Prediction of Local Failures with a Combination of Pretreatment Tumor Volume and Apparent Diffusion Coefficient in Patients Treated with Definitive Radiotherapy for Hypopharyngeal or Oropharyngeal Squamous Cell Carcinoma

Purpose: The purpose of this study was to investigate the clinical factors for predicting local failure after definitive radiotherapy in oropharyngeal or hypopharyngeal squamous cell carcinoma. Materials and Methods: Between July 2006 and December 2008, 64 consecutive patients with squamous cell carcinoma of the hypopharynx or the oropharynx treated with definitive radiotherapy were included in this study. Clinical factors, such as pretreatment hemoglobin (Hb) level, T-stage, gross tumor volume of primary tumors (pGTV), and maximum standardized uptake value (SUVmax) on FDG-PET, were evaluated for the correlation with local failure. A subset analysis of 32 patients with MR images including diffusion-weighted images (DWI) as a pretreatment evaluation was also performed. The Kaplan-Meier curves, the log-rank test, and the Cox proportional hazards model were used to evaluate these clinical factors. Results: Eleven of 64 patients experienced local recurrence, with a median follow-up time of 15 months. In the univariate analysis, Hb level (p = 0.0261), T-stage (p = 0.012), pGTV (p = 0.0025), and SUVmax (p = 0.024) were significantly associated with local failure. In the multivariate analysis, pGTV (p = 0.0070) remained an adverse factor for local control. In the subset analysis of 32 patients with DWI, the median apparent diffusion coefficient (ADC) value of primary tumors on DWI was 0.79 x 10(-3) mm(2)/s (range, 0.40-1.60 x 10(-3) mm(2)/s). Patients with a high ADC value (> 0.79 x 10(-3) mm(2)/s) had a significantly lower local control rate than patients with a low ADC value (100% vs. 44%, p = 0.0019). The rate of local failure among patients with a large pGTV and a high ADC value was 55% (6/11), whereas no local failures occurred (0%, 0/21) among patients with a small pGTV or a low ADC. Conclusions: These results suggest that a combination of a large tumor volume and a high ADC value could be predictive of local recurrence after definitive radiotherapy in hypopharyngeal or oropharyngeal squamous cell carcinoma.