Long-Term Efficacy and Tolerability of Gamma Knife Radiosurgery for Growth Hormone-Secreting Adenoma: A Retrospective Multicenter Study (MERGE-001)

OBJECTIVE: Little is known about the long-term efficacy, prognostic factors, and tolerability of gamma knife radiosurgery (GKS) for acromegaly. The aim of this study was to investigate long-term hormonal effects, prognostic factors, and tolerability of GKS in patients with growth hormone-secreting adenoma. METHODS: A retrospective multicenter study over 25 years with a median follow-up of 85.2 months was performed. A total of 138 patients from 3 tertiary referral centers in South Korea were included in this study between 1991 and 2017. Main outcome measures were endocrine remission, endocrine control under somatostatin analogues, and hypopituitarism. RESULTS: With a mean follow-up period of 85.2 months (range, 12-304 months), overall median time to the endocrine remission and control under long-acting somatostatin analogues was 138 months and 96 months, respectively. Female sex, normal age-adjusted insulin growth factor-1 (IGF-1) <= 2, and GKS as an adjuvant treatment were significantly favorable factors for remission (P = 0.004, P = 0.001, P = 0.010, respectively). The early response group had a significantly lower proportion of normal age-adjusted IGF-1 levels >2 than did the late response group (22.2% vs. 51.7%, P = 0.035); also, the early response group had lower radiation dose than the late response group (24.3 Gy vs. 27.0 Gy, P = 0.003). The incidence of GKS-induced hypopituitarism (1 or more) was 12 of 138 patients (8.6%) at the last follow-up. CONCLUSIONS: In acromegalic patients, women with normal age-adjusted IGF-1 <= 2 and GKS as an adjuvant treatment have a better response to GKS. We should take into account the variability of radiosensitivity of the tumor according to the gender and IGF-1 level.