Long-term results of dynamic tumor-tracking stereotactic body radiotherapy with real-time monitoring using a gimbal-mounted linac for liver tumors: a multicenter observational study.

Background: Despite advancements in liver tumor treatments, a persistent need remains for minimally invasive therapies with high efficacy and long-term outcomes. In a previous multicenter phase II study, the safety and efficacy of dynamic tumor-tracking stereotactic body radiotherapy with real-time monitoring of liver tumors were evaluated using a gimbal-mounted system. Herein, we report the updated long-term results of this technique.

Methods: This observational study examined patients with a single liver tumor, respiratory movement of at least 10 mm, performance status of 0-2, and Child-Pugh score of < 9. Patients who agreed to participate in the trial underwent dynamic tumor-tracking stereotactic body radiotherapy (prescribed dose, 40 Gy in five fractions for the planning target volume [D₉₅]; 70% of the maximum dose). The primary endpoint was the 4-year overall survival rate. Secondary endpoints included 4-year local control and progression-free survival rates and the incidence of adverse events.

Results: Between September 2015 and March 2019, 48 patients (median age, 74 years; median tumor diameter, 17.5 mm) underwent dynamic tumor-tracking stereotactic body radiotherapy. All lesions were successfully treated (hepatocellular carcinoma, 39 patients; liver metastases, 9 patients). The median observation period was 46 months, and the 4-year overall survival, local control, and progression-free survival rates were 67.4%, 97.9%, and 29.1%, respectively. Eight patients had grade 3 hepatobiliary enzyme elevation, hematologic toxicity, or hyponatremia; none had grade ≥ 4 adverse events.

Conclusion: These findings demonstrate the long-term safety and efficacy of dynamic tumor-tracking stereotactic body radiotherapy for liver tumors, with an excellent local control rate.