The application of apparent diffusion coefficients derived from intratumoral and peritumoral zones for assessing pathologic prognostic factors in rectal cancer

Objective To investigate the diagnostic performance of the apparent diffusion coefficient (ADC) derived from intratumoral and peritumoral zones for assessing pathologic prognostic factors in rectal cancer. Materials and methods One hundred forty-six patients with rectal cancer who underwent preoperative MRI were prospectively enrolled. Two radiologists independently placed free-hand regions of interest (ROIs) in the largest tumor cross section and three small ROIs on the peritumoral zone adjacent to the tumor contour. Maximum values of tumor ADC (ADC tmax ), minimum values of tumor ADC (ADC tmin ), mean values of tumor ADC (ADC tmean ), mean values of peritumor ADC (ADC pmean ), and ADC pmean /ADC tmean (ADC ratio) were obtained on ADC maps and correlated with prognostic factors using uni- and multivariate logistic regression, and receiver operating characteristic curve (ROC) analysis. Results Interobserver agreement was excellent for ADC tmax and ADC tmean (intraclass correlation coefficient [ICC], 0.915–0.958), and were good for ADC tmin , ADC pmean , and ADC ratio (ICC, 0.774–0.878). The ADC ratio was significantly higher in the poor differentiation, T3–4 stage, lymph node metastasis (LNM)–positive, extranodal extension (ENE)–positive, tumor deposit (TD)–positive, and lymphovascular invasion (LVI)–positive groups than that in the well–moderate differentiation, T1–2 stage, LNM-negative, ENE-negative, TD-negative, and LVI-negative groups ( p = 0.008, < 0.001, < 0.001, 0.001, < 0.001, and < 0.001, respectively). The area under the ROC curve (AUC) of the ADC ratio was the highest for assessing poor differentiation (0.700), T3–4 stage (0.707), LNM-positive (0.776), TD-positive (0.848), and LVI-positive (0.778). Both the ADC ratio (AUC = 0.677) and ADC pmean (AUC = 0.686) showed higher diagnostic performance for assessing ENE. Conclusion The ADC ratio could provide better predictive performance for assessing preoperative prognostic factors in resectable rectal cancer. Key Points • Both the peritumor/tumor ADC ratio and ADC pmean are correlated with important prognostic factors of resectable rectal cancer. • Both peritumor ADC and peritumor/tumor ADC ratio had higher diagnostic performance than tumor ADC for assessment of prognostic factors in resectable rectal cancer. • Peritumor/tumor ADC ratio showed the most capability for the assessment of prognostic factors in resectable rectal cancer.