Interfraction movement and clinical outcome of immobilization for thoracic irradiation: A randomized controlled trial

Objective: To evaluate the impact of immobilization on set-up errors and clinical outcomes in patients receiving radiation therapy to the thorax. Methods: Patients receiving curative intent radiation therapy to the lung and esophagus were randomized to no immobilization (control) or immobilization (chest jig or vacuum bag), and treatment verification images were acquired within 3 days of commencing treatment and then weekly. The primary outcome was the proportion of patients having a deviation >5 mm from the isocenter. Assessment was carried out blinded to immobilization assignment. Results: Of the 77 patients, 75 patients were allocated to either immobilization or control. No statistical difference in the proportion of patients with bony displacements >5 mm from the isocenter were observed (P = 0.5), as was the case for both systematic and random errors between the groups. There was an increased risk of local failure in the immobilized control group (HR 1.46, 95% CI 0.78–2.71, P = 0.23) based on a competing risk analysis. The median overall survival was 18.4 months and 27.0 months in the control and immobilized groups, respectively (HR 0.73, 95% CI 0.51–1.04, P = 0.08). Conclusions: The results failed to show benefit with immobilization in reducing set-up errors, local control, and overall survival.