Locally advanced rectal cancer: value of ADC mapping in prediction of tumor response to radiochemotherapy.

PURPOSE: To evaluate the diagnostic performance of quantitative apparent diffusion coefficient (ADC) measurements, in the assessment of the therapeutic response to chemo-radiation therapy (CRT) in patients with locally advanced rectal cancer, by analyzing post CRT values of ADC, in relation to tumor regression grade (TRG) obtained by histopathologic evaluation of the rectal specimen. METHODS: This prospective study was approved by an Institutional Review Board, and informed consent was obtained from all patients. Thirty-one patients with locally advanced rectal cancer underwent pre and post CRT MR imaging at 1.5T. ADC values were measured in regions of interest (ROIs) drawn independently by two radiologists, blinded to the pathology results, on three slices of the pre and post CRT DW-MR image sets with the corresponding T2 weighted images (T2WI) available for anatomic reference. The two readers' measurements were compared for differences in ADC values, inter-observer variability (measured as the intraclass correlation coefficient; ICC) and the ADC distributions of responders vs non-responders. The diagnostic performance of ADC in the prediction of the response to CRT was evaluated by calculating the area under the ROC curve (AUC) and the optimal cut-off values. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were assessed. RESULTS: The two readers showed an overall strong agreement in measuring ADC values. For both readers, no differences in ADC pre-treatment measurements were observed between responders and non-responders. For reader 1, the post-CRT ADC and the ΔADC presented the higher AUC (0.823 and 0.803, respectively), while Δ%ADC provided the lower AUC value (0.682). The optimal cutoff point was 1.294 s/mm(2) for post-CRT measures (sensitivity=86.4%, specificity=66.7%, PPV=86.4%, NPV=66.7%), 0.500 for ΔADC (sensitivity=81.8%, specificity=66.7%, PPV=85.7%, NPV=60.0%) and 59.3% for Δ%ADC (sensitivity=63.4%, specificity=66.7, PPV=82.4%, NPV=42.9%). Similar results were observed for reader 2, with better performance obtained with the ADC post-CRT (AUC of 0.833) and an optimal cut off of 1.277 × 10(-3)s/mm(2). CONCLUSION: Post-CRT ADC measurements are reliable and reproducible and may be used as a non-invasive tool to evaluate response to therapy as post-CRT ADC values and ΔADC presented good diagnostic performance to select responder patients.

Response to neoadjuvant therapy in locally advanced rectal cancer: assessment with diffusion-weighted MR imaging and 18FDG PET/CT.

The aim of this study was to evaluate the correlation between the changes of SUV(max) and of apparent diffusion coefficient (ADC) before and after neoadjuvant therapy, to enable us predict the therapy response, in patients with locally advanced rectal cancer (LARC). A total of 30 patients with LARC who underwent CRT were recruited for our study. All the patients underwent a whole body 18F-FDG-PET/CT scan and a pelvic MR examination including DW imaging for staging (PET/CT1 and RM1), and after the chemoradiation therapy (PET/CT2, and RM2). Histopathologic analysis of rectal specimen, according to tumor regression grade (Mandard's criteria) was used as the standard reference. MR and PET-CT images were analyzed, and measurements of ADC values and SUV(max) were taken. Diagnostic performance for selection of complete responders (TRG1-2) and overall diagnostic accuracy for each item were calculated. After neoadjuvant therapy, all patients were submitted to surgery. According to Mandard's criteria, 21 tumors showed complete (TRG1) or subtotal regression (TRG2) and were classified as responders; nine tumors were classified as non responders (TRG3, 4, and 5). In all the patients, mean value of SUV(max) in PET/CT1 was higher than those in PET/CT2 (P < 0.001), whereas mean ADC value was lower in RM1 than RM2 (P < 0.001), with a significant percentage decrease of values after the treatment (P < 0.005).The best predictors cut-off values for TRG response were SUV(max) of 4.4 and ADC of 1.28 × 10(3) mm(2)/s with sensitivity, specificity accuracy, negative predictive value, and positive predictive values of 77.3%, 88.9%, 80.7%, 61.5%, and 94.4%, respectively. We conclude from the overall data of this study that the absolute values of SUV(max) and ADC of rectal lesion after CRT were the best parameters to define the response to treatment, by differentiating fibrosis from viable tumor tissue.