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

Abstract

Background and purposeThis 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. Materials and methodsThis 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. ResultsThe 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| < 0.4) with the external marker and diaphragm displacements in many cases (proportions of 50% and 46%, respectively). ConclusionWe found some cases showing substantial displacement in lung tumor positions during EE BH, especially in the AP direction. Because these tumor position displacements did not correlate with surrogate markers and were difficult to detect, we recommend pretreatment evaluation of the four-dimensional motions of tumors during BH using cine CT.