Local control following stereotactic body radiotherapy to adrenal oligometastases.

Abstract

447 Background: The role and associated risks of stereotactic body radiotherapy (SBRT) for adrenal metastases remain unclear. We report our single institution experience and report novel techniques to selectively dose-escalate treatment while concurrently minimizing dose to nearby critical structures. Methods: We retrospectively reviewed patients with evidence of metastatic adrenal disease originating from any primary histology treated with SBRT from 2013 to 2018. The primary endpoint was local control (LC). Secondary endpoints were disease-free survival (DFS), overall survival (OS), and treatment-related toxicity. LC, DFS, and OS were calculated with Kaplan-Meier analysis. Univariable and multivariable analysis were performed with long-rank and Cox proportional analysis. Results: A total of 45 adrenal metastases in 41 patients received SBRT. The median age was 67 years (range 40-80). The most common primary histologies were non-small cell lung cancer (51%), renal cell carcinoma (24%), and small cell lung cancer (10%). The median gross internal and planned target volumes were 21.23cc (range, 3.1–124.7cc) and 31.68cc (range, 5.2–175.9cc), respectively. The median dose administered was 50 Gy with 30 (67%) lesions receiving ≥50 Gy and 14 (31%) receiving 60 Gy. Twenty-six (58%) lesions were selectively dose-painted. Of the 42 simulations, 26 (62%) were treated supine, 5 (12%) prone, and 11 (26%) in the left lateral decubitus position. At a median follow-up of 10.5 months, there were 3 local recurrences (LR). 12-month LC rate was 96% with a median LC of 35 months. All three LR were in the metachronous, oligometastatic patients. One patient developed a hypertensive crisis which required intravenous antihypertensives. Conclusions: Adrenal SBRT for oligometastatic disease is a reasonable, noninvasive option with excellent LC and minimal toxicity. Lesions in close proximity to radiosensitive organs may benefit from techniques, such as dynamic patient positioning and selective dose-painting, for further dose-escalation to optimize LC rates while simultaneously limiting associated toxicity risks.