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

Abstract

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 (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 F-FDG PET/CT. Eighty-two patients with NPC underwent F-FDG PET/CT prior to intensity-modulated radiation therapy (IMRT). The maximum standardized uptake value (SUVmax) and metabolic tumor volume (MTV) of the primary tumor were measured, with MTVx based on absolute SUVx values ≥ specific threshold x on each axial image. The cut-off SUVmax and MTV values for predicting 3-year progression-free survival (PFS) were calculated according to a receiver operating characteristic curve. Assessed were correlations between SUVmax and MTV and between threshold x and MTVx, and the MTV percentage of the primary tumor volume at threshold x. The SUVmax and MTV were positively associated, as were MTV and primary tumor volume. Primary tumor volume, SUVmax, and MTV were significant predictors of survival. The 3-year PFS rates for SUVmax ≤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. SUVmax 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, MTV4.0 was the best subvolume to determine radiotherapy boost.

Figure 1

The percentage of primary tumor volume that constitutes the MTV. As the threshold increases, the area of the MTV within the PTV decreases. However, the change in MTVs above a threshold of 4.0 is not significant. MTV = metabolic tumor volume, PTV = primary tumor volume.

Figure 2

The ROC curve was used to determine the appropriate cut-off point of SUV_max, PTV, and MTVs at thresholds 2.5–6.0. MTV = metabolic tumor volume, PTV = primary tumor volume, ROC = Receiver operating characteristic, SUV = standardized uptake value.

Figure 3

The PFS curves for SUV_max ≤8.20 and >8.20. PFS = progression-free survival, SUV = standardized uptake value.

Figure 4

The PFS curves for PTV ≤48.70 mL and >48.70 mL measured by MRI. MRI = magnetic resonance imaging, PFS = progression-free survival, PTV = primary tumor volume.

Figure 5

The PFS curves for MTV_4.0 ≤5.73 mL and >5.73 mL. MTV = metabolic tumor volume, PFS = progression-free survival.