Objective:To compare the positioning errors in tracing the body surface markers between radiotherapy placement with or without using the laser positioning coordination system in post-breast conservative surgery patients, and to verify the clinical value of the laser positioning coordination system.Methods:A total of 45 post-breast-conservative surgery patients who underwent radiotherapy in Department of Radiation Oncology of the Affiliated Hospital of Inner Mongolia Medical University from January 2022 to September 2023 were prospectively collected. In the experimental group 1 ( n=15), the initial version of the laser positioning coordination system was employed to trace the body surface markers. In the experimental group 2 ( n=15), the upgraded version of the laser positioning coordination system was adopted to draw the body surface markers. In the control group ( n=15), the body surface markers were traced with conventional approach. All patients were treated with spiral tomotherapy (TOMO), and the error values in the left and right directions ( X), head and foot directions ( Y), ventral and dorsal directions ( Z), and rotation angles (ROLL) before each radiotherapy were recorded. The differences in the positioning errors among the three groups were analyzed by t-test. Results:The positioning errors in the X, Y, Z directions and ROLL in the experimental group 1 were (3.10±2.43) mm, (4.36±3.45) mm, (2.29±2.49) mm and 0.95°±0.88°, and (2.88±2.28) mm, (3.58±2.95) mm, (2.40±2.54) mm, and 0.70°±0.70° in the experimental group 2, and (4.32±3.48) mm, (5.49±4.74) mm, (2.61±3.38) mm and 1.22°±1.16° in the control group, respectively. Statistical significance was observed in the differences of positioning errors in the X, Y directions and ROLL between the experimental group 1 and control group ( t=4.32, 2.89, 2.78, P < 0.001, =0.004, =0.006), respectively. Statistical significance was detected in the differences of positioning errors in the X, Y directions and ROLL between the experimental group 2 and control group ( t=5.20, 5.14, 5.82, all P<0.001). Statistical significance was noted in the differences of positioning errors in the Y direction and ROLL between the experimental group 1 and 2 ( t=2.58, 3.41, P=0.010, 0.001). Conclusion:The laser positioning coordination system-assisted tracing the body surface marking line can significantly reduce the positioning errors in the X and Y directions and ROLL, and the upgraded version of the laser positioning coordination system can further reduce the positioning errors in the Y direction and ROLL compared with the initial version, which is of high clinical application value.