Tumor volume reduction rate measured during adaptive definitive radiation therapy as a potential prognosticator of locoregional control in patients with oropharyngeal cancer

Abstract

The purpose of this study was to evaluate the prognostic significance of the tumor volume reduction rate (TVRR) measured during adaptive definitive radiation therapy (RT) in patients with oropharyngeal cancer. We reviewed the RT records of 59 patients with oropharyngeal cancer who were treated with definitive RT with or without concurrent chemotherapy between January 2006 and October 2010. Adaptive replanning was performed in all patients during RT. The pre-RT and mid-RT gross tumor volumes (GTVs) of the primary and the metastatic lymph nodes were measured and analyzed for their possible impacts on locoregional control. After the median follow-up period of 41.3 months (range, 9.3-73.5 months) for survivors, there were 10 treatment failures (8 locoregional recurrences and 2 distant metastases). The locoregional control rate at 3 years in all the patients was 84.1%. The mean pre-RT and mid-RT total GTVs were 27.5 cm(3) (±17.9 cm(3) ) and 16.9 cm(3) (±12.1 cm(3) ), and the mean GTV reduction rate was 37.9% (±22.6%), respectively. The patients who achieved locoregional control had a higher TVRR than those with locoregional failure (p = .010), and those with the TVRR >35% achieved significantly higher locoregional control at 3 years (94.4% vs 72.4%; p = .018). On multivariate analysis when adjusted with other clinical prognostic factors, the TVRR was found to be a significant factor affecting the locoregional control (hazard ratio = 0.136; 95% confidence interval = 0.022-0.852; p = .033). The TVRR measured during adaptive RT proved a significant prognosticator on locoregional disease control in patients with oropharyngeal cancer, based on which a few therapeutic modifications may be considered.