3404 - 10-year Experience of Ultra-Hypofractionated SBRT for Adrenal Metastases

Purpose/Objective(s):

Stereotactic Body Radiotherapy (SBRT) is an established modality for treating adrenal metastases, however there is limited evidence on treatment with fewer than 3 fractions. We describe outcomes for single and three fraction SBRT from our institution for adrenal metastases.

Materials/Methods:

A retrospective review was conducted on adrenal SBRT patients treated between January 2013 and March 2024 with 1-3 fractions. Toxicity was assessed using the Common Terminology Criteria for Adverse Events version 5.0. Survival and local control (LC) were assessed via Kaplan-Meier analysis. Prognostic factors were evaluated using a Cox proportional hazards model.

Results:

Among 64 patients, there were 70 treated lesions. Ninety percent of patients with documentation of performance status were ECOG 0-1. The median follow-up was 3.1 years and median overall survival was 2.4 years. Most lesions were treated with 26 Gy in 1 Fr (64%) or 42 Gy in 3 Fr (24%). The remainder (12%) were treated with either 18 Gy or 20 Gy in 1 Fr. Non-small cell lung cancer (44%), renal cell carcinoma (20%), and melanoma (19%) were the most common histologies.

LC for all patients at 1 and 2 years was 91% (95% CI 84%-99%) and 77% (95% CI 67%-90%). The 1 and 2 year LC for single-fraction treatment was 88% (95% CI 79%-99%) and 76% (95% CI 63%-91%), and for 3-fraction treatment was 100% and 82% (95% CI 62%-100%), respectively. No significant difference in local failure risk was observed between single and 3 fraction treatment. Induced oligometastatic state (HR 3.9, 95% C.I. 1.02-15.0, p=0.046) and receipt of prior chemotherapy (HR 3.6, 95% C.I. 1.1-11.4, p=0.03) were associated with a greater hazard for local failure. For those treated with 26 Gy in 1 Fr, higher planning target volume (PTV) D2% (HR = 2.8 per Gy, 95% C.I. 1.2-6.3, p=0.01) was associated with poorer local control. PTV volume and PTV D99% did not predict failure within the 26 Gy in 1 Fr or the 42 Gy in 3 Fr treatment groups.

Adrenal insufficiency occurred in 12.5% of patients, mostly in those with bilateral treatment. Only 3% of unilateral cases required adrenal replacement. Grade 1-2 toxicity occurred in 33% of patients, grade 3 toxicity in 3% of patients, and one patient experienced a duodenal perforation of at least grade 3 severity after receiving 26 Gy in 1 Fr. A review of the treatment volumes demonstrated the duodenum to have been under-contoured adjacent to the high dose region. A retrospective re-contouring of the duodenum demonstrated a duodenal maximum dose of 25.3 Gy, with a 3 mm planning at risk volume (PRV) maximum dose of 28.6 Gy.

Conclusion:

This study supports the efficacy of single or three fraction treatment for adrenal metastases. Our series demonstrated a single duodenal perforation which occurred in a patient with inadequate organ at risk voluming. Our findings emphasize the importance of diligence with organ at risk volumes with hypofractionated treatments.