Background and purpose: Optical surface imaging system is used in image-guided radiotherapy (IGRT). This study aimed to evaluate the clinical applicability of the Catalyst

TM

system and cone-beam computed tomography (CBCT) in tumor radiation therapy. Methods: Thirty-three patients with thorax tumor were fixed with suitable methods at Fudan University Shanghai Cancer Center. Catalyst

TM

system and CB

CT acquired the same time images. The images were aligned with simulation planning CT images. These aligned results for images in x

y and z directions for translation error and pitch (PIT)

roll (ROL) and rotation (RTN) directions for rotation error were obtained

and means

standard deviations

systemic error and random error were calculated. Paired samples t test was applied to evaluate the differences. Results: The setup errors of CBCT registration in x

y and z translational directions were (0.95±1.18) mm

(1.28±1.63) mm and (0.97±1.20) mm

respectively. The setup errors of CBCT registration in PIT

ROL and RTN rotational directions were (0.73±0.65)°

(1.07±0.86)° and (0.69±0.69)°

respectively. The setup errors of Catalyst

TM

registration in x

y and z translational directions were (0.96±1.35) mm

(1.43±1.66) mm and (1.59±1.98) mm

respectively. The setup errors of Catalyst

TM

registration in PIT

ROL and RTN rotational directions were (0.86±0.80)°

(0.87±0.74)° and (0.75±0.76)°

respectively. The differences in systemic error and random error between the two methods were less than 1 mm. Conclusion: There is no significant difference between the two approaches. Catalyst

TM

could be used as an alternative to CBCT.