Research On Quality Assurance Of Stereotactic Radiotherapy Based On CyberKnife System

Stereotactic radiation therapy is a precise radiotherapy technology which widely recognized in the clinic.It delivers a highly conformal,potent dose of radiation to the tumor in a limited number of fractions(1-5 fractions)while minimizing radiation damage to organs at risk.Cyber Knife is an image-guided stereotactic dose delivery system designed for both focal irradiation and radiation therapy that integrates multiple advanced image tracking technologies.The system uses Synchrony tracking technology,which can actively track the tumor and accurately estimate the motion pattern of the tumor,ensuring the dose escalation on tumor target area and protecting the normal tissues and organs around.In the light of this,Cyber Knife system has unique advantages especially in treating tumors involving breathing movement.Due to the precise tracking technology applied by Cyber Knife system and the characteristics of high radiation dose delivered by low segment of stereotactic radiotherapy,it is necessary to minimize the existence of errors to ensure the treatment effect and prevent radiotherapy accidents.Target motion may compromise the accuracy of stereotactic radiotherapy.In the first part of this study,we aim to estimate the intrafractional rigid motion of liver tumor based on real-time k V X-ray images acquired by Cyber Knife stereo imaging system.The results showed that The translational shifts of liver tumors in left-right(LR),anterior-posterior(AP),and superior-inferior(SI)directions were 2.92 ± 1.98 mm,5.54 ± 3.12 mm,and 16.22 ± 5.86 mm,respectively;the rotational angles in left-right(LR),anterior-posterior(AP),and superior-inferior(SI)directions were 3.95° ±3.08°,4.93° ±2.90°,and 4.09° ±1.99°,respectively.Rotational correction decreased 3D fiducial displacement from 1.19 ± 0.35 mm to 0.65 ±0.24 mm( < 0.01).The maximum translational movement occurred in the SI direction.Rotational correction decreased fiducial displacements and increased tumor tracking accuracy.The quality assurance(QA)of the Cyberknife system is also particularly important to improve the accuracy of radiotherapy.The AAPM TG 135 report shows that the daily quality assurance of the Cyber Knife system includes Automatic Quality Assurance(AQA)test.AQA test is a simple and fast method to measure the accuracy of the Cyber Knife robot arm and the stability of the whole system.The principle of this method is to place a radio-opaque metal sphere in the align center,and the accuracy of robot arm and the stability of Cyber Knife system can be analyzed by calculated the concentricity of the projection center of the horizontal and vertical beams on the film in the AQA mold and the tungsten ball center in the mold.However,in practice,it has been found that,for a film image with a malposition rotation angle of 3 ° or more during scanning,the traditional AQA film analysis software may result in an error or fail to identify the inner circle correctly.In the second part of this research,a new algorithm based on Hough transform is proposed for image analysis of Cyber Knife AQA test.This algorithm improves the stability of film analysis.