Fractionated Stereotactic Body Radiation Therapy (SBRT) Provides Excellent Local Control for Peri-adrenal and Adrenal Metastases

Abstract

The adrenal gland is a common site of metastatic disease given its rich vascular supply, most notably with non-small cell lung cancer (NSCLC) histology. Progression-free and overall survival improvements with treatment of oligometastatic sites of disease have piqued interest in aggressive local therapies for these “intermediate” disease states. Stereotactic Body Radiation Therapy (SBRT) deposits tumoricidal radiation doses within the target volume, with minimal exposure to nearby organs at risk. Therefore, SBRT is dosimetrically an ideal radiation modality to provide local control (LC) for metastases in periadrenal and adrenal sites. However, limited data exist supporting fractionated SBRT for metastases in these locations. This study investigates LC rates with fractionated SBRT targeting periadrenal and adrenal metastases. From 2010-2018, 33 patients with periadrenal or adrenal metastases and limited oligometastatic (<5 sites) disease were consecutively treated with SBRT at a single institution. 3 patients were excluded for limited imaging or follow up data after treatment. Patients’ demographic, clinical, and treatment data were abstracted from their charts. Local and distant failures on imaging studies were recorded to evaluate disease control. Toxicity was scored using CTCAE v 4.0. Overall survival (OS), progression free survival (PFS), and local failure free survival (LFFS) were estimated by Kaplan-Meier methods. Impact of clinical and treatment variables were calculated using Kaplan-Meier statistics and compared with log rank tests. Thirty patients (8 female, 22 male) with various primary histologies (12 hepatocellular carcinoma; 4 NSCLC; 3 melanoma; 9 other) received fractionated SBRT for definitive treatment of their metastases. Prescription doses were 30-54 Gy in 3-5 fractions, with mean and median BED10 of 75.8Gy and 60 Gy, respectively (range 48-151.2 Gy). Treatment related toxicities were minimal, with grade 1 or 2 nausea in 12 patients, no grade 3 GI toxicity, and no renal toxicity. Local control (LC) was achieved at the treated site in 25 patients (83.3%), with a median LFFS not reached (mean of 41 months). Median PFS was 12.3 months and median OS was 19.7 months. Histology and maximum tumor size did not significantly impact oncologic outcomes. Treatment with immunotherapy showed a non-significant trend towards improving OS (p=0.138), with no impact on LC or PFS. BED10 above 80 Gy showed a non-significant trend towards improved LC (p=0.177), without improvement in OS or PFS. Fractionated SBRT provides excellent tumor control with minimal toxicity in peri-adrenal and adrenal gland metastases. Dose schedules with BED10 above 80 Gy should be considered for definitive therapy to provide optimal local control. With modern systemic treatments improving survival outcomes in patients with oligometastatic disease, this treatment approach warrants further investigation in appropriately selected patients.