Results of a Single-Arm Phase 2 Clinical Trial: Online Adaptive Stereotactic Body Radiation Therapy for Abdominal-Pelvic Oligometastases

Abstract

Purpose: This study reports on the clinical outcomes of the single-arm phase-2 STEAL trial investigating online adaptive stereotactic body radiation therapy (SBRT) for abdominal-pelvic lymph node (A-P LN) oligometastases.

Methods and materials: Patients with oligometastatic A-P LN were enrolled and treated to a total dose of 45 Gy in 5 fractions on the CyberKnife. For each patient, a library of 3 plans was created using a pretreatment diagnostic computed tomography (CT) scan and the treatment planning CT scan. Following a decision tree, the radiation therapy technologist (RTT) selected the best plan of the day, ie, the plan with the highest target coverage without exceeding organs at risk constraints. The primary endpoint was local control (LC), and the secondary endpoints were toxicity and overall survival.

Results: In total, 52 patients were included, and 55 online adaptive treatments were performed. The primary tumor was prostate adenocarcinoma in 19 patients (37%), colorectal in 17 (33%), and had a different origin in 16 patients (31%). After a median follow-up of 38.5 months, LC at 1 year was 96% and 80% at 3 years; 20 patients had died, resulting in a median overall survival of 4.1 years. No grade ≥4 toxicity was observed. One patient (2%) developed a grade 3 ureteral stenosis.

Conclusions: CT-guided online adaptive SBRT for A-P LN oligometastases using an RTT-only library of plans strategy is feasible, safe, and resulted in an excellent LC with a low toxicity rate.