Intensity-modulated Radiotherapy for Pituitary Somatotroph Adenomas

Abstract Objective To summarize our experience in the treatment of pituitary somatotroph adenomas by fractionated intensity-modulated radiotherapy (IMRT), describe the treatment outcomes, and determine predictors. Methods and Materials Patients with pituitary somatotroph adenoma treated by IMRT in our institution from August 2009 to January 2019 were reviewed. A total of 113 patients (37 male) were included in this study. The median age was 33 years (range 12-67 years). A total of 112 patients had not achieved complete remission after surgery, and 1 patient was treated by radiotherapy (RT) alone because she refused to surgery. The median growth hormone level was 8.6 ng/mL (range 2-186 ng/mL) and the median insulin-like growth factor (IGF)-1 level was 732 ng/mL (range 314-1485 ng/mL) pre-RT. The radiation doses to clinical target volume were usually 50-56 Gy in 25 to 30 fractions and to gross tumor volume were 60.2 Gy in 28 fractions while simultaneous integrated boost-IMRT used. After RT, the patients were followed up with endocrine testing every 6 to 12 months and magnetic resonance imaging annually. Endocrine complete remission was defined as a normal sex- and age-adjusted IGF-1 level without any pituitary suppressive medications. The outcomes including endocrine remission and new hypopituitarism after RT were recorded. The median follow-up time was 36 months (range 6-105.5 months). Results The endocrine complete remission rates of IGF-1 at 1, 2, 3, and 5 years were 6%, 22.8%, 48.6%, and 74.3%, respectively. The median time to complete remission was 36.2 ± 3.8 months. The tumor control rate was 99% during the follow-up. The overall incidence of RT-induced hypopituitarism was 28.3% at the last follow-up. Univariate and multivariate analysis demonstrated that tumor sizes before RT, pre-RT IGF-1 level, and age significant predicted the endocrine remission. Conclusions IMRT is a highly effective treatment for pituitary somatotroph adenoma. Endocrine remission rate, tumor control rate, the median time to remission and hypopituitarism incidence are similar to stereotactic radiosurgery. Age and IGF-1 level before RT were significant predictive factors in endocrine remission.