In the context of oropharyngeal cancer treated with definitive radiotherapy, the aim of this retrospective study was to identify the best threshold value to compute metabolic tumor volume (MTV) and/or total lesion glycolysis to predict local-regional control (LRC) and disease-free survival.
One hundred twenty patients with a locally advanced oropharyngeal cancer from 2 different institutions treated with definitive radiotherapy underwent FDG PET/CT before treatment. Various MTVs and total lesion glycolysis were defined based on 2 segmentation methods: (i) an absolute threshold of SUV (0–20 g/mL) or (ii) a relative threshold for SUVmax (0%–100%). The parameters’ predictive capabilities for disease-free survival and LRC were assessed using the Harrell C-index and Cox regression model.
Relative thresholds between 40% and 68% and absolute threshold between 5.5 and 7 had a similar predictive value for LRC (C-index = 0.65 and 0.64, respectively). Metabolic tumor volume had a higher predictive value than gross tumor volume (C-index = 0.61) and SUVmax (C-index = 0.54). Metabolic tumor volume computed with a relative threshold of 51% of SUVmax was the best predictor of disease-free survival (hazard ratio, 1.23 [per 10 mL], P = 0.009) and LRC (hazard ratio: 1.22 [per 10 mL], P = 0.02).
The use of different thresholds within a reasonable range (between 5.5 and 7 for an absolute threshold and between 40% and 68% for a relative threshold) seems to have no major impact on the predictive value of MTV. This parameter may be used to identify patient with a high risk of recurrence and who may benefit from treatment intensification.
From the *Department of Radiation Oncology, Lausanne University Hospital, Switzerland; †INSERM, U1099, Rennes; ‡Université de Rennes 1, LTSI, Rennes, France; §Ecole Polytechnique Fédérale de Lausanne, Lausanne; and ∥University of Applied Sciences Western Switzerland, Sierre, Switzerland; ¶University Hospital Jean Minjoz, INSERM 1098, Besancon; **Nuclear Medicine Department, Centre Eugene Marquis, Rennes; ††Department of Radiation Oncology, Centre Eugene Marquis, Rennes; and ‡‡Nuclear Medicine and Molecular Imaging Department, Lausanne University Hospital, Lausanne, Switzerland.
Received for publication October 20, 2016; revision accepted January 15, 2017.
Conflicts of interest and sources of funding: This work was partly supported by the Swiss National Science Foundation with grant agreement PZ00P2_154891 (to A. Depeursinge). None declared to all other authors.
Correspondence to: Joël Castelli, MD, MSc, Department of Radiation Oncology, Centre Eugene Marquis, avenue de la Bataille Flandre Dunkerque, F-35000 Rennes, France. E-mail: firstname.lastname@example.org.