Abstract
BackgroundIn this study we have evaluated the accuracy of automatic, deformable structure propagation from planning CT and MR scans for daily online plan adaptation for MR linac (MRL) treatment, which is an important element to minimize re-planning time and reduce the risk of misrepresenting the target due to this time pressure.MethodsFor 12 high-risk prostate cancer patients treated to the prostate and pelvic lymph nodes, target structures and organs at risk were delineated on both planning MR and CT scans and propagated using deformable registration to three T2 weighted MR scans acquired during the treatment course. Generated structures were evaluated against manual delineations on the repeated scans using intra-observer variation obtained on the planning MR as ground truth.ResultsMR-to-MR propagated structures had significant less median surface distance and larger Dice similarity index compared to CT-MR propagation. The MR-MR propagation uncertainty was similar in magnitude to the intra-observer variation. Visual inspection of the deformed structures revealed that small anatomical differences between organs in source and destination image sets were generally well accounted for while large differences were not.ConclusionBoth CT and MR based propagations require manual editing, but the current results show that MR-to-MR propagated structures require fewer corrections for high risk prostate cancer patients treated at a high-field MRL.
Highlights
In this study we have evaluated the accuracy of automatic, deformable structure propagation from planning Computed tomography (CT) and magnetic resonance (MR) scans for daily online plan adaptation for MR linac (MRL) treatment, which is an important element to minimize re-planning time and reduce the risk of misrepresenting the target due to this time pressure
This study investigates the geometric accuracy of deformable image registration of target volumes and organs at risk (OAR) in high-risk prostate cancer patients for both CT-MR and MR-MR registrations using manual delineations as ground truth
Population median mean surface distance (MSD) values demonstrated better agreement with the ground truth for all deformed structures based on MR relative to CT (MR-MR values were 0.17–1.16 mm lower)
Summary
In this study we have evaluated the accuracy of automatic, deformable structure propagation from planning CT and MR scans for daily online plan adaptation for MR linac (MRL) treatment, which is an important element to minimize re-planning time and reduce the risk of misrepresenting the target due to this time pressure. Different commercial algorithms have been evaluated on different anatomies when performing DIR from CT to MR, showing great potential, and uncertainties in the deformations [13,14,15,16]. Use of MR-MR DIR in the online MRL treatment workflow, as described by Bertelsen et al [11], could provide more precisely propagated structures. To our knowledge, this has not yet been verified
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