{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,21]],"date-time":"2026-01-21T05:37:57Z","timestamp":1768973877844,"version":"3.49.0"},"reference-count":40,"publisher":"Wiley","issue":"6","license":[{"start":{"date-parts":[[2025,4,3]],"date-time":"2025-04-03T00:00:00Z","timestamp":1743638400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["aapm.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Medical Physics"],"published-print":{"date-parts":[[2025,6]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>The clinical realization of markerless dynamic tumor tracking (MLDTT) has prompted a new paradigm shift to intrafraction imaging\u2010based quality assurance (QA). During MLDTT treatment using a gimbaled accelerator, the megavoltage (MV) imager serves as an independent system to leverage real\u2010time intrafraction monitoring. Soft\u2010tissue feature tracking has shown promise for tumor localization in confined MV projections, but studies demonstrating its application in clinical MLDTT treatments are scarse.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Purpose<\/jats:title>\n                    <jats:p>To validate MV image\u2010based dense soft\u2010tissue feature tracking for intrafraction position monitoring of lung tumors during MLDTT stereotactic body radiotherapy (SBRT), and report on the resolved geometric uncertainty.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>\n                      Ten non\u2010small cell lung cancer (NSCLC) patients underwent MLDTT\u2010SBRT using a commercial gimbal\u2010based system. During treatment, beam's\u2010eye\u2010view (BEV) projection images were captured at \u223c3 frames s\n                      <jats:sup>\u22121<\/jats:sup>\n                      (fps) using the electronic portal imaging device (EPID). MV sequences were streamed to a research workstation and processed off\u2010line using a purpose\u2010built algorithm, the soft\u2010tissue feature tracker (SoFT). Both the tumor and dynamic field aperture position were automatically extracted in the pan and tilt directions of the gimbaled x\u2010ray head, corresponding to the in\u2010plane lateral and longitudinal direction of the imager, and compared to ground truth manual tracking. The success, percentage of fields producing an output, and performance of MV tracking under the presence\/absence of anatomy\u2010related obstruction and multi\u2010leaf collimator (MLC) occlusion were quantified, including three\u2010dimensional conformal (3DCRT) and step\u2010and\u2010shoot intensity modulated radiotherapy (IMRT) deliveries. In addition, the geometric uncertainty of MLDTT treatment was estimated as the difference between field aperture and target center position in the BEV. The standard deviation of systematic (\n                      <jats:italic>\u03a3<\/jats:italic>\n                      ) and random (\n                      <jats:italic>\u03c3<\/jats:italic>\n                      ) errors were determined.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      MV tracking was successful for 89.7% of (unmodulated) 3DCRT fields, as well as 82.4% of (modulated) control points (CPs) and subfields (SFs) for IMRT and field\u2010in\u2010field 3DCRT deliveries. The MV tracking accuracy was dependent on the traversed anatomy, tumor visibility, and occlusion by the MLC. The mean MV tracking accuracy was 1.2\u00a0mm (pan) and 1.4\u00a0mm (tilt), and a resultant 2D accuracy of 1.8\u00a0mm. The MV tracking performance within 2\u00a0mm was observed in 92.1% (pan) and 86.6% (tilt), respectively. The mean aperture\u2010target positional uncertainty smaller than 3\u00a0mm\/5\u00a0mm was observed in 94.4\/97.9% (pan) and 89.6\/96.7% (tilt) of the time. The group\n                      <jats:italic>\u03a3<\/jats:italic>\n                      and\n                      <jats:italic>\u03c3<\/jats:italic>\n                      were 0.5\u00a0mm\/0.8\u00a0mm (pan), and 0.7\u00a0mm\/1.2\u00a0mm (tilt), compared to 0.3\u00a0mm\/0.5\u00a0mm (pan), and 0.6\u00a0mm\/0.9\u00a0mm (tilt) based on the manual ground truth.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>MV imaging coupled with the soft\u2010tissue feature tracker algorithm constitutes a valuable non\u2010invasive method for independent intrafraction surveillance. Tracking multiple features has shown the potential to improve position estimation, notwithstanding obstruction, and occlusion challenges, facilitating the quantification of the geometric uncertainty of MLDTT treatment.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1002\/mp.17740","type":"journal-article","created":{"date-parts":[[2025,4,4]],"date-time":"2025-04-04T19:05:34Z","timestamp":1743793534000},"page":"4657-4674","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Megavoltage intrafraction monitoring and position uncertainty in gimbaled markerless dynamic tumor tracking treatment of lung tumors"],"prefix":"10.1002","volume":"52","author":[{"given":"Marco","family":"Serpa","sequence":"first","affiliation":[{"name":"Department of Radiation Oncology Universit\u00e4tsklinikum Erlangen, Friedrich\u2010Alexander\u2010Universit\u00e4t Erlangen\u2010N\u00fcrnberg  Erlangen Germany"},{"name":"Department of Radiation Oncology, Medical Center \u2010 University of Freiburg, Faculty of Medicine University of Freiburg, German Cancer Consortium (DKTK) partner site DKTK\u2010Freiburg  Freiburg Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tobias","family":"Brandt","sequence":"additional","affiliation":[{"name":"Department of Radiation Oncology Universit\u00e4tsklinikum Erlangen, Friedrich\u2010Alexander\u2010Universit\u00e4t Erlangen\u2010N\u00fcrnberg  Erlangen Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Simon K. 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