Abstract 4296: Correlation of the apparent diffusion coefficient of water assessed by diffusion-weighted imaging with treatment outcome in refractory lymphoma patients
Authors: Arias-Mendoza Fernando , Mojahed Hamed , Sawas Ahmed , O'Connor Owen A. 
Published: May 2015

Abstract
The contrast of MR images can be made sensitive to the average motion of water molecules (diffusivity) giving rise to diffusion-weighted imaging (DWI). Intensity maps of the apparent diffusion constant (ADC) of water can be generated from the DWI information and average ADC values of anatomical regions can be assessed. Malignant tissues generally exhibit hypercellularity, increased nucleus-to-cytoplasm ratios, and an increased amount of macromolecules resulting in decreased water diffusivity (lower ADC). Additionally, a response-related ADC increase has been demonstrated in malignancies under therapy. We previously reported that the ADC mean value (in 10-3 mm2 s-1 [SD, n]) of masses of refractory lymphoma patients prior to a new treatment was lower than the ADC mean value of lymph nodes of healthy volunteers (0.91 [0.23, 15] vs. 1.13 [0.14, 10], respectively). This difference was significant (p &lt; 0.01) despite of a large dispersion on the ADC data from the patients. Given this dispersion, we wanted to prove if refractory lymphoma patients with lower ADC values responded differently than those with higher ADC values. Experimental Design: Under ethical review board approval, refractory lymphoma patients underwent a pretreatment MR exam. DWI was acquired using echo-planar imaging with fat suppression and b-values of 0 and 1000 s/mm2 and the ADC of water in the tumor obtained. Time to treatment failure (TTF) was defined as the time between the end of one treatment and the start of a new one. Results: ADC and TTF were obtained in 12 refractory lymphoma patients and divided into those with TTF ≤ 75 days and those with TTF &gt; 75 days. The ADC mean value [SD, n] in patients with TTF ≤ 75 days was 0.73 [0.20, 5] while in those with TTF &gt; 75 days was 1.04 [0.20, 7]. These mean values were significantly different (p &lt; 0.02). Furthermore, the comparison of the ADC mean value of lymph nodes of healthy volunteers with the ADC mean value of refractory patients with TTF ≤ 75 days was highly significant (p &lt; 0.0005) while the comparison between healthy volunteers and patients with TTF &gt; 75 days was not. Discussion: Our results demonstrate that refractory lymphoma patients with tumor masses displaying abnormally low ADC values prior to the start of treatment have poorer treatment outcome than those patients with ADC tumor values that are comparable to those in normal lymph nodes. If low ADC is due to increased tumor cellularity in patients with poorer outcome, this could produce reduced drug availability, thus explaining the substandard outcome. Our results demonstrate an important predictive value of the ADC determination by DWI in refractory lymphoma patients. This together with the fact that DWI is a noninvasive technique and its acquisition is fairly quick makes the ADC a parameter that could become critical for the clinical examination of the patient with refractory lymphoma.
Citation Format: Fernando Arias-Mendoza, Hamed Mojahed, Ahmed Sawas, Owen A. O'Connor. Correlation of the apparent diffusion coefficient of water assessed by diffusion-weighted imaging with treatment outcome in refractory lymphoma patients. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4296. doi:10.1158/1538-7445.AM2014-4296