Fractional order calculus model-derived histogram metrics for assessing pathological complete response to neoadjuvant chemotherapy in locally advanced rectal cancer

Aim: This study evaluates the value of diffusion fractional order calculus (FROC) model for the assessment of pathological complete response (pCR) after neoadjuvant chemoradiotherapy (nCRT) for locally advanced rectal cancer (LARC) by using histogram analysis derived from whole-tumor volumes. Materials and methods: Ninety-eight patients were prospectively included. Every patient received MRI scans before and after nCRT using a 3.0-Tesla MRI machine. Parameters of the FROC model, including the anomalous diffusion coefficient (D), intravoxel diffusion heterogeneity (beta), spatial parameter (mu), and the standard apparent diffusion coefficient (ADC), were calculated. Changes in median values (Delta X-median) and ratio (r Delta X-median) were calculated. Receiver operating characteristic (ROC) curves were used for evaluating the diagnostic performance. Results: Pre-treatment beta-10th percentile values were significantly lower in the pCR group compared to the non-pCR group (p < 0.001). The Delta beta-median showed higher diagnostic accuracy (AUC = 0.870) and sensitivity (76.67 %) for predicting tumor response compared to MRI tumor regression grading (mrTRG) scores (AUC = 0.722; sensitivity = 90.0 %). Discussion: The use of FROC alongside comprehensive tumor histogram analysis was found to be practical and effective in evaluating the tumor response to nCRT in LARC patients.