Locally advanced rectal cancer: post-chemoradiotherapy ADC histogram analysis for predicting a complete response

Abstract

Background

The value of diffusion-weighted imaging (DWI) for reliable differentiation between pathologic complete response (pCR) and residual tumor is still unclear. Recently, a few studies reported that histogram analysis can be helpful to monitor the therapeutic response in various cancer research.

Purpose

To investigate whether post-chemoradiotherapy (CRT) apparent diffusion coefficient (ADC) histogram analysis can be helpful to predict a pCR in locally advanced rectal cancer (LARC).

Material and Methods

Fifty patients who underwent preoperative CRT followed by surgery were enrolled in this retrospective study, non-pCR (n = 41) and pCR (n = 9), respectively. ADC histogram analysis encompassing the whole tumor was performed on two post-CRT ADC₆₀₀ and ADC₁₀₀₀ (b factors 0, 600 vs. 0, 1000 s/mm²) maps. Mean, minimum, maximum, SD, mode, 10th, 25th, 50th, 75th, 90th percentile ADCs, skewness, and kurtosis were derived. Diagnostic performance for predicting pCR was evaluated and compared.

Results

On both maps, 10th and 25th ADCs showed better diagnostic performance than that using mean ADC. Tenth percentile ADCs revealed the best diagnostic performance on both ADC₆₀₀ (A_Z 0.841, sensitivity 100%, specificity 70.7%) and ADC₁₀₀₀ (A_Z 0.821, sensitivity 77.8%, specificity 87.8%) maps. In comparison between 10th percentile and mean ADC, the specificity was significantly improved on both ADC₆₀₀ (70.7% vs. 53.7%; P = 0.031) and ADC₁₀₀₀ (87.8% vs. 73.2%; P = 0.039) maps.

Conclusion

Post-CRT ADC histogram analysis is helpful for predicting pCR in LARC, especially, in improving the specificity, compared with mean ADC.