Adrenal Stereotactic Body Radiation Therapy in the Management of Oligometastatic Lung Cancer: Patient Selection Matters

Purpose: Adrenal metastases are commonly identified in the context of primary lung cancer. Recent literature has shown stereotactic body radiation therapy (SBRT) to improve progression free survival (PFS) in the setting of oligometastatic disease. Multiple studies have shown the efficacy and safety of adrenal SBRT. However, patient selection criteria are not well defined. We investigated the various patient selection criteria for adrenal SBRT and their associations with PFS.

Methodology: We examined a cohort of patients with stage IV oligometastatic primary lung cancer with adrenal metastases who were consecutively treated with 5-fraction SBRT (n=19). Multiple characteristics were selected for examination prior to data collection and PFS calculation. We considered 1) age 2) performance status 3) size greater than 4cm 4) presence of other metastases at adrenal metastasis diagnosis 5) presence of brain metastases at adrenal metastasis diagnosis 6) time to adrenal metastasis progression from primary diagnoses.

Results: Eighteen patients completed their treatments of 5-fraction adrenal SBRT with a median dose of 4500cGy (range from 3500cGy to 500cGy). One patient had a course of SBRT to each adrenal gland. Completion rate was 100% and there was no grade two or higher acute toxicities. Small bowel 0.03cc max dose ranged from 230cGy to 3410cGy with a median dose of 2350cGy. Median PFS was 4.7 months. PFS was the same for patients with and without brain metastases at adrenal progression (p=0.133). There were also no significant differences found in PFS when observing patients with adrenal progression within one year and greater than one year of initial diagnosis (p=0.474). Similarly, PFS did not change when comparing patients with adrenal lesions greater than 4cm to patients with adrenal lesion less than or equal to 4cm (p=0.477). PFS trended towards significance for patients older than 70 compared to patients who were 70 or younger (6.6 months vs 12.4 months, p=0.09). Additionally, PFS was significant for patients with ECOG 2 or higher compared to patients with ECOG less than 2 (1.4 months vs 11.5 months, p=0.027). Patients without additional metastatic disease at the time of progression had better PFS than patients with additional metastatic disease (18 months vs 7 months, p=0.016).

Conclusions: Patients with an ECOG score of 0 or 1 who did not have additional metastases at the time of adrenal metastasis exhibited a higher progression free survival rate after adrenal SBRT. Despite the small sample size, this study showed that appropriate patient selection for adrenal SBRT can lead to good long-term progression free survival with very minimal toxicity if any.

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