Metabolic Tumor Volumes by [18F]-Fluorodeoxyglucose PET/CT Correlate with Occult Metastasis in Oral Squamous Cell Carcinoma of the Tongue

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Abstract
To investigate the correlation between pretreatment metabolic tumor volume (MTV) as determined by [18F]-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) and occult metastasis (OM) in oral squamous cell carcinoma (OSCC) of the tongue. Forty-three clinically node-negative (cN0) OSCC patients, diagnosed by preoperative workups (biopsy, physical examination, CT, and PET/CT) were enrolled. All patients had undergone primary tumor resections and elective neck dissections. MTVs were measured for tumors showing standardized uptake value (SUV) of >2.5 by an automated contouring program. Pretreatment variables (age, sex, clinical T stage, maximal SUV [SUVmax] and MTV) and posttreatment variables (pathologic T stage, depth of invasion, lymphovascular invasion, pathologic tumor volume, and histological differentiation) were analyzed to identify their correlation with OM. Twelve (27.9%) of 43 patients were found to have OM in pathologic specimen of neck dissections. A cutoff of 6.0 ml for the MTV was determined to be the most discriminative value for predicting OM. By univariate analysis, the patients with an MTV of >6.0 ml had significantly higher number of occult metastases than those with an MTV of ≤6.0 ml (57.1% vs. 13.7%, hazard ratio 8.33, 95% confidence interval, 1.95–35.6, P = 0.009). Lymphovascular invasion and SUVmax showed only trends toward significance (P = 0.08 and 0.05, respectively). By multivariate analysis, only MTV had a significant correlation with OM (hazard ratio 54.66, 95% confidence interval, 1.05–2842.86, P = 0.04). MTV as determined by PET/CT demonstrated a statistically significant correlation with OM in patients with cN0 OSCC of the tongue.