Results of a single arm phase II clinical trial: online-adaptive stereotactic body radiotherapy of abdominal-pelvic oligometastases.

Abstract

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

Methods: Patients with oligometastatic A-P LN were enrolled and treated to a total dose of 45 Gy in five fractions on the CyberKnife. For each patient, a library of three plans was created using a pre-treatment diagnostic CT scan and the treatment planning CT scan. Following a decision tree, the radiotherapy technologist (RTT) selected the best plan of the day, i.e. the plan with the highest target coverage without exceeding OAR constraints. The primary endpoint was local control (LC), and secondary endpoints were toxicity and overall survival (OS).

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 16 patients (31%) had a different origin. After a median follow-up of 38.5 months, local control at one year was 96% and 80% at three years; 20 patients had died, resulting in a median OS of 4.1 years. No grade ≥ 4 toxicity was observed. One patient (2%) developed a grade 3 ureter stenosis.

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