Intensity-Modulated Radiotherapy (IMRT) for the Treatment of Cushing's Disease

Abstract

Aim to investigate the efficacy and toxicity of IMRT in treating Cushing's Disease (CD). A total of 78 of 115 patients with CD treated with IMRT at our institute from April 2012 to August 2021 were included in the study. The radiation doses were usually 45-50 Gy in 25 fractions. After IMRT, endocrine evaluations were performed every 6 months and magnetic resonance imaging (MRI) annually. Endocrine remission was defined as suppression of 1 mg dexamethasone test (DST) or normal 24-hour urinary free cortisol level (24hUFC). Endocrine recurrence was considered when patients who have reached hormonal remission showed no suppression of 1 mg DST and relapse of clinical features. The outcome of endocrine remission, tumor control and complications were retrieved from medical record. At a median follow-up time of 36.8 months, the endocrine remission rate at 1, 2, 3 and 5 years were 28.5%, 50.2%, 62.5% and 74.0%, respectively. The median time to remission was 24 months (95% CI: 14.0-34.0). Endocrine recurrence was found in 5 patients (13.5%) till the last follow-up. The recurrence-free rate at 1, 2, 3 and 5 years after endocrine remission was 98.2%, 93.9%, 88.7% and 88.7%, respectively. The tumor control rate was 98%. The overall incidence of new onset hypopituitarism was 23.1%, with hypothyroidism serving as the most common individual axis deficiency. Univariate analysis indicated that only higher Ki-67 index (P = 0.044) was significant favorable factors for endocrine remission. But no prognostic factors for endocrine remission were found in the multivariate analysis. IMRT was a highly effective second-line therapy with low side effect profile for CD patients. Endocrine remission, tumor control and recurrence rates were comparable to previous reports on FRT and SRS.