Dose painting in radiotherapy for head and neck squamous cell carcinoma: value of repeated functional imaging with (18)F-FDG PET, (18)F-fluoromisonidazole PET, diffusion-weighted MRI, and dynamic contrast-enhanced MRI.

Abstract

The purpose of this work was to evaluate the potential of functional imaging with (18)F-FDG PET, (18)F-fluoromisonidazole PET, diffusion-weighted MRI, and dynamic contrast-enhanced MRI to provide an appropriate and reliable biologic target for dose painting in radiotherapy for head and neck squamous cell carcinoma (HNSCC). Fifteen patients with locally advanced HNSCC, treated with concomitant chemoradiotherapy, were prospectively enrolled in a bioimaging protocol. Sequential PET ((18)F-FDG and (18)F-fluoromisonidazole) and MRI (T1, T2, dynamic enhanced, and diffusion-weighted sequences) were performed before, during, and after radiotherapy. Median follow-up was 30.7 mo (range, 6.3-56.3 mo); in 7 patients, disease recurred. Disease-free survival correlated negatively with the maximum tissue-to-blood (18)F-fluoromisonidazole ratio (T/B(max)) on the baseline (18)F-fluoromisonidazole scan (P = 0.04), with the size of the initial hypoxic volume (P = 0.04), and with T/B(max) on the (18)F-fluoromisonidazole scan during treatment (P = 0.02). All locoregional recurrences were within the (18)F-FDG-avid regions on baseline (18)F-FDG PET; 3 recurrences mapped outside the hypoxic volume on baseline (18)F-fluoromisonidazole PET. Lesions (primary tumor and lymph nodes) where a locoregional recurrence developed during follow-up had significantly lower apparent diffusion coefficients on diffusion-weighted MRI during week 4 of radiotherapy (0.0013 vs. 0.0018 mm(2)/s, P = 0.01) and at 3 wk after treatment (0.0014 vs. 0.0018 mm(2)/s, P = 0.01) and a significantly higher initial slope on baseline dynamic enhanced MRI (26.2 vs. 17.5/s, P = 0.03) than did lesions that remained controlled. These results confirm the added value of (18)F-FDG PET and (18)F-fluoromisonidazole PET for radiotherapy planning of HNSCC and suggest the potential of diffusion-weighted and dynamic enhanced MRI for dose painting and early response assessment.