{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,19]],"date-time":"2026-09-19T07:26:30Z","timestamp":1789802790672,"version":"4.0.1"},"reference-count":26,"publisher":"Wiley","issue":"4","license":[{"start":{"date-parts":[[2015,3,17]],"date-time":"2015-03-17T00:00:00Z","timestamp":1426550400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"},{"start":{"date-parts":[[2015,9,1]],"date-time":"2015-09-01T00:00:00Z","timestamp":1441065600000},"content-version":"tdm","delay-in-days":168,"URL":"http:\/\/doi.wiley.com\/10.1002\/tdm_license_1.1"}],"content-domain":{"domain":["aip.org"],"crossmark-restriction":true},"short-container-title":["Medical Physics"],"published-print":{"date-parts":[[2015,4]]},"abstract":"<jats:sec><jats:title>Purpose:<\/jats:title><jats:p>(1) To validate retrospective markerless tracking software for small lung tumors by comparing tracked motion in 4\u2010dimensional planning computed tomography (4DCT) derived kV projection images and known tumor motion in the same 4DCT. (2) To evaluate variability of tumor motion using kV projection images from cone\u2010beam computed tomography (CBCT) scans acquired on different days.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods:<\/jats:title><jats:p>Nonclinical tumor tracking software (TTS) used a normalized cross correlation algorithm to track the tumor on enhanced kV projection images (e.g., from a CBCT scan). The reference dataset consisted of digitally reconstructed radiographs (DRRs) from one phase of a planning 4DCT. TTS matches two in\u2010plane coordinates and obtains the out\u2010of\u2010plane coordinate by triangulating with match results from other projections. (1) To validate TTS, tracking results were compared with known 4DCT tumor motion for two patients (A and B). Projection images (1 image\/1\u00b0) were digitally reconstructed for each 4DCT phase. From these, kV projection series were composed simulating full breathing cycles every 20\u00b0 of gantry rotation [breathing period = 20\u00b0\/(6\u00b0\/s) = 3.33 s]. Reference templates were 360 \u201ctumor enhanced\u201d DRRs from the 4DCT expiration phase. TTS\u2010derived tumor motion was compared to known tumor motion on 4DCT. (2) For five patients, TTS\u2010assessed motion during clinical CBCT acquisition was compared with motion on the planning 4DCT, and the motion component in the <jats:italic>Y<\/jats:italic> (cranio\u2013caudal)\u2010direction was compared with the motion of an external marker box (RPM, real\u2010time position management).<\/jats:p><\/jats:sec><jats:sec><jats:title>Results:<\/jats:title><jats:p>(1) Validation results: TTS for case A (tumor 6.2 cm<jats:sup>3<\/jats:sup>, 32 mm axial diameter) over 360\u00b0 showed mean motion <jats:italic>X<\/jats:italic> (medial\u2013lateral) = 3.4, <jats:italic>Y<\/jats:italic> = 11.5, and <jats:italic>Z<\/jats:italic> (ventral\u2013dorsal) = 4.9 mm (1 SD &lt; 1.0 mm). Corresponding 4DCT motion was <jats:italic>X<\/jats:italic> = 3.1, <jats:italic>Y<\/jats:italic> = 11.3, and <jats:italic>Z<\/jats:italic> = 5.1 mm. Correlation coefficients between TTS tumor motion and displacement of the tumor's center of mass (CoM) on 4DCT were 0.64, 0.96, and 0.82 (<jats:italic>X<\/jats:italic>, <jats:italic>Y<\/jats:italic>, and <jats:italic>Z<\/jats:italic>, respectively). For case B (4.1 cm<jats:sup>3<\/jats:sup>, 20 mm diameter), due to temporarily decreased tumor visibility preventing TTS from resolving the tumor, robust tracking data were only available between angles 300\u00b0\u201340\u00b0 and 120\u00b0\u2013220\u00b0. Mean motion according to TTS was <jats:italic>X<\/jats:italic> = 2.0, <jats:italic>Y<\/jats:italic> = 7.7, and <jats:italic>Z<\/jats:italic> = 8.2 mm (1 SD &lt; 0.9 mm). Tumor motion on 4DCT was <jats:italic>X<\/jats:italic> = 1.8, <jats:italic>Y<\/jats:italic> = 7.6, and <jats:italic>Z<\/jats:italic> = 9.5 mm and correlation coefficients between TTS motion and CoM displacement were 0.59, 0.95, and 0.93 (<jats:italic>X<\/jats:italic>, <jats:italic>Y<\/jats:italic>, and <jats:italic>Z<\/jats:italic>, respectively). (2) Clinical results: TTS revealed a mean intrafraction variation in tumor motion in <jats:italic>Y<\/jats:italic>\u2010direction of &gt;2.0 mm (1 SD) in four of five patients. In addition, clinical tumor motion amplitude differed from that seen on planning 4DCT. Internal and external structures that create abrupt density change (e.g., table\u2010top edge, interface between lung\/mediastinum and lung\/heart) were observed to prevent 360\u00b0 tracking of the tumor. Correlation coefficients between TTS motion in the <jats:italic>Y<\/jats:italic>\u2010direction and the RPM signal (22 observations) ranged from 0.78 to 0.96. In 2D, 241 TTS matches at end\u2010inspiration and end\u2010expiration were visually validated: mean difference was 0.8 mm (SD = 0.7) for both.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions:<\/jats:title><jats:p>TTS can track small lung tumors if these are visible in kV projections. A 4DCT dataset can be used to validate kV tracking of moving targets. TTS and 4DCT displacement agreed to within 2 mm. TTS and RPM motion were closely associated but tumor motion during CBCT can vary from the planning 4DCT.<\/jats:p><\/jats:sec>","DOI":"10.1118\/1.4914401","type":"journal-article","created":{"date-parts":[[2015,3,17]],"date-time":"2015-03-17T18:27:31Z","timestamp":1426616851000},"page":"1640-1652","update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":41,"title":["Markerless tracking of small lung tumors for stereotactic radiotherapy"],"prefix":"10.1002","volume":"42","author":[{"given":"John R.","family":"van S\u00f6rnsen de Koste","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Max","family":"Dahele","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hassan","family":"Mostafavi","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alex","family":"Sloutsky","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Suresh","family":"Senan","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ben J.","family":"Slotman","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wilko F. 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