Room: ePoster Forums
Purpose: To study the characteristics of the profile and angular information in (flattening filter free) profile using hough transform. This helps in beam steering since the shape is highly dependent on accurate beam steering. Now EPID, IC profiler steering is becoming familiar for accurate beam steering and the instantaneous information of shape of the profile is very much important.
Methods: True beam fff profiles are used for this process. Traditional methods only used phantom arrangement for extracting true beam profiles, which has pitfalls since time consuming and highly dependent on moving arm positioning. Using Hough transform at dmax mostly wide fields are used for this purpose. It can be visualized as three dimensionally cone on cuboid and two dimentionally isosceles triangle on rectangle. It has characteristics of vertical angle from rectangular base and isosceles angle from triangular base and curvature at the top can be extracted. The profile is continuously changes from arc to triangular structure with field size. The difference between two arms can be corrected using hough transform in order to achieve symmetry.
Results: The curvature can be fit with 3rd degree polynomial for lower field sizes to 5th degree polynomial for large field size with regression coefficient more than 0.99. Its double derivative is changes from straight line for less than 10*10 field sizes to polynomial for higher field size. The important aspect of hough transform is helpful to find the angle instantly by matlab code. It was found that the difference of isosceles angle varies upto 3 degrees and it can be automatically steered using ic profiler and EPID without loosing any profile information.
Conclusion: Automatic steering using hough transform can be installed in future in the system. It can be evaluated manually and ensures the profile characteristics within the limit.