Use of diffusion-weighted magnetic resonance imaging in cervical lymph node metastasis from nasopharyngeal carcinoma receiving intensity modulated radiation therapy

Objective: To investigate the value of diffusion-weighted magnetic resonance imaging (DWI) and apparent diffusion coefficients (ADC) in detecting metastatic lymph nodes from nasopharyngeal carcinoma (NPC), and predicting the response of these nodes to concurrent chemoradiation (CRT). Methods: Eighteen patients with pathologically proven NPC received conventional magnetic resonance imaging (MRI) and DWI before treatment,weekly during treatment, and one month after treatment.DWI was performed using a single-shot echo-planar (SSEPI) MR imaging sequence with b values of 0 and 1500 s/mm². ADC maps were reconstructed for all patients and ADC values were calculated for each lymph node and tongue muscle. Totally fifty-two morphologically abnormal lymph nodes were analyzed. The ADC values of the metastatic lymph nodes before treatment were compared between those with the short axis ≥10 mm (n=32) and those with the short axis <10 mm (n=20), and the dynamic changes in ADC values of the lymph nodes before, during, and after therapy were observed and recorded. Results: The average ADC of the 32 lymph nodes with the short axis ≥ 10 mm was (0.71±0.12)×10^-3mm/s, not significantly different from that of the 20 lymph nodes with the short axis < 10 mm [(0.73±0.16)×10^-3mm/s, t=1.11, P=0.27]. The average ADC values of these lymph nodes before treatment was significantly lower than that of the tongue muscle (t=19.35, P<0.0001). During CRT, the ADC values of the lymph nodes increased gradually,with the most evident change in the first two weeks before reaching a relatively flat plateau thereafter. The ADC value of the residual lymph nodes after CRT was significantly higher than that before treatment (t=12.72, P<0.0001), however, not statistically significant different from that of the normal tongue muscle (t=0.34, P=0.73). Conclusions: DWI plays an important role in diagnosing the metastatic lymph nodes from NPC and is feasible for observation of the early response of the lymph nodes to IMRT, thus helping the clinicians make appropriate treatment planning and replanning in the course of radiotherapy. (authors)