Cholangiocarcinoma size on magnetic resonance imaging versus pathologic specimen: Implications for radiation treatment planning.

PURPOSE: The accuracy of abdominal magnetic resonance imaging (MRI) in measuring gross tumor volume in patients with resectable cholangiocarcinoma (CC) is unknown. CC is a highly difficult tumor to visualize and treatment with dose-escalated radiation therapy requires clear tumor delineation. We aim to investigate the concordance between imaging and pathologic size in patients with resected CC to determine the usefulness of MRI for image guided treatment modalities. METHODS AND MATERIALS: The records of 51 patients with resected CC who underwent preoperative MRI were evaluated. Each preoperative MRI was individually reviewed by a diagnostic radiologist (P.M.), who was blinded to pathologic measurements. A combination of dynamic multiphase contrast-enhanced T1- and T2-weighted images, original imaging reports, and pathologic reports were reviewed for greatest tumor dimensions. A general linear regression model was used to examine the outcome MRI minus pathology using MRI report, T1-weighted measurement, or T2-weighted measurement. A multivariable regression model was fit to assess the association of other factors with pathologic underestimation. RESULTS: The median age was 69 years. Eleven tumors were categorized distal/extrahepatic, 17 hilar, and 23 intrahepatic CC. The median tumor size on pathology report was 3.00 cm (range, 0.3-19). The median tumor size from the MRI report was 3 cm (range, 0.80-16.20) and median tumor size on independent radiological review was 3 cm (range, 0.90-17) on the T1-weighted and 3 cm (range, 0.90-17) on the T2-weighted MRI sequences. When compared with pathologic tumor size, the MRI report dimension was found to underestimate tumor size by 4.1 mm (P = .04). On multivariable analysis, pathologic size underestimation was influenced by increasing tumor size (slope, -0.20; P < .001); however, underestimation was not affected by tumor location or MRI sequence. CONCLUSIONS: MRI underestimates tumor size, which was more pronounced with larger tumors, but not influenced by tumor location. The potential for gross tumor volume underestimation should be considered when planning highly conformal radiation therapy treatment of CC.