{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,10]],"date-time":"2026-03-10T00:29:23Z","timestamp":1773102563842,"version":"3.50.1"},"reference-count":38,"publisher":"Wiley","issue":"2","license":[{"start":{"date-parts":[[2026,2,16]],"date-time":"2026-02-16T00:00:00Z","timestamp":1771200000000},"content-version":"vor","delay-in-days":15,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"},{"start":{"date-parts":[[2026,2,1]],"date-time":"2026-02-01T00:00:00Z","timestamp":1769904000000},"content-version":"tdm","delay-in-days":0,"URL":"http:\/\/doi.wiley.com\/10.1002\/tdm_license_1.1"}],"content-domain":{"domain":["aapm.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Medical Physics"],"published-print":{"date-parts":[[2026,2]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>MR\u2010guided radiotherapy enables real\u2010time imaging and adaptive treatment but may introduce magnetic field effects that alter dose deposition. Accurate dose calculation in such settings requires detailed Monte Carlo (MC) modeling.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Purpose<\/jats:title>\n                    <jats:p>To develop and validate a detailed MC model of the 0.5 T bi\u2010planar Linac\u2010MR with an integrated, custom\u2010designed multileaf collimator (MLC) module in TOPAS.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>A MC Model of the 0.5\u00a0T bi\u2010planar Linac\u2010MR with a 6\u00a0MV FFF beam, commercialized as the Aurora\u2010RT (MagnetTx Oncology Solutions, Canada), is developed in TOPAS. A custom 3D magnetic field vector map, tracking with gantry angle, is incorporated into this TOPAS model. An electron source is used for X\u2010ray generation, and all components of the linac head from the target downward are modeled in detail. The MLCs are modeled from stereolithography (STL) design files and controlled via an empirically driven mechanism developed in this work. Water tank measured percent depth dose (PDD) curves and profiles (33\u00a0 to 2525\u00a0) are compared to MC simulated data to optimize the electron source energy and radial distribution. Additionally, output factors are simulated and compared to measurements. MLC transmission at 10\u00a0cm depth in solid water is simulated and measured using GAFChromic EBT3 film. MLC positioning accuracy is evaluated by comparing off\u2010axis MLC\u2010defined field profiles measured at 10\u00a0cm depth in water. The MC model's dose calculation accuracy is further evaluated by comparing measured and simulated surface doses using EBT3 film, and PDDs in slab phantoms using parallel plate chambers. Surface dose is measured by placing films at the surface and 5\u00a0cm depth in a solid water phantom. PDDs are measured and simulated in the following slab phantom configurations: polystyrene and polystyrene\u2013bone\u2013lung\u2013polystyrene.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      A 5.5\u00a0MeV electron source energy and a 1.3\u00a0mm radial distribution (FWHM) provides the best match between measurement and MC. Simulated PDDs pass 1%1\u00a0mm gamma criteria at 100% compared to measurements for all fields investigated. Simulated profiles at various depths for all fields (33\u00a0 to 2525\u00a0) score  96.7% in 2%2\u00a0mm compared to measurement. Evaluated output factors are in good agreement with measurement (within 1%) for all fields except 33\u00a0 (within 1.5%). The 2%2\u00a0mm gamma pass\u2010rates for MLC defined off\u2010axis fields are 98%. The maximum mean Distance\u2010To\u2010Agreement (DTA) in the penumbra region (1% criteria) and mean dose difference in central region for inline and crossline profiles, are 1\u00a0mm and 1%, respectively. MC simulated MLC transmission at central axis (0.28% \u2013 0.29%) is in good agreement with measurement (0.28% \u2013 0.44%). Film surface dose relative to D\n                      <jats:sub>max<\/jats:sub>\n                      is 74.4% in measurement and 73.6% in simulation. Lastly heterogeneous phantom PDDs passed 1%1\u00a0mm gamma criteria at % compared to measurement.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>The developed TOPAS MC model of the 0.5\u00a0T Linac\u2010MR demonstrates high accuracy for dose verification in magnetic fields. The MLC module, including its coordinate positioning mechanism, is fully validated for open aperture applications. This MC model provides a reliable framework for dose simulations in a magnetic\u00a0field.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1002\/mp.70329","type":"journal-article","created":{"date-parts":[[2026,2,17]],"date-time":"2026-02-17T06:57:37Z","timestamp":1771311457000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Development and validation of a TOPAS Monte Carlo model for a 0.5 T bi\u2010planar Linac\u2010MR"],"prefix":"10.1002","volume":"53","author":[{"given":"Alireza","family":"Gazor","sequence":"first","affiliation":[{"name":"Medical Physics Division, Department of Oncology University of Alberta Edmonton Alberta Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Michael","family":"Reynolds","sequence":"additional","affiliation":[{"name":"BC Cancer \u2010 Victoria, Medical Physics Victoria British Columbia Canada"},{"name":"University of Victoria, Department of Physics and Astronomy Victoria British Columbia Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Andrei","family":"Ghila","sequence":"additional","affiliation":[{"name":"Medical Physics Division, Department of Oncology University of Alberta Edmonton Alberta Canada"},{"name":"Department of Medical Physics Cross Cancer Institute Edmonton Alberta Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Eugene","family":"Yip","sequence":"additional","affiliation":[{"name":"Medical Physics Division, Department of Oncology University of Alberta Edmonton Alberta Canada"},{"name":"Department of Medical Physics Cross Cancer Institute Edmonton Alberta Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Keith","family":"Wachowicz","sequence":"additional","affiliation":[{"name":"Medical Physics Division, Department of Oncology University of Alberta Edmonton Alberta Canada"},{"name":"Department of Medical Physics Cross Cancer Institute Edmonton Alberta Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"B. Gino","family":"Fallone","sequence":"additional","affiliation":[{"name":"Medical Physics Division, Department of Oncology University of Alberta Edmonton Alberta Canada"},{"name":"Department of Medical Physics Cross Cancer Institute Edmonton Alberta Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tania R.","family":"Wood","sequence":"additional","affiliation":[{"name":"Medical Physics Division, Department of Oncology University of Alberta Edmonton Alberta Canada"},{"name":"Department of Medical Physics Cross Cancer Institute Edmonton Alberta Canada"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2026,2,16]]},"reference":[{"key":"e_1_2_8_2_1","doi-asserted-by":"publisher","DOI":"10.1007\/978-3-031-48165-9_11"},{"key":"e_1_2_8_3_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.semradonc.2023.10.009"},{"key":"e_1_2_8_4_1","doi-asserted-by":"publisher","DOI":"10.1088\/0031\u20109155\/53\/4\/006"},{"key":"e_1_2_8_5_1","doi-asserted-by":"publisher","DOI":"10.1002\/mp.17363"},{"key":"e_1_2_8_6_1","doi-asserted-by":"publisher","DOI":"10.1002\/mp.17246"},{"key":"e_1_2_8_7_1","unstructured":"F\u00e4lthC.Monte\u2010Carlo computations of dose distributions for magnetic resonance guided radiotherapy. 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