Hung‐Jen ChenJi‐An LiangChih‐Yi ChenYang‐Hao YuChun‐Ru Chien2026-01-292026-01-292016-11-1810.1111/1759-7714.12405https://scholars.csmu.edu.tw/handle/123456789/3505<jats:p>Stereotactic body radiation therapy (<jats:styled-content style="fixed-case">SBRT</jats:styled-content>) plays an important role in early stage non‐small cell lung cancer. Tumor growth before radiotherapy planning (<jats:styled-content style="fixed-case">RTP</jats:styled-content>) or during <jats:styled-content style="fixed-case">SBRT</jats:styled-content> has been reported in lung cancer patients; however, little is known of growth during the period in‐between (i.e. after <jats:styled-content style="fixed-case">RTP</jats:styled-content> but before <jats:styled-content style="fixed-case">SBRT</jats:styled-content>). An 83‐year‐old man referred to our hospital and diagnosed with medically inoperable non‐small cell lung cancer was noted to have significant tumor progression on <jats:styled-content style="fixed-case">d</jats:styled-content>ay 1 of cone beam computed tomography just before the planned <jats:styled-content style="fixed-case">SBRT</jats:styled-content> delivery. Because of uncertainty of the underlying etiology and unfamiliarity with this phenomenon, we made a clinical decision to arrange re‐simulation and revise our treatment to conventional fractionated radiotherapy (<jats:styled-content style="fixed-case">CFRT</jats:styled-content>). After an initial response, distant metastases occurred eight months after <jats:styled-content style="fixed-case">CFRT.</jats:styled-content> The patient received best supportive care and was under hospice care at the last follow‐up (27 months after <jats:styled-content style="fixed-case">CFRT</jats:styled-content>). We report a case with significant tumor growth just before planned <jats:styled-content style="fixed-case">SBRT</jats:styled-content>. Optimal management in this scenario requires further investigation.</jats:p>[SDGs]SDG3journal-article