Outcomes and Toxicities in Oligometastatic Patients Treated With Stereotactic Body Radiotherapy for Adrenal Gland Metastases: A Multi-Institutional Study

Abstract

Stereotactic body radiation therapy (SBRT) has emerged as an effective treatment approach in oligometastatic patients with adrenal gland metastases (AGM). Nevertheless, most of the literature reporting SBRT outcomes for AGM comes from published single institutional experience, and no specific guidelines are yet established to guide patients' inclusion and dosimetric planning.The Consortium for Oligometastases Research (CORE) is currently the largest retrospective series of patients with oligometastases (OM). Among CORE patients, those treated with SBRT for AGM were included. Adrenal metastatic burden (AMB) was defined as the sum of all adrenal GTV if more than one OM is present. BED10 was calculated with tumor alpha/beta ratio of 10. Competing risk analysis was used to estimate the risk of local recurrence (LR) and widespread progression (WP) over time, using death from any cause as a competing risk factor. Kaplan-Meier method was used to estimate the overall survival (OS), local recurrence-free survival (LRFS), and progression-free survival (PFS). Univariable and multivariable regression was used to quantify the relationship between potential predictors and the main endpoints. A P-value threshold of 0.05 was used for statistical significance.46 patients with 57 adrenal lesions were included. Median follow-up was 18.2 months. The most common primary malignancy was NSCLC. The mean (standard deviation) age at diagnosis was 65.84 (10.84) years, with 25 (53.2%) male patients and 22 (46.8%) female patients. 8 out of the 46 patients had developed more than one AGM. The most used fractionation scheme was 30 - 35 Gy in 3 - 5 fractions, and the mean prescribed BED10 was 69.37 Gy10. Median LRFS, PFS, and OS were 15.3, 5.29, and 19.1 months, respectively. The 1-year and 5-year LRFS were 65% and 25.4%, respectively. The 1-year and 5-year OS were 70% and 33%, respectively. Only 1 patient developed a Grade 3 GI toxicity. On multivariable regression, a minimum received PTV dose > 46 Gy10 was associated with an improved OS (HR 0.42, 95% CI [0.20 - 0.89], P = 0.024) and LRFS (HR 0.37, [0.18 - 0.76], P = 0.006), after adjusting for primary site. A prescribed BED10 more than 70 Gy10 was an independent prognostic factor of a lower LR rate (HR 0.31, [0.102-0.94], P = 0.039). Interestingly, AMB greater than 10 cc was an independent predictor of a lower risk WP (HR 0.29, [0.11 - 0.80], P = 0.017), after adjusting for primary histology and number of OM.SBRT to AGM is a safe procedure that achieves a satisfactory local control and survival in oligometastatic patients. The current results suggest that patients should be treated with a prescription BED10 dose of at least 70 Gy10, and a minimum PTV dose > 46 Gy10, if safely achievable. Paradoxically, AMB > 10cc was favorable, and a high AMB should not preclude the administration of a definitive course of SBRT. Prospective studies are needed to determine comprehensive criteria for patients SBRT eligibility and dosimetric planning.