Objective To propose a novel method for verifying the isocenter in radiotherapy based on markers and conduct a preliminary test. Methods A feasibility experiment was conducted on wooden box phantom for radiotherapy resetting. Fifteen groups of displacement data were randomly generated,corresponding to the position deviations of the isocenter in the radiotherapy plan relative to the original isocenter. According to each set of displacement data,with the aid of movable lasers and a CT scanning couch,CT scanning was performed with two sets of markers (3 per set) affixed to the phantom which were corresponding to the original and treatment isocenters,respectively. In the Eclipse treatment planning system,the coordinate data of the original and treatment isocenters were manually verified,and the difference of coordinate data was calculated to obtain the actual displacement value. The treatment isocenter position was finally confirmed by comparing with the actual displacement. In addition,the study attempts to use threshold segmentation algorithm to automatically detect metal markers and obtain coordinate values of the original isocenter on patient-positioned CT images. In the wooden box experiment,the absolute value of the difference between the actual displacement value and the planned displacement value (?d) was used to represent the position accuracy of treatment isocenter,and the deviation value obtained with threshold segmentation algorithm for isocenter detection was ?s. Results The ?d in the X (left-right),Y (superior-inferior) and Z (anterior-superior) directions was (0.83±0.37) mm,0 (0,0.5) mm and (0.45±0.29) mm,respectively. The ?s in the X,Y and Z directions was (0.46±0.22) mm,0 (0,0.5) mm and (0.33±0.29) mm,respectively. The mean values of ?s in 3 directions were all lower than 2 mm,within the range of permissible clinical positioning error. Conclusion The method of automatically verifying treatment isocenter position based on markers is feasible,and the study provides a useful reference for radiotherapy resetting using CT simulator.

Objective To propose a novel method for verifying the isocenter in radiotherapy based on markers and conduct a preliminary test. Methods A feasibility experiment was conducted on wooden box phantom for radiotherapy resetting. Fifteen groups of displacement data were randomly generated,corresponding to the position deviations of the isocenter in the radiotherapy plan relative to the original isocenter. According to each set of displacement data,with the aid of movable lasers and a CT scanning couch,CT scanning was performed with two sets of markers (3 per set) affixed to the phantom which were corresponding to the original and treatment isocenters,respectively. In the Eclipse treatment planning system,the coordinate data of the original and treatment isocenters were manually verified,and the difference of coordinate data was calculated to obtain the actual displacement value. The treatment isocenter position was finally confirmed by comparing with the actual displacement. In addition,the study attempts to use threshold segmentation algorithm to automatically detect metal markers and obtain coordinate values of the original isocenter on patient-positioned CT images. In the wooden box experiment,the absolute value of the difference between the actual displacement value and the planned displacement value (?d) was used to represent the position accuracy of treatment isocenter,and the deviation value obtained with threshold segmentation algorithm for isocenter detection was ?s. Results The ?d in the X (left-right),Y (superior-inferior) and Z (anterior-superior) directions was (0.83±0.37) mm,0 (0,0.5) mm and (0.45±0.29) mm,respectively. The ?s in the X,Y and Z directions was (0.46±0.22) mm,0 (0,0.5) mm and (0.33±0.29) mm,respectively. The mean values of ?s in 3 directions were all lower than 2 mm,within the range of permissible clinical positioning error. Conclusion The method of automatically verifying treatment isocenter position based on markers is feasible,and the study provides a useful reference for radiotherapy resetting using CT simulator.