Adrenal SBRT: a multi-institutional review of treatment outcomes and toxicity.

The adrenal glands are a common site of metastatic disease. Definitive treatment for oligometastatic disease using ablative radiotherapy is becoming common in modern radiation oncology practice. However, most data on the treatment of adrenal metastases are limited to single institution reports. Furthermore, delivering ablative radiotherapy doses to intra-abdominal lesions can be challenging due to the proximity of the gastrointestinal tract. We report the outcomes of a multi-institutional cohort of patients treated with definitive radiotherapy for adrenal metastases, primarily using 10 fraction regimens. Retrospective review of institutional databases revealed 29 lesions in 27 patients were treated from 2005 to 2018 at two institutions. Outcome data, including local control, disease-free, and overall survival were abstracted from the medical record system. Toxicity was graded using CTCAE v5.0. Detailed radiotherapy data was abstracted from the treatment planning systems. The median dose was 50 Gy in 10 fractions. Actuarial 1 and 2 year local control was 86% and 76% respectively. The median overall and disease-free survival were 22.8 and 5.6 months respectively. There were no associations identified between local failure and GTV and PTV physical or biologic effective dose. Two patients developed late Grade 3 gastrointestinal toxicity. High dose radiotherapy to adrenal metastases is a feasible treatment with excellent local control and a reasonable safety profile. For lesions in close proximity to gastrointestinal structures, moderately hypofractionated 10 fraction regimens may be a reasonable compromise between local control and toxicity.