A Method to Accurately Determine the Original Isocenter of
Radiotherapy According to the Structure of Marked Points
CHENG Long1a, SHI Feiyue1b, WANG Min1b, QIN Wei1b, WU Qianqian1a, JIANG Hongbing1a,2
1. a. Department of Medical Equipment; b. Radiation Therapy Center, Nanjing First Hospital, Nanjing Medical University,
Nanjing Jiangsu 210006, China; 2. Nanjing Emergency Medical Center, Nanjing Jiangsu 210003, China
Abstract：Objective To propose a method to accurately determine the original isocenter coordinates of radiotherapy based on the
structure of the marked points (marker structure method), and analyze the difference between it and the original isocenter determined
by the conventional method. Methods A total of 40 patients with thoracic and abdominal tumors who received radiotherapy
were selected. First, the menu tool of the Varian Eclipse treatment planning system was used to manually outline the structure of
the left, middle, and right three marked points on the patient’s CT image, and obtain the geometry of the marked point structure
center coordinates. Then the coordinates of the original isocenter were calculated according to the formula and compared with the
conventional method to analyze the values of the left and right direction difference ΔX, the abdominal-back direction difference ΔY,
the head and foot direction difference ΔZ, the total distance difference ΔS, and the horizontal tilt angle θ. Results Among the 40
patients, the number of marked points on the 1, 2, and 3 slice CT images were 11, 28, and 1, respectively. In the 17 cases where the
marked points incompletely appeared on the 2-slice CT image, the marked point structure method compared with the conventional
method, ΔX, ΔY, ΔZ and ΔS were (0.43±0.32), (0.51±0.29), (1.16±0.50), (1.43±0.43) mm, respectively; when 11 cases of
marked points appeared completely on the 2-slice CT image, the values of ΔZ and ΔS were (2.18±0.14) and (2.34±0.12) mm
respectively compared with the two methods, the mean value exceeded 2 mm (P<0.05), the difference was statistically significant.
For 40 patients, the horizontal tilt angle θ was 0.25°±0.17°. Conclusion The marked point structure method can accurately
determine the coordinate value of the original isocenter of radiotherapy. When the marked points appear on the multi-slice CT image,
it can effectively make up for the shortcomings of the conventional method.
程龙1a，时飞跃1b，王敏1b，秦伟1b，吴倩倩1a, 蒋红兵1a,2. 一种根据标记点结构精确确定放疗原始等中心的方法[J]. 中国医疗设备, 2022, 37(4): 90-93.
CHENG Long1a, SHI Feiyue1b, WANG Min1b, QIN Wei1b, WU Qianqian1a, JIANG Hongbing1a,2. A Method to Accurately Determine the Original Isocenter of
Radiotherapy According to the Structure of Marked Points. China Medical Devices, 2022, 37(4): 90-93.
