MRI assessment of rectal cancer response to neoadjuvant therapy: a multireader study.

OBJECTIVES: A watch and wait strategy with the goal of organ preservation is an emerging treatment paradigm for rectal cancer following neoadjuvant treatment. However, the selection of appropriate patients remains a challenge. Most previous efforts to measure the accuracy of MRI in assessing rectal cancer response used a small number of radiologists and did not report variability among them. METHODS: Twelve radiologists from 8 institutions assessed baseline and restaging MRI scans of 39 patients. The participating radiologists were asked to assess MRI features and to categorize the overall response as complete or incomplete. The reference standard was pathological complete response or a sustained clinical response for > 2 years. RESULTS: We measured the accuracy and described the interobserver variability of interpretation of rectal cancer response between radiologists at different medical centers. Overall accuracy was 64%, with a sensitivity of 65% for detecting complete response and specificity of 63% for detecting residual tumor. Interpretation of the overall response was more accurate than the interpretation of any individual feature. Variability of interpretation was dependent on the patient and imaging feature investigated. In general, variability and accuracy were inversely correlated. CONCLUSIONS: MRI-based evaluation of response at restaging is insufficiently accurate and has substantial variability of interpretation. Although some patients' response to neoadjuvant treatment on MRI may be easily recognizable, as seen by high accuracy and low variability, that is not the case for most patients. KEY POINTS: • The overall accuracy of MRI-based response assessment is low and radiologists differed in their interpretation of key imaging features. • Some patients' scans were interpreted with high accuracy and low variability, suggesting that these patients' pattern of response is easier to interpret. • The most accurate assessments were those of the overall response, which took into consideration both T2W and DWI sequences and the assessment of both the primary tumor and the lymph nodes.

Assessment of liver tumor response to therapy: role of quantitative imaging.

Quantitative imaging is the analysis of retrieved numeric data from images with the goal of reducing subjective assessment. It is an increasingly important radiologic tool to assess treatment response in oncology patients. Quantification of response to therapy depends on the tumor type and method of treatment. Anatomic imaging biomarkers that quantify liver tumor response to cytotoxic therapy are based on temporal change in the size of the tumors. Anatomic biomarkers have been incorporated into the World Health Organization criteria and the Response Evaluation Criteria in Solid Tumors (RECIST) versions 1.0 and 1.1. However, the development of novel therapies with different mechanisms of action, such as antiangiogenesis or radioembolization, has required new methods for measuring response to therapy. This need has led to development of tumor- or therapy-specific guidelines such as the Modified CT Response Evaluation (Choi) Criteria for gastrointestinal stromal tumors, the European Association for Study of the Liver (EASL) criteria, and modified RECIST for hepatocellular carcinoma, among many others. The authors review the current quantification criteria used in the evaluation of treatment response in liver tumors, summarizing their indications, advantages, and disadvantages, and discuss future directions with newer methods that have the potential for assessment of treatment response. Knowledge of these quantitative methods is important to facilitate pivotal communication between oncologists and radiologists about cancer treatment, with benefit ultimately accruing to the patient.