Evaluation of quantitative imaging parameters in head and neck squamous cell carcinoma

Functional imaging such as 18F-fluoro-deoxy-glucose positron emission tomography/computed tomography (FDG-PET/CT), 18F-fluoro-misonidazole (F-MISO)-PET/CT, and diffusion-weighted magnetic resonance imaging (DW-MRI) can assess complex biological phenomena in tumors reflecting underlying disease biology. The aim of this prospective observational study was to correlate quantitative imaging parameters derived from pretreatment biological imaging such as FDG-PET/CT, F-MISO-PET/CT, and DW-MRI with each other and with clinical outcomes in patients with head and neck squamous cell carcinoma (HNSCC) treated with definitive radio(chemo)therapy.

Twenty patients with pharyngo-laryngeal cancers underwent pretreatment biological imaging. Gross tumor volume (GTV) was delineated on axial planning CT (GTVCT). Quantitative FDG-PET/CT parameters included maximum, mean, minimum standardized uptake values (SUVmax-FDG, SUVmean-FDG, SUVmin-FDG); metabolic tumor volume (MTV); and total lesion glycolysis (TLG). F-MISO-PET/CT parameters included hypoxic tumor volume (HTV); maximum, mean, minimum SUV; and fractional hypoxic volume (FHV). Mean apparent diffusion coefficient (ADCmean) was derived from DW-MRI.

There was moderately strong positive correlation (r=0.616, P=0.005) between GTVCT and MTV. HTV derived from F-MISO-PET/CT at 3-hours (HTV3hrs-F-MISO) showed strong positive correlation with GTVCT (r=0.753, P<0.0001) and MTV (r=0.796, P<0.0001) respectively. ADCmean showed strong positive correlations with SUVmean-5hrs-F-MISO (r=0.713, P=0.021) and SUVmin-5hrs-F-MISO (r=0.731, P=0.016) respectively. A moderate negative correlation (r=-0.500, P=0.049) was observed between ADCmean and MTV. At a median follow up of 44 months, the 5-year Kaplan-Meier estimates of loco-regional control, disease-free survival, and overall survival were 53%, 43%, and 40% respectively. Larger volume of primary tumor (GTVCT>22cc and MTV>7.9cc) and increasing hypoxia (HTV3hr-F-MSO>4.9cc) were associated with worse outcomes.

Functional imaging represents an attractive and non-invasive modality to assess complex biological phenomena in solid tumors. Larger tumor volume and increasing hypoxia emerged as putative prognostic imaging biomarkers in HNSCC.