Evaluation of the four-dimensional motion of lung tumors during end-exhalation breath-hold conditions using volumetric cine computed tomography images

•Evaluation of lung tumor 4D motion during breath-holding (BH) using cine CT.•Some cases showed substantial tumor motion in the posterior directions during BH.•Surrogate markers (external marker/diaphragm) did not detect tumor motion.•In 18% of cases, tumor motion during BH was larger than that during free breathing.•Pretreatment evaluation of the tumor motion during BH using cine CT is recommended. This study was performed to evaluate the four-dimensional motion of lung tumors during end-exhalation (EE) breath-holding (BH) using cine computed tomography (CT) and investigate the correlation between tumor and surrogate marker motions. This study included 28 patients who underwent stereotactic body radiation therapy at our institution and were capable of 15–20 s of EE BH within a ±1.5-mm gating window with external markers. During EE BH with cine CT, 21 s of continuous data were acquired using 320-row multislice CT. Displacements in the tumor position during EE BH were assessed in the left–right (LR), anterior–posterior (AP), and superior–inferior (SI) directions. Pearson’s correlation coefficient (r) between tumor motions during EE BH and diaphragm/external marker motions was also determined. The mean absolute maximum displacements of the tumor position during EE BH were 1.3 (range: 0.2–4.0), 1.9 (range: 0.3–12.0), and 1.3 (range: 0.1–7.2) mm in the LR, AP, and SI directions, respectively. The displacement of the tumor position in the AP direction was weakly correlated (|r|