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- Adjeiwaah, Mary, 1980-, et al.
(författare)
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Dosimetric Impact of MRI Distortions : A Study on Head and Neck Cancers
- 2019
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Ingår i: International Journal of Radiation Oncology, Biology, Physics. - : Elsevier. - 0360-3016 .- 1879-355X. ; 103:4, s. 994-1003
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To evaluate the effect of magnetic resonance (MR) imaging (MRI) geometric distortions on head and neck radiation therapy treatment planning (RTP) for an MRI-only RTP. We also assessed the potential benefits of patient-specific shimming to reduce the magnitude of MR distortions for a 3-T scanner.Methods and Materials: Using an in-house Matlab algorithm, shimming within entire imaging volumes and user-defined regions of interest were simulated. We deformed 21 patient computed tomography (CT) images with MR distortion fields (gradient nonlinearity and patient-induced susceptibility effects) to create distorted CT (dCT) images using bandwidths of 122 and 488 Hz/mm at 3 T. Field parameters from volumetric modulated arc therapy plans initially optimized on dCT data sets were transferred to CT data to compute a new plan. Both plans were compared to determine the impact of distortions on dose distributions.Results: Shimming across entire patient volumes decreased the percentage of voxels with distortions of more than 2 mm from 15.4% to 2.0%. Using the user-defined region of interest (ROI) shimming strategy, (here the Planning target volume (PTV) was the chosen ROI volume) led to increased geometric for volumes outside the PTV, as such voxels within the spinal cord with geometric shifts above 2 mm increased from 11.5% to 32.3%. The worst phantom-measured residual system distortions after 3-dimensional gradient nonlinearity correction within a radial distance of 200 mm from the isocenter was 2.17 mm. For all patients, voxels with distortion shifts of more than 2 mm resulting from patient-induced susceptibility effects were 15.4% and 0.0% using bandwidths of 122 Hz/mm and 488 Hz/mm at 3 T. Dose differences between dCT and CT treatment plans in D-50 at the planning target volume were 0.4% +/- 0.6% and 0.3% +/- 0.5% at 122 and 488 Hz/mm, respectively.Conclusions: The overall effect of MRI geometric distortions on data used for RTP was minimal. Shimming over entire imaging volumes decreased distortions, but user-defined subvolume shimming introduced significant errors in nearby organs and should probably be avoided.
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| 2. |
- Karlsson, Mikael, et al.
(författare)
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Dedicated magnetic resonance imaging in the radiotherapy clinic
- 2009
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Ingår i: International journal of radiation oncology, biology, physics. - : Elsevier BV. - 1879-355X .- 0360-3016. ; 74:2, s. 644-651
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To introduce a novel technology arrangement in an integrated environment and outline the logistics model needed to incorporate dedicated magnetic resonance (MR) imaging in the radiotherapy workflow. An initial attempt was made to analyze the value and feasibility of MR-only imaging compared to computed tomography (CT) imaging, testing the assumption that MR is a better choice for target and healthy tissue delineation in radiotherapy. METHODS AND MATERIALS: A 1.5-T MR unit with a 70-cm-bore size was installed close to a linear accelerator, and a special trolley was developed for transporting patients who were fixated in advance between the MR unit and the accelerator. New MR-based workflow procedures were developed and evaluated. RESULTS: MR-only treatment planning has been facilitated, thus avoiding all registration errors between CT and MR scans, but several new aspects of MR imaging must be considered. Electron density information must be obtained by other methods. Generation of digitally reconstructed radiographs (DRR) for x-ray setup verification is not straight forward, and reliable corrections of geometrical distortions must be applied. The feasibility of MR imaging virtual simulation has been demonstrated, but a key challenge to overcome is correct determination of the skeleton, which is often needed for the traditional approach of beam modeling. The trolley solution allows for a highly precise setup for soft tissue tumors without the invasive handling of radiopaque markers. CONCLUSIONS: The new logistics model with an integrated MR unit is efficient and will allow for improved tumor definition and geometrical precision without a significant loss of dosimetric accuracy. The most significant development needed is improved bone imaging.
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| 5. |
- Persson, Emilia, et al.
