Research On In-situ Detection Method For Positioning Performance Of Auto-Scanning Water Phantom System

The positioning performance of auto-scanning water phantom system has an important impact on the measurement of water absorbed dose distribution of medical linear accelerator.In view of the current situation that the positioning performance of water phantom system can not be dectected portably in situ and the accuracy of threedimensional measurement method in multi-media can not meet the detection requirement,a portable detection method in situ based on laser tracker refraction compensation is proposed.The research work mainly includes the following parts:(1)The design of the in-situ detection scheme for positioning performance of water phantom system.The technical indicator of the detection method is proposed,the measurement process of the in-situ detection method with laser tracker is clarified,the device as a reference for the in-situ detection method is designed and built,and the software for positioning performance detection of water phantom system based on laser tracker is written.(2)The establishment and verification of the refraction compensation model in the in-situ detection method.According to the measurement principle of laser tracker and the measurement model in the water phantom system,the waterless and watery refraction compensation models are established respectively,and experiments are designed to verify the effectiveness of the waterless and watery refraction compensation models.(3)The detection experiment for positioning performance of water phantom system and measurement uncertainty evaluation.According to the planned movement path and the calculation method for evaluation parameters of positioning performance,the reference device detection,in-situ detection without water and in-situ detection with water for positioning performance of water phantom system are carried out respectively.The results showed that the positioning performance of waterless and watery detection in situ are basically consistent with the reference value,and water has no obvious effect on the positioning performance,and the single-axis positioning performance is better than the spatial positioning performance.In addition,the monocular photogrammetry method was used to verify that the weight of the target ball has no significant effect on the positioning performance.Finally,the method called Monte Carlo is used to evaluate uncertainty for the waterless and watery detection in situ.For the waterless detection in situ,the estimated value of measurement deviation is-0.020 mm,and the standard uncertainty is 0.012mm;for the watery detection in situ,the estimated value of measurement deviation is 0.023 mm,and the standard uncertainty is 0.032 mm,which meets the technical indicator.