Treatment response monitoring in patients with gastrointestinal stromal tumor using diffusion-weighted imaging: Preliminary results in comparison with positron emission tomography/computed tomography

We compared the parameters derived from diffusion-weighted imaging (DWI) and positron emission tomography/computed tomography (PET/CT) for treatment response evaluation and response prediction in patients with gastrointestinal stromal tumor (GIST). Seven patients with histologically proven metastatic disease were enrolled. DWI and PET/CT data were collected from all patients at diagnosis and from six at follow-up. All 37 lesions were identifiable in DWI with a sensitivity of 100%. To achieve higher accuracy, we used the apparent diffusion coefficient (ADC) of liver and background noise as thresholds for the measurement of the ADCs of lesions. Significant inverse correlations were found between ADC_{mean_thr} (ADC_mean with thresholds) and SUV_mean (mean standardized uptake value) (R²=0.523, p<0.001 at diagnosis, and R²=0.916, p<0.001 at follow-up), between ADC_{mean_thr} and SUV_max (maximum SUV) (R²=0.529, p<0.001 at diagnosis, and R²=0.761, p<0.001 at follow-up), between ΔADC_{mean_thr} (percentage change in ADC_{mean_thr}) and ΔSUV_mean (percentage change in SUV_mean) (R²=0.384, p<0.001), and between ΔADC_{mean_thr} and ΔSUV_max (percentage change in SUV_max) (R²=0.500, p<0.001). In lesion-based analysis, pre-treatment ADC_{mean_thr} outperformed SUV_mean and SUV_max in treatment response prediction, with an area under the receiver operating characteristic curve of 0.706. These results show that DWI can provide a quantitative assessment comparable with PET/CT in GIST lesion characterization, treatment response evaluation and response prediction.