Research On Detection Accelerator Isocenters By Various Fitting Algorithms

In today's increasingly severe cancers,the use of medical accelerators for radiotherapy has become a key technology for the treatment of tumors,and the precision of the isocenter of medical linear accelerators directly affects the target area and the location of endangered organs as defined in the treatment plan.The modern medical linear accelerator is designed according to the isocenter principle.The rotation axis of the frame and the rotation axis of the treatment bed intersect at one point.This point is the isocenter of the medical linear accelerator.At present,when the isocenter is calculated by using the positioning spheres that can be recognized by the infrared positioning system to perform the trajectory fitting on the accelerator and the treatment bed,the rotation trajectory of the positioning ball on the treatment bed and the head is directly viewed as a spherical space.The point is fitted and the reference axis is obtained by calculating the center of the sphere and the normal vector of the circle plane.However,the space circle obtained by this method is not a large circle of the spherical shell.After solving the spherical center coordinates,it is likely to be far from the actual circle plane and cause errors.In this paper,this method is improved.Firstly,the space plane where the motion trajectory is located is fitted,and then the space sphere shell is fitted under the constraint that the sphere center coordinate is within the fitting plane,and the obtained sphere center coordinate is the space circle.The coordinates of the center of the circle.This paper also makes full use of the geometrical characteristics and mathematical theorem of the space circle,and establishes a mathematical calculation model based on the middle-vertical surface and space vector ideas.The calculation equation of the center of the circle is derived based on the indirect adjustment with a constraint condition.In order to verify the influence of different fitting algorithms on the error of the isocenter,a series of experiments are designed.Experiments show that the method of intersecting mid-vertical surfaces with round winding is better than other algorithms and has high precision and real-time performance.Because hospital Medical accelerator and treatment beds cannot rotate 360 degrees,and some treatment rooms have limited space,the distance between the infrared positioning device and the accelerator is insufficient to allow the infrared positioning device to monitor the accelerator movement to every angular position.Three sampling methods were used to measure the sampling points at different angles.It was found that after the rotation angle is less than a certain angle,the calculation error of the isocenter can no longer meet the requirements of precision radiotherapy.In the problem of fitting small arcs with small angles,this paper also adopts a high-density sampling method to improve the accuracy of the isocenters under short circular arcs,making it possible for accelerators to be fit-calculated when rotated only 20 degrees.Accuracy is less than 1mm accuracy error required by precision radiotherapy in national standards.Finally,through the method proposed in this paper,the actual mechanical center of the accelerator is measured in the hospital.Through this point as a standard,the physicist of the radiology department is assisted in the verification and adjustment of the accelerator center,the quality control level of the accelerator machinery is improved,and the radiation is improved.The quality of treatment provides stronger protection.