Metabolic tumor volume and conformal radiotherapy based on prognostic PET/CT for treatment of nasopharyngeal carcinoma

For patients with nasopharyngeal carcinoma (NPC), prognostic indicators to customize subsequent biologically conformal radiation therapy may be obtained via 2-(fluorine-18)-fluoro-2-deoxy-D-glucose ((18)F-FDG) positron emission tomography/computed tomography (PET/CT). This retrospective study assessed the prognostic significance and feasibility of conformal radiotherapy for NPC, based on (18)F-FDG PET/CT. Eighty-two patients with NPC underwent (18)F-FDG PET/CT prior to intensity-modulated radiation therapy (IMRT). The maximum standardized uptake value (SUV(max)) and metabolic tumor volume (MTV) of the primary tumor were measured, with MTV(x) based on absolute SUV(x) values ≥ specific threshold x on each axial image. The cut-off SUV(max) and MTV values for predicting 3-year progression-free survival (PFS) were calculated according to a receiver operating characteristic curve. Assessed were correlations between SUV(max) and MTV and between threshold x and MTV(x), and the MTV percentage of the primary tumor volume at threshold x. The SUV(max) and MTV were positively associated, as were MTV and primary tumor volume. Primary tumor volume, SUV(max), and MTV were significant predictors of survival. The 3-year PFS rates for SUV(max) ≤8.20 and >8.20 were 91.1% and 73.0%, respectively (P = .027). With furthermore analysis, patients having tumor with smaller MTV had higher 3-year PFS than patients having tumor with larger MTV. The 3-year PFS rate was inversely related to MTV. SUV(max) and MTV, derived by PET/CT, are important for assessing prognosis and planning radiotherapy for patients with NPC. Small MTV indicated better 3-year PFS compared with large MTV. For the best therapeutic effect, MTV(4.0) was the best subvolume to determine radiotherapy boost.