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

Abstract

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.

Whole‐body MRI‐DWI for assessment of residual disease after completion of therapy in lymphoma: A prospective multicenter study

“…The main challenge for posttreatment assessment lies in differentiating between viable lymphomatous lesions and fibrotic tissue. Several previous studies in different malignancies have reported ADC measurements to be useful in the differentiation between residual or recurrent tumor and posttreatment changes . All these studies show an increase in sensitivity and specificity when adding (quantitative) DWI to the routine MRI sequences with significantly lower ADCs in residual or recurrent malignant lesions compared with those in (immature) fibrosis and granulation tissue, in keeping with the results of the present study.…”

Apparent Diffusion Coefficient Maps Integrated in Whole-Body MRI Examination for the Evaluation of Tumor Response to Chemotherapy in Patients with Multiple Myeloma

“…These findings suggest that baseline DWI may not have a prognostic value and may not predict response to treatment. This was reported also in patients with rectal cancer: pretherapy ADC values of responders were not significantly different from those of nonresponders (29,30). In contrast, it has been reported that early changes in ADC values can indicate the difference in response to treatment, as tumors with greater ADC increase tend to demonstrate a better response (22).…”

Diffusion-weighted MR imaging of the rectum: Clinical applications

“…Ippolito et al [71], in a series of 30 patients with LARC who underwent CRT, showed a significantly higher mean value of SUV max in PET/CT before treatment than after treatment along with a significantly lower ADC value before treatment than after treatment. The best predictors cut-off values for response were SUV max of 4.4 and an ADC value of 1.289 × 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.…”