(författare)
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MR-OPERA : A Multicenter/Multivendor Validation of Magnetic Resonance Imaging-Only Prostate Treatment Planning Using Synthetic Computed Tomography Images
- 2017
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Ingår i: International Journal of Radiation Oncology, Biology, Physics. - : ELSEVIER SCIENCE INC. - 0360-3016 .- 1879-355X. ; 99:3, s. 692-700
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To validate the dosimetric accuracy and clinical robustness of a commercially available software for magnetic resonance (MR) to synthetic computed tomography (sCT) conversion, in an MR imaginge-only workflow for 170 prostate cancer patients.Methods and Materials: The 4 participating centers had MriPlanner (Spectronic Medical), an atlas-based sCT generation software, installed as a cloud-based service. A T2-weighted MR sequence, covering the body contour, was added to the clinical protocol. The MR images were sent from the MR scanner workstation to theMriPlanner platform. The sCT was automatically returned to the treatment planning system. Four MR scanners and 2 magnetic field strengths were included in the study. For each patient, a CT-treatment plan was created and approved according to clinical practice. The sCT was rigidly registered to the CT, and the clinical treatment plan was recalculated on the sCT. The dose distributions from the CT plan and the sCT plan were compared according to a set of dose-volume histogram parameters and gamma evaluation. Treatment techniques included volumetric modulated arc therapy, intensity modulated radiation therapy, and conventional treatment using 2 treatment planning systems and different dose calculation algorithms.Results: The overall (multicenter/multivendor) mean dose differences between sCT and CT dose distributions were below 0.3% for all evaluated organs and targets. Gamma evaluation showed a mean pass rate of 99.12% (0.63%, 1 SD) in the complete body volume and 99.97% (0.13%, 1 SD) in the planning target volume using a 2%/ 2-mm global gamma criteria.Conclusions: Results of the study show that the sCT conversion method can be used clinically, with minimal differences between sCT and CT dose distributions for target and relevant organs at risk. The small differences seen are consistent between centers, indicating that an MR imagingeonly workflow using MriPlanner is robust for a variety of field strengths, vendors, and treatment techniques.
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| 6. |
- Karlsson, Mikael, et al.
(författare)
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MR-only procedures for improved overall precision in radiotherapy
- 2009
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Ingår i: International Journal of Radiation Oncology Biology Physics. - : Elsevier BV. - 0360-3016. ; , s. S656-S656
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Konferensbidrag (refereegranskat)abstract
- Purpose/Objective(s) To reduce the overall geometrical uncertainty in radiotherapy by introducing a novel technology arrangement based on a dedicated MR in an integrated workflow. A new logistics model needed to incorporate MR in this way was developed and clinically evaluated. Testing the assumption that MR is a better choice for target and healthy tissue delineation in radiotherapy, the suggested procedure was analyzed with respect to feasibility and precision of MR-only imaging compared to CT. The focus of the present study was on the geometrical uncertainty which is connected to the required margins between PTV and CTV. Materials/Methods A 1.5-T “open bore” MR unit with a 70-cm-bore size, Siemens Espree, was installed in close proximity to a treatment unit. A new MR-based workflow procedure was developed where all target drawing and treatment planning was performed on MR-data only. For non-fixed soft tissue targets, e.g. prostate, a special trolley was developed for transporting patients, who were immobilized, between the MR unit and the accelerator. The geometrical uncertainty using the transport solution was added to the uncertainty originating from the target definition process and compared with the total uncertainty in a more conventional CT based workflow. Results MR-only treatment planning has been facilitated, thus avoiding all registration errors between CT and MR data, but several new aspects of MR imaging must be considered. Reliable corrections of geometrical distortions must be applied and electron density information must be obtained by other methods. The feasibility of MR virtual simulation has previously been demonstrated. However, a key challenge is improve the visualization of skeletal structures, which is often needed for the traditional approach of set-up verification. The trolley solution allows for a highly precise setup of soft tissue targets without the invasive handling of fiducial markers. In the overall analyses of geometrical uncertainties it was shown that the combined uncertainty is reduced with the MR based workflow, mostly because of reduced systematic uncertainties when the CT-image registration is avoided. Conclusions The new logistics model is efficient and will allow for improved tumor definition and geometrical precision without a significant loss of dosimetric accuracy. Treatment planning directly on MR images is a way to reduce the geometrical uncertainty for e.g. prostate treatments. MR aided patient positioning does not require implanted fiducial markers and will be facilitated by rigid MR-MR registration. Less precise soft tissue CT-CT or CT-MR registrations will thus be avoided.
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