Analysis of Surface Guidance Versus Laser Alignment for Precision Lung Cancer Particle Therapy

Introduction Lung particle therapy using pencil beam scanning achieves high dose conformity but remains vulnerable to geometric uncertainties from suboptimal initial setup. Surface-guided radiotherapy (SGRT) improves setup reproducibility in photon workflows, yet evidence in lung particle therapy remains limited. This study evaluates the clinical value of SGRT in improving six degrees of freedom (6-DOF) setup reproducibility in lung cancer particle therapy. Methods This retrospective cohort study analyzed 63 lung cancer patients receiving 1277 treatment fractions at our center from February 2023 to January 2024. Comparisons were made between conventional laser-based positioning, which included 983 fractions, and SGRT workflows, which included 294 fractions. Following patient positioning, therapists manually registered orthogonal kilovoltage (kV) x-ray images with planning digitally reconstructed radiographs (DRRs) to calculate 6-DOF correction parameters, including translational (lateral, longitudinal, vertical) and rotational (pitch, roll, yaw) components, and to quantify the pre-correction setup error . Absolute 6-DOF displacements and three-dimensional vector magnitudes (MAG) were measured. The analysis included 36 supine patients with 739 treatment fractions and 27 prone patients with 538 fractions. Results The SGRT group exhibited statistically significant reductions in median shifts for lateral (0.25 cm to 0.21 cm, p = 0.021), longitudinal (0.25 cm to 0.21 cm, p = 0.014), pitch (1.0° to 0.8°, p = 0.001), and MAG (0.59 cm to 0.53 cm, p = 0.002) compared to conventional methods. These improvements in median values were more pronounced in supine-positioned patients, while no significant differences were observed in prone-positioned patients. Furthermore, substantial reductions were achieved in ninth decile deviations (1.09 cm to 1.03 cm), and the third quartile deviations (0.83 cm to 0.74 cm) in the overall cohort. Conclusion SGRT enhances setup precision for proton and carbon ion lung cancer radiotherapy, reduces pre-correction setup error, and provides clinical support for patient setup reproducibility.