{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,19]],"date-time":"2026-10-19T10:34:02Z","timestamp":1792406042461,"version":"4.4.0"},"reference-count":26,"publisher":"Wiley","issue":"8","license":[{"start":{"date-parts":[[2025,7,25]],"date-time":"2025-07-25T00:00:00Z","timestamp":1753401600000},"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":["J Applied Clin Med Phys"],"published-print":{"date-parts":[[2025,8]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:sec><jats:title>Introduction<\/jats:title><jats:p>Using diagnostic CT for radiotherapy (RT) planning can bypass traditional CT simulation but introduces challenges in patient positioning and Hounsfield unit (HU) fidelity, affecting dose accuracy. Here a Varian Ethos adaptive\u2010driven CT direct\u2010to\u2010treatment (DtT) multi\u2010fraction stereotactic body radiation therapy (SBRT) workflow is presented.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>This study employed institutional diagnostic PET\u2010CT images to generate an initial reference Ethos treatment plan. HU and dosimetric accuracy were validated for PET\u2010CT, Ethos CBCT images (with and without Hypersight (HS), and the gold\u2010standard helical CT simulators). Following the SBRT reference plan creation on the low dose diagnostic PET\u2010CT, the first fraction was delivered with a newly generated adaptive plan calculated on the HS CBCT (Ethos) images. For multi\u2010fraction treatments, the first day CBCT images and adaptive plan become the reference for subsequent IGRT treatments. This study includes workflow validation and initial three patient experience.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>The DtT adaptive SBRT workflow was successfully implemented, with initial end\u2010to\u2010end testing demonstrating feasibility. In\u2010house solutions were introduced to facilitate the adaptive to IGRT plan conversion. The Ethos system, especially with HS, maintained HU fidelity and dose calculation accuracy comparable to helical CTs. On\u2010table adaptive sessions were within 37\u201351 min, aligning with single\u2010fraction palliative studies. Subsequent non\u2010adaptive IGRT fractions were efficiently completed within 7\u201327 min.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions<\/jats:title><jats:p>This study demonstrates the feasibility of DtT adaptive\u2010driven multifraction SBRT using diagnostic PET\u2010CT. This approach reduces the need for on\u2010site patient presence prior to treatment, expands planning lead times, and improves overall efficiency in radiotherapy for well selected patients.<\/jats:p><\/jats:sec>","DOI":"10.1002\/acm2.70147","type":"journal-article","created":{"date-parts":[[2025,7,26]],"date-time":"2025-07-26T03:44:21Z","timestamp":1753501461000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":5,"title":["Adaptive\u2010driven CT simulation\u2010free multi\u2010fraction SBRT radiotherapy: Initial clinical experience"],"prefix":"10.1002","volume":"26","author":[{"given":"V. N.","family":"Malkov","sequence":"first","affiliation":[{"name":"Department of Radiation Oncology Mayo Clinic  Rochester Minnesota USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"B. 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