3D aignment correction for proton beam treatment

The Bragg Peak of proton beams allows applying treatment doses onto carcinogen tissue with accuracy much below 1.0 mm and decreases the dose applied on surrounding tissue. The possible accuracy is limited by set-up errors from the initial patient alignment in respect of the particle beam nozzle. In this contribution a solution is presented, that allows overcoming these limitations. Two X-ray images acquired from within the treatment machine are compared to digitally reconstructed radiographs (DRRs) from a CT series. The system automatically determines initial set-up errors and computes a position correction in either 5 or 6 degrees of freedom (DoF). For 5 DoF we increase performance by reducing the number of DRRs that have to be rendered from the CT series by combining several 2D offset corrections. The DRRs are then iteratively adapted to the corrected 3D geometry. To achieve full 6 DoF alignment correction, the X-ray images are directly compared to respective DRRs for an assumed patient position and the image correlation is maximized to find the best fitting patient alignment.