Impact of surface-guided prepositioning and respiratory coaching on the target localization accuracy in lung stereotactic body radiation therapy

This study assessed the effect of surface-guided radiation therapy (SGRT)-based prepositioning and respiratory coaching on target localization accuracy in lung stereotactic body radiation therapy (SBRT) using deep inspiration breath-holding. Thirty-five patients treated with lung SBRT (September 2022 to March 2025) were classified into three groups: Group A, VOXELAN prepositioning with reproducible respiratory control (≥ 60% setup criteria satisfied); Group B, VOXELAN prepositioning without reproducible control; and Group C, no VOXELAN prepositioning. Cone-beam computed tomography (CBCT) after prepositioning was used to retrospectively assess target localization. The concordance between the VOXELAN setup criteria and CBCT errors (> 5 mm) was analyzed using Fisher's exact test. Positional deviations and rotations were compared among groups using analysis of variance and post-hoc tests. Satisfying the VOXELAN setup criteria significantly correlated with CBCT localization within 5 mm (p = 0.0027). Vertical errors were smaller in Groups A and B than in Group C (p < 0.01), and lateral errors were smaller in Groups A and B than in Group C (p = 0.01 and p < 0.01, respectively). Rotational errors were within ± 1° in all groups, with a significant difference between Groups A and C (p < 0.02). Longitudinal errors were not significantly different between the groups. SGRT-based prepositioning with respiratory coaching improved setup reproducibility and correlation with the internal target position, particularly in the vertical, lateral, and rotational axes. Longitudinal accuracy remained limited, suggesting caution in margin reduction.