| Summary: | <p>Abstract</p> <p>Background</p> <p>To evaluate the accuracy of the combined maximum and minimum intensity projection-based internal target volume (ITV) delineation in 4-dimensional (4D) CT scans for liver malignancies.</p> <p>Methods</p> <p>4D CT with synchronized IV contrast data were acquired from 15 liver cancer patients (4 hepatocellular carcinomas; 11 hepatic metastases). We used five approaches to determine ITVs: (1). ITV<sub>AllPhases</sub>: contouring gross tumor volume (GTV) on each of 10 respiratory phases of 4D CT data set and combining these GTVs; (2). ITV<sub>2Phase</sub>: contouring GTV on CT of the peak inhale phase (0% phase) and the peak exhale phase (50%) and then combining the two; (3). ITV<sub>MIP</sub>: contouring GTV on MIP with modifications based on physician's visual verification of contours in each respiratory phase; (4). ITV<sub>MinIP</sub>: contouring GTV on MinIP with modification by physician; (5). ITV<sub>2M</sub>: combining ITV<sub>MIP </sub>and ITV<sub>MinIP</sub>. ITV<sub>AllPhases </sub>was taken as the reference ITV, and the metrics used for comparison were: matching index (MI), under- and over-estimated volume (V<sub>under </sub>and V<sub>over</sub>).</p> <p>Results</p> <p>4D CT images were successfully acquired from 15 patients and tumor margins were clearly discernable in all patients. There were 9 cases of low density and 6, mixed on CT images. After comparisons of metrics, the tool of ITV<sub>2M </sub>was the most appropriate to contour ITV for liver malignancies with the highest MI of 0.93 ± 0.04 and the lowest proportion of V<sub>under </sub>(0.07 ± 0.04). Moreover, tumor volume, target motion three-dimensionally and ratio of tumor vertical diameter over tumor motion magnitude in cranio-caudal direction did not significantly influence the values of MI and proportion of V<sub>under</sub>.</p> <p>Conclusion</p> <p>The tool of ITV<sub>2M </sub>is recommended as a reliable method for generating ITVs from 4D CT data sets in liver cancer.</p>
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