Large-deformation image registration using fluid landmarks

For each patient receiving definitive treatment for cervix cancer, several CT/MR imaging studies need to be registered in order to specify the total physical or biological dose to each fixed tissue voxel in an organ system. This turns out to be a difficult problem due to large localized deformations and displacements of bladder, rectum, vagina, uterus and paracervical tissues due to tumor regression, bladder and rectal filling variations, and especially insertion of the applicator itself. This paper explores the utility of using the fluid landmark image registration method to register images before and after insertion of the brachytherapy applicator in order to track radiation dose from one treatment to the next.