Evaluation of a Simplified Intravoxel Incoherent Motion (IVIM) Analysis of Diffusion-Weighted Imaging for Prediction of Tumor Size Changes and Imaging Response in Breast Cancer Liver Metastases Undergoing Radioembolization A Retrospective Single Center Analysis

To investigate the value of a simplified intravoxel incoherent motion (IVIM) analysis for evaluation of therapy-induced tumor changes and response of breast cancer liver metastases (mBRC) undergoing radioembolization. In 21 females (mean age 54 years, range 43-72) with mBRC tumor size changes and response evaluation criteria in solid tumors (RECIST) response to 26 primary radioembolization procedures were analyzed. Standard 1.5-T liver magnetic resonance imaging including respiratory-gated diffusion-weighted imaging (DWI) with b0=0 s/mm(2), b1=50 s/mm(2), b2=800s/mm(2) before and 6 weeks after each treatment was performed. In addition to the apparent diffusion coefficient (ADC)(0,800), the estimated diffusion coefficient D and the perfusion fraction f were determined using a simplified IVIM approach. For each radioembolization, the 2 largest treated metastases (if available) were analyzed. Lesions were categorized according to size changes into group A (reduction of longest diameter [LD]) and group B (LD increase) after 3 months. Radioembolization procedures were further categorized into response (partial response and stable disease) and nonresponse (progressive disease) according to RECIST after 3 months. ADC and D are given in 10(-6) mm(2)/s. Forty-five metastases were analyzed. Thirty-two lesions were categorized as A; 13 as B. Before therapy, group A lesions showed significantly larger f-values than B (P=0.001), but ADC(0,800) and D did not differ. After therapy, in group A lesions the ADC(0,800)- and D-values increased and f decreased (P<0.0001); in contrast in group B lesions f increased (P=0.001). Groups could be differentiated by preinterventional f and by changes of D and f between pre and postinterventional imaging (area under the curve [AUC] of 0.903, 0.747 and 1.0, respectively). Preinterventional parameters did not differ between responders and nonresponders according to RECIST. ADC(0,800)- and D-values showed a larger increase in responders compared with nonresponders (P=0.013 and P=0.001, respectively). After therapy f-values decreased significantly in responders (P=0.001). Good to excellent prediction of long-term RECIST response was possible by therapy-induced changes in LD, D, and f (AUC 0.903, 0.879, and 0.867, respectively). A simplified IVIM model-based analysis of early post-treatment DWI can deliver additional information on tumor size changes and long-term RECIST response after radioembolization of mBRC. The estimated perfusion fraction f is better suited for response assessment than the conventional ADC(0,800) or D. This can be useful to guide further treatment strategy.