Radiation of bilateral adrenal metastases is associated with a high risk of primary adrenal insufficiency

Background: Adrenal metastasis is the most common adrenal malignancy and can be bilateral in up to 43% of patients. Radiotherapy (RT) is one option available to treat adrenal metastases. The risk of primary adrenal insufficiency (PAI) after adrenal RT is unclear. Objective: Determine the incidence and the timeline of PAI in patients undergoing adrenal RT. Design, Setting and Participants: Single-centre longitudinal retrospective cohort study of adult patients with adrenal metastases treated with RT between 2010 and 2021. Results: Of 56 patients with adrenal metastases treated with adrenal RT, eight (14.3%) patients developed PAI at a median of 6.1 months (interquartile range [IQR]: 3.9–13.8) after RT All patients developing PAI had either unilateral RT in the setting of contralateral adrenalectomy or bilateral adrenal RT. Patients who developed PAI received a median RT dose of 50 Gy (IQR: 44–50 Gy), administered in a median of five fractions (IQR: 5–6). Treated metastases decreased in size and/or metabolic activity on positron emission tomography in seven patients (87.5%). Patients were initiated on hydrocortisone (median daily dose of 20 mg, IQR: 18–40) and fludrocortisone (median daily dose of 0.05 mg, IQR: 0.05–0.05 mg). At the end of the study period, five patients died, all due to extra-adrenal malignancy, at a median time of 19.7 months (IQR: 16–21.1 months) since RT and median time of 7.7 months (IQR: 2.9–12.5 months) since the diagnosis of PAI. Conclusion: Patients receiving unilateral adrenal RT with two intact adrenal glands have a low risk of PAI. Patients receiving bilateral adrenal RT have a high risk of PAI and require close monitoring.