Validation of Feasibility of Magnetic Resonance Imaging for the Measurement of Depth of Tumor Invasion in Distal Bile Duct Cancer According to the New American Joint Committee on Cancer Staging System

Rationale and Objectives This study aimed to develop and validate a method for measuring the depth of tumor invasion (DoI) using magnetic resonance imaging (MRI) and to investigate the diagnostic performance of the measured DoI for stratifying tumor (T) classification in patients with distal bile duct cancer according to the new American Joint Committee on Cancer staging system. Materials and Methods Fifty-four patients (30 men and 24 women; age range, 43–81 years) with distal bile duct cancer were enrolled. A study coordinator first developed a “provisional method” for measuring DoI on T2-weighted MRI. Subsequently, after compensating for defects, the “improved method” was developed. Two reviewers independently measured DoI and assessed its correlations with the histopathologic reference standard using intraclass correlation coefficient (ICC). The study population was grouped according to the DoI for T classification based on the new staging system for evaluation of diagnostic predictive values. Results The ICC values between the radiologic and the histopathologic DoI were calculated. Using the “improved method,” the ICC for the coordinator's DoI was very good (ICC, 0.885), which was a significantly higher value than that obtained using the “provisional method” (ICC, 0.501, P =.00000); and for two reviewers’ DoIs, the ICC values were good (ICC, 0.752 and 0.784, respectively). The overall accuracy of MRI for stratifying bile duct tumors using DoI was 87.0% and 85.2%, respectively. Conclusions This newly developed method reliably measured DoI on T2-weighted MRI and can be used for preoperative T classification of patients with distal bile duct cancer according to the new staging system.