Diffusion-weighted (DW) magnetic resonance imaging (MRI) for nodal staging of locally advanced head and neck squamous cell carcinoma (HNSCC): Impact on radiotherapy (RT) planning.
Authors: Piet Dirix, Vincent Vandecaveye, Frederik De Keyzer, Katya Op de Beeck, Vincent Vander Poorten, Pierre Delaere, Erik Verbeken, Luc Dirix, Robert Hermans, Sandra Nuyts
Journal: Cancer Research (2008)

3670  Purpose: With highly conformal radiotherapy (RT) techniques, such as IMRT, accurate localization of head and neck squamous cell carcinoma (HNSCC) is crucial. This pilot study prospectively examined the use of diffusion-weighted (DW) magnetic resonance imaging (MRI) for nodal staging and its impact on RT planning.  Methods: From June 2004 to April 2006, 22 patients with locally-advanced HNSCC received a contrast-enhanced CT as well as an MRI scan prior to neck dissection surgery. MRI studies consisted of both routine turbo spin-echo (TSE) sequences and DW sequences with a large range of b-values (0 to 1000 sec/mm²). After topographic correlation, lymph nodes (LN) were evaluated microscopically with prekeratine-immunostaining. An optimal apparent diffusion coefficient (ADC) threshold for discriminating between malignant and benign LN was determined. A RT planning study was performed on these surgically treated patients. One set of target volumes was designed with conventional imaging (CT and TSE-MRI) guidance only, and another with the corresponding DW-MRI images. A third set was contoured solely based on pathology results (“gold standard”).  Results: Historadiological correlation was possible in 198 LN. Using an ADC threshold of 0.00094 mm²/sec, a sensitivity of 88.9% (40/45) and a specificity of 97.4% (149/153) per LN was found for DW-MRI. The neck level staging sensitivity and specificity for DW-MRI was 93.8% (30/32) and 96.9% (93/96), respectively. DW-MRI correctly detected nodal disease in 4 patients considered N0 on conventional imaging and bilateral disease in 2 patients considered to have unilateral disease. Also, 2 patients considered to have nodal disease on conventional imaging were correctly downstaged to N0 by DW-MRI. Nodal staging agreement between imaging results and pathology findings was significantly stronger for DW-MRI (κ 0.97; 95% confidence interval (CI): 0.84 - 1.00) than for conventional imaging (κ 0.56; 95% CI: 0.16 - 0.96; p = 0.038 by McNemar’s testing). For both imaging modalities, the absolute differences in RT volumes with those obtained by pathology were calculated. Using an exact paired Wilcoxon test, the observed difference was significantly larger for conventional imaging compared to DW-MRI for nodal gross tumor volume (p = 0.0013) as well as for nodal clinical target volume (p = 0.034) delineation. Indeed, the nodal CTV was correctly changed in 8 patients (increase in 6 and decrease in 2 patients). In 2 patients, the nodal CTV was overestimated based on DW-MRI; no underestimation of the target volumes occurred.  Conclusion: These findings suggest that DW-MRI is superior to conventional imaging for pre-RT nodal staging of HNSCC, with an important potential impact on organ-sparing and disease control. Confirmatory trials should be initiated, preferably in comparison with FDG-PET/CT.