Single-institutional outcome-analysis of low-dose stereotactic body radiation therapy (SBRT) of adrenal gland metastases

BACKGROUND: Adrenal gland metastases are a common diagnostic finding in various tumor diseases. Due to the increased use of imaging methods, they are diagnosed more frequently, especially in asymptomatic patients. SBRT has emerged as a new, alternative treatment option in the field of radiation oncology. In the past, it was often used for treating inoperable lung, liver, prostate, and brain tumors. Meanwhile, it is also an established keystone in the treatment of oligometastatic diseases. This retrospective study aims to evaluate the effect of low-dose SBRT in patients with adrenal metastases. METHODS: We analyzed a group of 31 patients with 34 adrenal gland lesions treated with low-dose SBRT between July 2006 and July 2019. Treatment-planning was performed through contrast-enhanced CT, followed by image-guided stereotactic radiotherapy using cone-beam CT. The applied cumulative median dose was 35 Gy; the median single dose was 7 Gy. We focused on local control (LC), progression-free survival (PFS), overall survival (OS), as well as acute and late toxicity. RESULTS: Seven adrenal gland metastases (20.6%) experienced local failure, 80.6% of the patients faced a distant progression. Fourteen patients were still alive. Median follow-up for all patients was 9.8 months and for patients alive 14.4 months. No treatment-related side-effects >grade 2 occurred. Of all, 48.4% suffered from acute gastrointestinal disorders; 32.3% reported acute fatigue, throbbing pain in the renal area, and mild adrenal insufficiency. Altogether, 19.4% of the patients faced late-toxicities, which were as follows: Grade 1: 12.9% gastrointestinal disorders, 3.2% fatigue, Grade 2: 9.7% fatigue, 6.5% headache, 3.2% loss of weight. The 1-year OS and probability of LF were 64 and 25.9%, respectively. CONCLUSION: Low-dose SBRT has proven as an effective and safe method with promising outcomes for treating adrenal metastases. There appeared no high-grade toxicities >grade 2, and 79.4% of treated metastases were progression-free. Thus, SBRT should be considered as a therapy option for adrenal metastases as an individual therapeutic concept in the interdisciplinary discussion as an alternative to surgical or systemic treatment.