Anatomically-adaptive multi-modal image registration for image-guided external-beam radiotherapy

Abstract

Image-guided radiotherapy (IGRT) allows observation of the location and shape of the tumor and organs-at-risk (OAR) over the course of a radiation cancer treatment. Such information may in turn be used for reducing geometric uncertainties during therapeutic planning, dose delivery and response assessment. However, given the multiple imaging modalities and/or contrasts potentially included within the imaging protocol over the course of the treatment, the current manual approach to determining tissue displacement may become time-consuming and error prone. In this context, variational multi-modal deformable image registration (DIR) algorithms allow automatic estimation of tumor and OAR deformations across the acquired images. In addition, they require short computational times and a low number of input parameters, which is particularly beneficial for online adaptive applications, which require on-the-fly adaptions with the patient on the treatment table. However, the majority of such DIR algorithms assume that all structures across the entire field-of-view (FOV) undergo a similar deformation pattern. Given that various anatomical structures may behave considerably different, this may lead to the estimation of anatomically implausible deformations at some locations, thus limiting their validity. Therefore, in this paper we propose an anatomically-adaptive variational multi-modal DIR algorithm, which employs a regionalized registration model in accordance with the local underlying anatomy. The algorithm was compared against two existing methods which employ global assumptions on the estimated deformations patterns. Compared to the existing approaches, the proposed method has demonstrated an improved anatomical plausibility of the estimated deformations over the entire FOV as well as displaying overall higher accuracy. Moreover, despite the more complex registration model, the proposed approach is very fast and thus suitable for online scenarios. Therefore, future adaptive IGRT workflows may benefit from an anatomically-adaptive registration model for precise contour propagation and dose accumulation, in areas showcasing considerable variations in anatomical properties.

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

“…For workflows using repetitive MR imaging, deformable image registration (DIR), contour propagation, and re-planning to be clinically feasible, a fast and accurate auto-contouring solution is needed that reduces the need for manual adaptation and that limits operator interaction [18] . The aim of this study was to explore the clinical quality of intra-fraction propagated contours produced by a DIR algorithm with respect to need for manual editing and feasibility of editing contours within a short time frame to allow for a fast, online-adaptive workflow for MR-guided PCa radiotherapy.…”

Interrater agreement of contouring of the neurovascular bundles and internal pudendal arteries in neurovascular-sparing magnetic resonance-guided radiotherapy for localized prostate cancer

“…Furthermore, the recent development of magnetic resonance-guided adaptive radiotherapy (MRgRT) has enabled real-time high-resolution MRI imaging during dose delivery and facilitates correction for both inter- and intra-fraction movement and tissue deformations [9] . Planning target volumes (PTV) can therefore be smaller as safety margins are reduced [10] . These improvements in treatment conformity using MRgRT facilitate neurovascular-sparing radiotherapy and could potentially improve sexual function outcomes in patients treated for localized PCa.…”

Adaptive magnetic resonance-guided neurovascular-sparing radiotherapy for preservation of erectile function in prostate cancer patients

“…MR imaging prior to and during dose delivery facilitates correction for interfraction motion and tissue deformations. Within the near future fast auto contouring and planning will provide a way to deal with intrafraction motion, thus allowing for further margin reduction and reduction of dose to organs at risk (OAR) [8,9]. To date, no study has examined the planning feasibility of neurovascular-sparing MRgRT for localized PCa.…”