Multiparametric MRI of Rectal Cancer in the Assessment of Response to Therapy: A Systematic Review

BACKGROUND: Conventional MRI is limited in the assessment of nodal status and T status after neoadjuvant chemoradiotherapy. Multiparametric MRI strives to overcome these issues by directly measuring the local microcirculation and cellular environment, thus possibly allowing for a more reliable evaluation of response to therapy. OBJECTIVE: We assessed the available literature for the value of multiparametric MRI sequences (diffusion-weighted and dynamic contrast-enhanced imaging) in determining the response to neoadjuvant chemoradiotherapy in patients with rectal cancer. DATA SOURCES: We conducted a systematic literature research in the PubMed database. STUDY SELECTION: English-language publications of the years 2000-2013 that applied multiparametric MRI in the neoadjuvant setting were included in this study. INTERVENTION: Patients received neoadjuvant chemoradiotherapy and MRI examinations for staging and assessment of response. MAIN OUTCOME MEASURES: Accuracy, specificity, and sensitivity of MRI in prediction/assessment of response to therapy were the included measures. RESULTS: Forty-three studies were included in this review; 30 of them included diffusion-weighted imaging sequences, and 13 included dynamic contrast-enhanced MRI. Conventional MRI is limited in the accuracy of both T and N stages and response assessment. Diffusion-weighted imaging and dynamic contrast-enhanced MRIs showed additional value in both the prediction and detection of (complete) response to therapy compared with conventional sequences alone, as well as in correct N staging along with new experimental contrast agents. LIMITATIONS: The lack of standardization represents an important technical limitation. Most studies are conducted in an experimental setting; therefore, larger multicenter prospective studies are needed to verify the present findings. CONCLUSIONS: Advanced, functional MRI techniques allow for the quantification of tumor biological processes, such as microcirculation, vascular permeability, and tissue cellularity. This new technology has begun to show potential advantages over standard morphologic imaging in the restaging of rectal cancer, allowing for more accurate prognostication of response and potentially introducing an era allowing earlier treatment alteration and more accurate noninvasive surveillance, which could improve patient outcomes.