Fast and accurate deformable contour propagation for intra-fraction adaptive magnetic resonance-guided prostate radiotherapy.

To facilitate full intra-fraction adaptive MR-guided radiotherapy, accurate contour propagation is needed. We aimed to assess the clinical usability of intra-fraction propagated contours by a deformable image registration algorithm in ten prostate cancer patients. Two observers judged the contours on need for manual adaptation and feasibility of adapting contours within 3 min. CTV and bladder contours needed none or only minor editing in most cases (≥ 97%), whereas rectum contours needed more extensive editing in 12-23%. Nevertheless, adaptation times were < 3 min for ≥ 93% of the cases. This paves the way for exploring adaptive workflows using intra-fraction deformable contour propagation.