Multiregional assessment of surface guidance for patient positioning in radiotherapy

Accurate and reproducible patient positioning is critical in external beam radiotherapy to ensure optimal target coverage while sparing surrounding healthy tissue. This retrospective single-institution study compared surface-guided radiation therapy (SGRT) using the Catalyst™ HD system with conventional skin-marker (SKM) alignment in thoracic and pelvic treatments. Sixty patients (20 thoracic, 40 pelvic) and 1,105 treatment fractions were analyzed. Thoracic patients received both SGRT and SKM workflows sequentially, enabling paired analysis; pelvic patients were treated using either SGRT or SKM exclusively. Translational 3D offsets, verified by image guidance, were quantified from couch shift data, and setup precision was evaluated using descriptive statistics, hypothesis testing, and linear mixed-effects models. In thoracic treatments, SGRT reduced mean 3D offsets from 0.91 cm to 0.42 cm (52 % reduction) and variance from 0.54 cm² to 0.06 cm² (p < 0.001). Pelvic SGRT cases showed a 37 % reduction in mean 3D offsets (0.68 cm to 0.43 cm) and variance reduction from 0.18 cm² to 0.04 cm² (p < 0.001). The proportion of fractions within 5 mm increased from 25.0 % to 65.2 % (thorax) and from 37.0 % to 67.7 % (pelvis) with SGRT. Setup margins calculated using the van Herk formula decreased from 1.27 cm to 0.46 cm (thorax) and from 0.92 cm to 0.35 cm (pelvis). These findings demonstrate that SGRT improves setup accuracy and reproducibility across anatomical sites, enabling tighter setup margins and supporting workflow efficiency, without reducing verification imaging frequency in IGRT-based treatments. Routine integration of SGRT can therefore enhance setup accuracy, improve setup precision, and support efficient positioning workflows in modern radiotherapy.