A practical methodology to improve the dosimetric accuracy of MR-based radiotherapy simulation for brain tumors |
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| Affiliation: | 1. Department of Clinical Oncology, Queen Elizabeth Hospital, Hong Kong;2. Department of Radiology, Queen Elizabeth Hospital, Hong Kong;1. Trillium Health Partners, Peel Regional Cancer Centre, Mississauga, ON, Canada;2. University of Toronto, Department of Radiation Oncology, Toronto, ON, Canada;3. University of Ryerson, Department of Physics, Toronto, Canada;4. Sunnybrook Health Sciences Centre, Toronto, Canada;5. York University, Department of Physics and Astronomy, Toronto, ON, Canada;1. Department of Medical Physics, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku Tokyo 104-0045, Japan;2. Department of Radiological Sciences, Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10, Higashioku, Arakawa-ku Tokyo 116-8551, Japan;3. Division of Research and Development for Boron Neutron Capture Therapy, National Cancer Center Exploratory Oncology Research & Clinical Trial Center, Tsukiji 5-1-1, Chuo-ku, Tokyo 104-0045, Japan;4. Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku Tokyo 104-0045, Japan;1. Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia;2. School of Physics, University of Western Australia, Perth, Western Australia, Australia;3. Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia;4. Department of Physical Sciences, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia;6. Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Victoria, Australia;5. Joint Department of Physics, Institute of Cancer Research and Royal Marsden National Health Service Foundation Trust, Sutton, Surrey, United Kingdom;7. School of Medicine and Public Health, University of Newcastle, Newcastle, New South Wales, Australia;1. UCLouvain, Institut de Recherche Experimentale et Clinique (IREC), Center of Molecular Imaging, Radiotherapy and Oncology(MIRO), 1200 Brussels, Belgium;2. Radiation Oncology Department, Cliniques Universitaires Saint-Luc, 1200 Brussels, Belgium;3. KULeuven Department of Oncology, Laboratory of Experimental Radiotherapy, 3000 Leuven, Belgium;1. School of Information and Physical Sciences, University of Newcastle, Newcastle, New South Wales, Australia;2. Department of Radiation Oncology, Calvary Mater Hospital, Newcastle, New South Wales, Australia;3. Commonwealth Scientific and Industrial Research Organisation, Australian E-Health Research Centre, Herston, Queensland, Australia;4. School of Engineering, University of Newcastle, Newcastle, New South Wales, Australia;1. Servicio de Radiofísica y Protección Radiológica. Hospital Clínico Universitario Virgen de la Arrixaca, ctra. Madrid-Cartagena s/n, 30120 El Palmar (Murcia), Spain |
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| Abstract: | PurposeTo investigate the dosimetric accuracy of synthetic computed tomography (sCT) images generated by a clinically-ready voxel-based MRI simulation package, and to develop a simple and feasible method to improve the accuracy.Methods20 patients with brain tumor were selected to undergo CT and MRI simulation. sCT images were generated by a clinical MRI simulation package. The discrepancy between planning CT and sCT in CT number and body contour were evaluated. To resolve the discrepancies, an sCT specific CT-relative electron density (RED) calibration curve was used, and a layer of pseudo-skin was created on the sCT. The dosimetric impact of these discrepancies, and the improvement brought about by the modifications, were evaluated by a planning study. Volumetric modulated arc therapy (VMAT) treatment plans for each patient were created and optimized on the planning CT, which were then transferred to the original sCT and the modified-sCT for dose re-calculation. Dosimetric comparisons and gamma analysis between the calculated doses in different images were performed.ResultsThe average gamma passing rate with 1%/1 mm criteria was only 70.8% for the comparison of dose distribution between planning CT and original sCT. The mean dose difference between the planning CT and the original sCT were −1.2% for PTV D95 and −1.7% for PTV Dmax, while the mean dose difference was within 0.7 Gy for all relevant OARs. After applying the modifications on the sCT, the average gamma passing rate was increased to 92.2%. Mean dose difference in PTV D95 and Dmax were reduced to −0.1% and −0.3% respectively. The mean dose difference was within 0.2 Gy for all OAR structures and no statistically significant difference were found.ConclusionsThe modified-sCT demonstrated improved dosimetric agreement with the planning CT. These results indicated the overall dosimetric accuracy and practicality of this improved MR-based treatment planning method. |
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| Keywords: | Synthetic CT MR-only radiotherapy Brain cancer |
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