Development of a 3D remote dosimetry protocol compatible with <scp>MR</scp>g<scp>IMRT</scp>

Mein, Stewart; Rankine, L; Adamovics, J; Li, Harold; Oldham, Mark

doi:10.1002/mp.12565

Cited by 13 publications

(13 citation statements)

References 22 publications

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“…Overall, 3D dosimeters for dose response in a magnetic field exhibited a maximum difference of 1.6% in a comparison study [129]. The degradation of plastic 3D dosimeters over time was also quantified, reporting changes in optical density of around 5% per day, which did not impact on IMRT verification relying on AAPM TG 119 [130,131]. Also, Cherenkov imaging has been tested to acquire highresolution real-time dosimetric data, though limited to a 2D projection of the 3D dose cube [132].…”

Section: Dose Measurementsmentioning

confidence: 96%

Medical physics challenges in clinical MR-guided radiotherapy

et al. 2020

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The integration of magnetic resonance imaging (MRI) for guidance in external beam radiotherapy has faced significant research and development efforts in recent years. The current availability of linear accelerators with an embedded MRI unit, providing volumetric imaging at excellent soft tissue contrast, is expected to provide novel possibilities in the implementation of image-guided adaptive radiotherapy (IGART) protocols. This study reviews open medical physics issues in MR-guided radiotherapy (MRgRT) implementation, with a focus on current approaches and on the potential for innovation in IGART. Daily imaging in MRgRT provides the ability to visualize the static anatomy, to capture internal tumor motion and to extract quantitative image features for treatment verification and monitoring. Those capabilities enable the use of treatment adaptation, with potential benefits in terms of personalized medicine. The use of online MRI requires dedicated efforts to perform accurate dose measurements and calculations, due to the presence of magnetic fields. Likewise, MRgRT requires dedicated quality assurance (QA) protocols for safe clinical implementation. Reaction to anatomical changes in MRgRT, as visualized on daily images, demands for treatment adaptation concepts, with stringent requirements in terms of fast and accurate validation before the treatment fraction can be delivered. This entails specific challenges in terms of treatment workflow optimization, QA, and verification of the expected delivered dose while the patient is in treatment position. Those challenges require specialized medical physics developments towards the aim of fully exploiting MRI capabilities. Conversely, the use of MRgRT allows for higher confidence in tumor targeting and organs-at-risk (OAR) sparing. The systematic use of MRgRT brings the possibility of leveraging IGART methods for the optimization of tumor targeting and quantitative treatment verification. Although several challenges exist, the intrinsic benefits of MRgRT will provide a deeper understanding of dose delivery effects on an individual basis, with the potential for further treatment personalization.

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Section: Dose Measurementsmentioning

confidence: 96%

Medical physics challenges in clinical MR-guided radiotherapy

et al. 2020

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“…The MRIdian ® technology, which was used in this study, combines 0.35 T MRI with a multileaf-collimator linac and has already been described in detail before [9,[33][34][35]. Furthermore, various methods and procedures for quality assurance of the system are meanwhile also well established [31,[36][37][38].…”

Section: Dose Parametersmentioning

confidence: 99%

Head and neck radiotherapy on the MR linac: a multicenter planning challenge amongst MRIdian platform users

et al. 2021

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Purpose Purpose of this study is to evaluate plan quality on the MRIdian (Viewray Inc., Oakwood Village, OH, USA) system for head and neck cancer (HNC) through comparison of planning approaches of several centers. Methods A total of 14 planners using the MRIdian planning system participated in this treatment challenge, centrally organized by ViewRay, for one contoured case of oropharyngeal carcinoma with standard constraints for organs at risk (OAR). Homogeneity, conformity, sparing of OARs, and other parameters were evaluated according to The International Commission on Radiation Units and Measurements (ICRU) recommendations anonymously, and then compared between centers. Differences amongst centers were assessed by means of Wilcoxon test. Each plan had to fulfil hard constraints based on dose–volume histogram (DVH) parameters and delivery time. A plan quality metric (PQM) was evaluated. The PQM was defined as the sum of 16 submetrics characterizing different DVH goals. Results For most dose parameters the median score of all centers was higher than the threshold that results in an ideal score. Six participants achieved the maximum number of points for the OAR dose parameters, and none had an unacceptable performance on any of the metrics. Each planner was able to achieve all the requirements except for one which exceeded delivery time. The number of segments correlated to improved PQM and inversely correlated to brainstem D0.1cc and to Planning Target Volume1 (PTV) D0.1cc. Total planning experience inversely correlated to spinal canal dose. Conclusion Magnetic Resonance Image (MRI) linac-based planning for HNC is already feasible with good quality. Generally, an increased number of segments and increasing planning experience are able to provide better results regarding planning quality without significantly prolonging overall treatment time.

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“… 13 , 14 , 15 , 16 , 17 Furthermore, several studies have reported that polymer gels can be potentially used for 3D dosimetry especially for MRgRT. 18 , 19 , 20 , 21 …”

Section: Introductionmentioning

confidence: 99%

3D star shot analysis using MAGAT gel dosimeter for integrated imaging and radiation isocenter verification of MR‐Linac system

Kim

Shin

et al. 2022

J Applied Clin Med Phys

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This study aims to investigate a star shot analysis using a threedimensional (3D) gel dosimeter for the imaging and radiation isocenter verification of a magnetic resonance linear accelerator (MR-Linac). Methods: A mixture of methacrylic acid, gelatin, and tetrakis (hydroxymethyl) phosphonium chloride, called MAGAT gel, was fabricated. One MAGAT gel for each Linac and MR-Linac was irradiated under six gantry angles. A 6 MV photon beam of Linac and a 6 MV flattening filter free beam of MR-Linac were delivered to two MAGAT gels and EBT3 films. MR images were acquired by MR-Linac with a clinical sequence (i.e., TrueFISP). The 3D star shot analysis for seven consecutive slices of the MR images with TrueFISP was performed. The 2D star shot analysis for the central plane of the gel was compared to the results from the EBT3 films. The radius of isocircle (IC r ) and the distance between the center of the circle and the center marked on the image (IC d ) were evaluated. Results: For MR-Linac with MAGAT gel measurements, IC d at the central plane was 0.46 mm for TrueFISP. Compared to EBT3 film measurements, the differences in IC d and IC r for both Linac and MR-Linac were within 0.11 and 0.13 mm, respectively. For the 3D analysis, seven consecutive slices of TrueFISP images were analyzed and the maximum radii of isocircles (IC r_max ) were 0.18 mm for Linac and 0.73 mm for MR-Linac. The tilting angles of radiation axis were 0.31 • for Linac and 0.10 • for MR-Linac. Conclusion:The accuracy of 3D star shot analysis using MAGAT gel was comparable to that of EBT3 film, having a capability for integrated analysis for imaging isocenter and radiation isocenter.3D star shot analysis using MAGAT gel can provide 3D information of radiation isocenter, suggesting a quantitative extent of gantry-tilting.

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Development of a 3D remote dosimetry protocol compatible with MRgIMRT

Cited by 13 publications

References 22 publications

Medical physics challenges in clinical MR-guided radiotherapy

Medical physics challenges in clinical MR-guided radiotherapy

Head and neck radiotherapy on the MR linac: a multicenter planning challenge amongst MRIdian platform users

3D star shot analysis using MAGAT gel dosimeter for integrated imaging and radiation isocenter verification of MR‐Linac system

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