Interobserver Variability in Contouring Hepatocellular Carcinoma at a Tertiary Center

The optimal imaging test for delineation of the gross tumor volume (GTV) in hepatocellular carcinoma has not been defined. The hypothesis is that magnetic resonance imaging (MRI) allows for better visualization of the extent of tumor and will optimize the accuracy of tumor delineation for liver stereotactic radiotherapy compared with computed tomography (CT) only. We evaluated the interobserver agreement in GTV of hepatocellular carcinoma in a multicenter panel and compared MRI and CT in GTV delineation.

After the institutional review boards approved the study, we analyzed anonymous CT and MRI obtained from five patients with hepatocellular carcinoma. Eight radiation oncologists at our center used CT and MRI to delineate five GTVs of liver tumors. In both CT and MRI, the GTV volumes were compared.

The median GTV volume on MRI was 2.4 cm (range=0.59-15.6 cm) compared to 3.5 cm (range=0.52-24.9 cm) on CT (p=0.36). The GTV volume as defined on MRI was larger or at least as large as the GTV volume on CT in two cases. Variance and standard deviation between observers in CT and MRI were minor (6 vs. 7.87 cm, and 2.5 vs. 2.8 cm respectively).

In cases with well-defined tumors, CT is easier and reproducible. In cases with no defined tumor in CT, other tools are needed and MRI can be complementary. The interobserver variability in target delineation of hepatocellular carcinoma in this study is noteworthy.