Dynamic tumor-tracking stereotactic body radiotherapy with real-time monitoring of liver tumors using a gimbal-mounted linac: A multi-institutional phase II study.

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This prospective multicenter phase II study aimed to evaluate the safety and efficacy of dynamic tumor tracking (DTT) stereotactic body radiotherapy (SBRT) with real-time monitoring of liver tumors using a gimbal-mounted system. Patients with<4 primary or metastatic liver tumors with diameters≤50mm and expected to have a respiratory motion of≥10mm were eligible. The prescribed dose was 40Gy in five fractions. The primary endpoint was local control (LC) at 2years. The secondary endpoints were overall survival (OS), progression-free survival (PFS), treatment-related toxicity, and tracking accuracy. Between September 2015 and March 2019, 48 patients (48 lesions) with a median age of 74years were enrolled from four institutions. Of these, 39 were diagnosed with hepatocellular carcinoma and nine with metastatic liver cancer. The median tumor diameter was 17.5mm. DTT-SBRT was successfully performed in all patients; the median treatment time was 28min/fraction. The median follow-up period was 36.5months. The 2-year LC, OS, and PFS rates were 98.0%, 88.8%, and 55.1%, respectively. Disease progression was observed in 33 (68.8%) patients. One patient (0.2%) had local recurrence, 31 (64.6%) developed new hepatic lesions outside the irradiation field, and nine (18.8%) had distant metastases (including overlap). Grade 3 late adverse events were observed in seven patients (14.5%). No grade 4 or 5 treatment-related toxicity was observed. The median tracking accuracy was 2.9mm. Employing DTT-SBRT to treat liver tumors results in excellent LC with acceptable adverse-event incidence.