Abstract
BackgroundTo 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.Methods4D 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). ITVAllPhases: contouring gross tumor volume (GTV) on each of 10 respiratory phases of 4D CT data set and combining these GTVs; (2). ITV2Phase: contouring GTV on CT of the peak inhale phase (0% phase) and the peak exhale phase (50%) and then combining the two; (3). ITVMIP: contouring GTV on MIP with modifications based on physician's visual verification of contours in each respiratory phase; (4). ITVMinIP: contouring GTV on MinIP with modification by physician; (5). ITV2M: combining ITVMIP and ITVMinIP. ITVAllPhases was taken as the reference ITV, and the metrics used for comparison were: matching index (MI), under- and over-estimated volume (Vunder and Vover).Results4D 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 ITV2M was the most appropriate to contour ITV for liver malignancies with the highest MI of 0.93 ± 0.04 and the lowest proportion of Vunder (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 Vunder.ConclusionThe tool of ITV2M is recommended as a reliable method for generating ITVs from 4D CT data sets in liver cancer.
Highlights
Primary and metastatic hepatic malignancies are commonly treated by surgery, but radiation therapy is one of options as non-surgical modalities
maximum intensity projection (MIP)-based internal target volume (ITV) delineation is performed on a single 3-D CT data set, where each pixel in this set represents the brightest object encountered by corresponding voxels in all volumetric 4D CT data sets, for instance, MIP-based ITV delineation for lung cancer, which was recommended as a reliable tool and a good first estimation [10,11,12]
Of these patients 11 had metastatic liver cancers and 4, hepatocellular carcinoma (HCC) with mean lesion volume of 152 cm3. 4D CT images were successfully obtained from 15 patients and tumor margins were clearly discernable in all patients
Summary
Primary and metastatic hepatic malignancies are commonly treated by surgery, but radiation therapy is one of options as non-surgical modalities. Manually contouring GTV in all 10 breath phases of a 4D scan image sets to form ITV, which is the most accurate tool to determine ITV, but it is a time-consuming and labor-intensive task. To reduce the workload of contouring multiple GTVs, one solution is to contour only two extreme phases at end-inhalation and endexhalation and to sum of the two becoming ITV [8,9]; and the other is to use the post-processing tools of maximum intensity projection (MIP) and minimum intensity projection (MinIP) from 4D CT data sets to generate ITV. MinIP-based ITV is on the CT set, where each pixel represents the lowest data value in the volumetric data [10]. 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
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