Surface-guided radiotherapy reduces residual setup errors in abdominal and pelvic radiotherapy

Abstract Introduction Achieving high setup accuracy is critical in modern radiotherapy, particularly with advanced techniques such as IMRT and VMAT. Surface-Guided Radiotherapy (SGRT) has been introduced to assist patient positioning and enhance setup reproducibility. This study aimed to compare residual setup errors between the conventional skin mark–based method and the SGRT-assisted technique in patients undergoing abdominal and pelvic radiotherapy. Methodology Fifty-five fractions from 17 patients with abdominal and pelvic cancers were retrospectively analyzed. The Catalyst™ SGRT system was utilized to reconstruct the three-dimensional surface using optical cameras. Setup performance was compared between the skin mark method (SM) and the skin mark combined with SGRT method (SM+SG). Residual setup errors were verified using CBCT. Translational shifts derived from CBCT were recorded to analyze interfraction setup uncertainties. Statistical analysis was performed using the Wilcoxon signed-rank test (p < 0.05) Results The median differences in residual setup errors between SM and SM+SG were statistically significant across all axes: 1.794 mm in the Lat. (1.273–2.290 mm, p < 0.0001), 2.519 mm in the Lng. (1.565–3.535 mm, p = 0.001), and 1.876 mm in the Vert. (0.774–2.867 mm, p = 0.003). The SM+SG method significantly reduced setup errors compared with SM in all directions. Conclusion SGRT significantly improves setup accuracy for abdominal and pelvic radiotherapy compared with skin mark–based setup, particularly in settings where daily CBCT is not available. Daily SGRT may therefore serve as an effective clinical alternative to skin mark–based setup, enabling more precise treatment delivery.