Objective:To analyze the positioning error and the overall setup errors (OSEs) of patients undergoing gamma knife pain-free face mask fractionated treatment for head tumors based on kV orthogonal image guidance.Methods:A total of 58 patients who received image-guided fractionated gamma knife treatment for head tumors with a pain-free face mask at the Gamma Knife Treatment Center of Xi'an International Medical Center Hospital from July 1, 2022 to May 31, 2024 were included in the study. A kV-class orthogonal X-ray IGPS image-guided positioning system was used to collect positioning errors in three translational directions: left-right (X), anterior-posterior (Y), and head-foot (Z), as well as in three rotational directions: left-right (P), anterior-posterior (R), and head-foot ( Y) before correction. After online correction and combined with manual positioning verification, the corrected positioning errors were recalculated. The OSEs in translational and rotational directions were calculated before and after correction. The positioning errors in all six directions (X, Y, Z, P, R, Y) before and after correction were plotted. And the OSE scatter plots in translational and rotational directions were created accordingly. Errors in the six directions and OSEs in translational and rotational directions were compared. The OSEs in translational and rotational directions were analyzed across different age groups and genders. Results:The pre-correction positioning errors in the X, Y, Z, P, R, Y directions for patients were (0.45±1.54) mm, -0.96 (-1.70, -0.28) mm, 1.67 (-0.15, 3.07) mm, (0.70±1.60) °, 0.65 (0.30, 1.19) °, (0.59±0.87) °, and the post-correction positioning errors were (-0.02±0.18) mm, 0.15 (0.10, 0.21) mm, 0.06 (-0.04, 0.16) mm, (0.20±0.79) °, 0.42 (0.19, 0.78) °, (0.20±0.63) °. There were statistically significant differences between before and after correction ( t=2.30, P=0.025; Z=-5.43, P<0.001; Z=-4.10, P<0.001; t=2.56, P=0.013; Z=-3.21, P=0.001; t=3.21, P=0.002). The OSEs in translational (X, Y, Z) and rotational (P, R, Y) directions before correction were 3.07 (1.93, 4.35) mm, 1.90 (1.28, 2.66) °, and the OSEs after correction were 0.27 (0.21, 0.33) mm, 1.08 (0.70, 1.54) °, with statistically significant differences ( Z=-6.60, P<0.001; Z=-5.52, P<0.001). For patients aged 18-44 years, the OSEs in translational (X, Y, Z) and rotational (P, R, Y) directions before and after correction were 3.65 (1.62, 3.95), 0.21 (0.21, 0.31) mm, 3.25 (2.24, 3.96) °, 0.92 (0.59, 1.45) °; for patients aged 45-59 years, the OSEs were 3.57 (2.17, 5.22), 0.29 (0.22, 0.35) mm, 1.89 (1.30, 2.30) °, 1.08 (0.62, 1.51) °; for patients aged 60-74 years, the OSEs were 2.92 (1.74, 4.06), 0.24 (0.19, 0.35) mm, 2.16 (1.09, 2.95) °, 0.98 (0.78, 1.75) °; for patients aged 75-89 years, the OSEs were 3.24 (2.12, 4.37), 0.29 (0.22, 0.47) mm, 1.73 (1.01, 1.83) °, 0.60 (0.47, 1.51) °. There were no statistically significant differences in OSEs of translational and rotational directions before and after correction among the four age groups ( H=1.23, P=0.747; H=1.74, P=0.627; H=7.45, P=0.059; H=2.80, P=0.424). For male patients, the OSEs before and after correction in translational (X, Y, Z) and rotational (P, R, Y) directions were (3.19±1.59), 0.27 (0.27, 0.33) mm, 1.89 (1.27, 2.75) °, (0.84±0.59) °; for female patients, the OSEs were (3.22±1.99), 0.26 (0.25, 0.35) mm, 1.90 (1.34, 2.41) °, (1.04±0.46) °. There were no statistically significant differences in OSEs of translational and rotational directions before and after correction between genders ( t=-0.07, P=0.949; Z=-0.48, P=0.632; Z=-0.02, P=0.161; t=-2.80, P=0.424) . Conclusions:The image-guided system, which is based on the kV orthogonal X-ray stereoscopic imaging, can significantly reduce the positioning errors between fractions of pain-free face mask gamma knife treatment for head tumor patients and improve the positioning accuracy of the gamma knife through the dual verification process of "automatic correction and manual review".