in MST and remission) and rate of hypopituitarism.

Methods: Review of prospectively set up database of adults from tertiary referral center with FPA 2015. Baseline data included demographics, tumor pathology, prior history of surgery/radiation, MST, hormonal data and incidence of pituitary insufficiencies (PI). Biochemical hormonal data, change in MST, remission of functional excess, and incidence of new PI was abstracted at 6 months, and 1, 2, 3, 4, 5 years, and up to two additional time points up to 2023. Statistical analysis includes descriptive statistics presented as number (%) and median [IQR].

Results: Twelve patients with FPA of total 40 pathologies of pituitary origin underwent PBT. Median age of patients was 43.9 years old [30.8, 56.4], median follow-up was 24 months [12, 60]. Median PBT Gy was 52.2 [50.4, 54], in median of 28 fractions. Tumors included GH-secreting in 6 (50.0%), followed by two (16.7%) ACTH-secreting, two (16.7%) PRL-secreting, one (8.3%) TSH-secreting, and one (8.3%) plurihormonal. All patients had prior surgeries (range 1-4), 3 (25%) had previous photon radiation. Eleven (91.7%) were uncontrolled despite 9 (75%) being treated with MST. The 3 (25%) patients who were not on MST had increase in size of their tumor prompting PBT. At least one PI was observed at baseline in 9 patients (75%), secondary hypogonadism most common (7, 58.3%). At 6 months remission occured in 2 (16.7%). At the end of follow-up, 3 (25%; 2 GH-secreting and 1 ACTH-secreting) had achieved remission, 2 (16.7%, 1 GH-secreting and the TSH-secreting) were controlled, with MST reduced, 4 (33.3%) were controlled but MST not reduced, and persistent hyperfunction was observed in 3 (25.0%). Only one patient (16.7%) without PI at baseline developed adrenal insufficiency at 3-years post-treatment.

Conclusion: PBT is a reasonable consideration for treatment of selected FPA for control or reduction of MST need with little newly developed PI, recognizing the already high initial prevalence of PI in this cohort a still limited follow-up.