Dose monitoring in prostate cancer radiotherapy using CBCT to CT constrained elastic image registration

Abstract

The recent concept of Dose Guided Radiotherapy (DGRT) consists in computing a cumulative dose distribution at each treatment fraction to decide if a treatment replanning is necessary. These cumulative dose distributions are obtained by mapping the daily dose distributions with the results of a non-rigid registration between the planning CT scan and daily CBCT images. But, mainly because of large deformations and of the scatter effect of CBCT, the application of this methodology to prostate cancer radiotherapy is very challenging. In this paper, we adapt a nonparametric non-rigid registration algorithm based on Mutual Information to register the daily CBCT scan to the planning CT scan in the context of prostate cancer DGRT. In order to improve registration accuracy, we then propose a modification of the registration framework to introduce landmark constraints. We show that this constrained non-rigid registration algorithm was able to significantly increase the accuracy of the cumulative dose estimation. © 2011 Springer-Verlag.