Diffusion weighted magnetic resonance imaging of pre and post treatment nasopharyngeal carcinoma

Objectives: To evaluate the utility of different Apparent Diffusion Coefficient (ADC) values on Diffused Weighted Magnetic Resonance Imaging (DW-MRI) for nasopharyngeal carcinoma (NPC). Study design and setting: A retrospective cohort study in a single tertiary medical center. Subjects and methods: The study group consists of patients with pathology proven NPC that underwent DW-MRI prior or/and following a non-surgical chemo radiation treatment between the years 2007 and 2017. ADC thresholds were analyzed and compared for primary (pre-treatment) and expected post-irradiation NPC cases and healthy controls. Results: We recruited 144 patients who underwent 195 MRI's for NPC. 25 DW-MRI were performed before (primary, active NPC) and 56 following (no residual NPC) treatment. 45 out of 225 patients who had brain DW-MRI for other reasons (control group) had measurable nasopharynx tissue (N = 33, adjusted for age and gender). The mean ADC of NPC prior to treatment (0.69 ± 0.13 × 10⁻³ mm²/s) was significantly lower (ANOVA, P < 0.001) compared to the mean ADC of the adjusted controls (1.11 ± 0.25 × 10⁻³ mm²/s) and post-treatment (1.49 ± 0.28 × 10⁻³ mm²/s) groups. An ADC threshold of 0.805 × 10⁻³ mm²/s had 94% and 93.9% sensitivity and specificity rates, respectively and an odds ratio of 175[95%CI(23.25–1000)], comparing ADC levels of pre-treatment NPC patients and adjusted control group. An ADC threshold of 0.965 × 10⁻³ mm²/s yielded 100% positive and negative predicted values distinguishing pre-treatment and post-treatment NPC patients (free of disease). There was no statistical association between ADC levels and tumor volume/stage, nodal stage or group staging. Conclusions: ADC levels have distinct values in newly diagnosed and follow up of NPC.