Abstract
BackgroundRetrospective studies on MRI-only radiotherapy have been presented. Widespread clinical implementations of MRI-only workflows are however limited by the absence of guidelines. The MR-PROTECT trial presents an MRI-only radiotherapy workflow for prostate cancer using a new single sequence strategy. The workflow incorporated the commercial synthetic CT (sCT) generation software MriPlanner™ (Spectronic Medical, Helsingborg, Sweden). Feasibility of the workflow and limits for acceptance criteria were investigated for the suggested workflow with the aim to facilitate future clinical implementations.MethodsAn MRI-only workflow including imaging, post imaging tasks, treatment plan creation, quality assurance and treatment delivery was created with questionnaires. All tasks were performed in a single MR-sequence geometry, eliminating image registrations. Prospective CT-quality assurance (QA) was performed prior treatment comparing the PTV mean dose between sCT and CT dose-distributions. Retrospective analysis of the MRI-only gold fiducial marker (GFM) identification, DVH- analysis, gamma evaluation and patient set-up verification using GFMs and cone beam CT were performed.ResultsAn MRI-only treatment was delivered to 39 out of 40 patients. The excluded patient was too large for the predefined imaging field-of-view. All tasks could successfully be performed for the treated patients. There was a maximum deviation of 1.2% in PTV mean dose was seen in the prospective CT-QA. Retrospective analysis showed a maximum deviation below 2% in the DVH-analysis after correction for rectal gas and gamma pass-rates above 98%. MRI-only patient set-up deviation was below 2 mm for all but one investigated case and a maximum of 2.2 mm deviation in the GFM-identification compared to CT.ConclusionsThe MR-PROTECT trial shows the feasibility of an MRI-only prostate radiotherapy workflow. A major advantage with the presented workflow is the incorporation of a sCT-generation method with multi-vendor capability. The presented single sequence approach are easily adapted by other clinics and the general implementation procedure can be replicated. The dose deviation and the gamma pass-rate acceptance criteria earlier suggested was achievable, and these limits can thereby be confirmed. GFM-identification acceptance criteria are depending on the choice of identification method and slice thickness. Patient positioning strategies needs further investigations to establish acceptance criteria.
Highlights
Retrospective studies on MRI-only radiotherapy have been presented
The Magnetic Resonance (MR)-PROTECT trial shows the feasibility of an MRI-only prostate radiotherapy workflow
This was detected after the MR-scan was completed and caused lack of signal in the peripheral parts of the body contour
Summary
Retrospective studies on MRI-only radiotherapy have been presented. Widespread clinical implementations of MRI-only workflows are limited by the absence of guidelines. The improvement of future prostate EBRT regimens will most likely involve decreased number of treatment fractions with higher fractionation dose [8, 9] as well as steeper dose gradients between the target and organs at risk (OAR) [10]. This introduces the need for a more accurate dose delivery, without potential risk of image registration uncertainties. A workflow with one image modality for both treatment planning and target delineation is needed This will reduce potential registration uncertainties and facilitate a more streamlined workflow for both patient and clinic. MRimaging (MRI) makes an ideal foundation for this singlemodality workflow – often referred to as MRI-only radiotherapy (RT) [11]
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