Value of Diffusion-Weighted Magnetic Resonance Imaging for Prediction and Early Assessment of Response to Neoadjuvant Radiochemotherapy in Rectal Cancer: Preliminary Results

Purpose To evaluate diffusion-weighted magnetic resonance imaging (DWI) for response prediction before and response assessment during and early after preoperative radiochemotherapy (RCT) for locally advanced rectal cancer (LARC). Methods and Materials Twenty patients receiving RCT for LARC underwent MRI including DWI before RCT, after 10–15 fractions and 1 to 2 weeks before surgery. Tumor volume and apparent diffusion coefficient (ADC; b-values: 0–1000 s/mm2 ) were determined at all time points. Pretreatment tumor ADC and volume, tumor ADC change (∆ADC), and volume change (∆V) between pretreatment and follow-up examinations were compared with histopathologic findings after total mesorectal excision (pathologic complete response [pCR] vs. no pCR, ypT0–2 vs. ypT3–4, T-downstaging or not). The discriminatory capability of pretreatment tumor ADC and volume, ∆ADC, and ∆V for the detection of pCR was compared with receiver operating characteristics analysis. Results Pretreatment ADC was significantly lower in patients with pCR compared with patients without (in mm2 /s: 0.94 ± 0.12 × 10−3 vs. 1.19 ± 0.22 × 10−3 , p = 0.003), yielding a sensitivity of 100% and specificity of 86% for detection of pCR. The volume reduction during and after RCT was significantly higher in patients with pCR compared with patients without (in %: ΔVduring : −62 ± 16 vs. −33 ± 16, respectively, p = 0.015; and ΔVpost : −86 ± 12 vs. −60 ± 21, p = 0.012), yielding a sensitivity of 83% and specificity of 71% for the ΔVduring and, respectively, 83% and 86% for the ΔVpost . The ∆ADC during (ΔADCduring ) and after RCT (ΔADCpost ) showed a significantly higher value in patients with pCR compared with patients without (in %: ΔADCduring : 72 ± 14 vs. 16 ± 12, p = 0.0006; and ΔADCpost : 88 ± 35 vs. 26 ± 19, p = 0.0011), yielding a sensitivity and specificity of 100% for the ΔADCduring and, respectively, 100% and 93% for the ΔADCpost. Conclusions These initial findings indicate that DWI, using pretreatment ADC, ΔADCduring , and ΔADCpost may be useful for prediction and early assessment of pathologic response to preoperative RCT of LARC, with higher accuracy than volumetric measurements.