Geodesic Registration for Cervical Cancer Radiotherapy

Uterus, bladder and rectum are the maximally exposed organs during cervical cancer radiotherapy and are at high risk of radiation exposure. Estimation of dose accumulation in these organs across multiple fractions of external beam radiotherapy (EBRT) and brachytherapy (BT) is extremely challenging due to structural mis-correspondences and complex anatomical deformations between the EBRT and BT images. This paper proposes a unified registration framework that aligns multiple EBRT and BT images of a patient to a single coordinate frame for a cumulative dose assessment. The proposed method transforms the radiotherapy anatomical images to their distance maps from the critical organs (uterus, bladder, and rectum) and registers the distance maps. A Markov random field model is used to fuse the resulting dense deformations and transform the anatomical image. Registration accuracy is evaluated on 42 clinical image pairs and it is shown that the proposed system outperforms existing methods in the literature.