Diffusion-Weighted MRI as Predictor of Tumor Treatment Response

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AJR 2012; 199:W415 0361–803X/12/1993–W415 © American Roentgen Ray Society Diffusion-Weighted MRI as Predictor of Tumor Treatment Response We congratulate Ohno and colleagues [1] for their article, “Diffusion-Weighted MRI Versus 18F-FDG PET/CT: Performance as Predictors of Tumor Treatment Response and Patient Survival in Patients With Non–Small Cell Lung Cancer Receiving Chemoradiotherapy,” published in the January 2012 issue of the AJR. We believe that this article is informative and write to express our opinions with respect to diffusion-weighted MRI (DWI). The authors indicate that the average apparent diffusion coefficient (ADC) value shows the lesion more clearly than the minimum ADC value and it reduces the effects of the heterogeneities within the lesion. However, to this end, we would like to stress that average standardized uptake value (SUV) should be used instead of maximum SUV. Because the necrotic areas within the lesion have a significant impact on the average values, we believe that when the average values are used, more accurate results can be obtained with the usage of the minimum ADC and maximum SUV results, which are the indicators of the biologic characteristics of the lesion. The locations of the lesions are not specified in the article. If the lesions were in paramediastinal and paracardiac locations, cardiac and respiratory triggering images could have been obtained to ensure better imaging quality and more accurate ADC measurements. In the figures in the article, the diffusion images are presented as invert, but in the legends of the figures, they are only described as hyperintense, with no reference to their negative nature. We think that this situation may lead to confusion. In light of the article by Ohno et al. [1], in cases with progressed local non–small cell lung tumors, the ADC values obtained before and after chemotherapy and radiotherapy may be compared with PET/CT results and the response evaluated according to the Response Evaluation Criteria in Solid Tumors (RECIST). Besides, using lower b values, the vascularity of the lesion may be assessed quantitatively using DWI, and comparative examinations of DWI and PET/CT may be performed [2]. In accordance with these studies, we believe that the DWI technique may play a more important role in the evaluation and follow-up of the responses to chemotherapy and radiotherapy in patients with lung cancer. Ali Kemal Sivrioglu AKSAZ Military Hospital, Mugla, Turkey