ABSTRACT:The metabolic tumor volume (MTV) is the volume of metabolically-active tumor on PET/CT. Although its potential clinical value has been investigated in many cancers, its routine use has been hampered by the delineation method used to calculate the tumor volume. This may be especially difficult for fuzzyPET images. Previous studies have used a lot of approaches for delineation of tumor volume; however, still there is no clear consensus on which method to be used, especially in the oral cavity region where the contouring may be difficult due to variable grades of physiological FDG uptake. Theaim of this study is to determine best contouring method for the metabolic tumor volume from PET/CT using different absolute and relative SUV values with correlation to the pathology. Materials and methods:We prospectively studied 126 patients with oral cavity squamous cell carcinoma (OCSCC) who underwent PET/CT before definitive treatment by radical surgery. The metabolic tumor volume (MTV) was calculated for the primary tumor according to absolute SUV figures (2.5, 3.0, 3.5 & 4.0) and fixed percentage of SUVmax (30%, 40%, 50%, 60% & 70%). Correlation between the axial diameters generated from these methods and the axial diameter from the fixed pathology specimens was used to determine the best of these methods. Results: Overall among the 9 contouring methods, absolute SUV 3.0 gave the best correlation (R = 0.723; P < 0.001). Among the methods based on fixed percentage of SUVmax, a threshold of30% gave the best correlation (R = 0.701; P <0.001) Conclusion: Contouring the metabolic tumor volume based on absolute SUV 3.0 can be used to represent the best correlation with pathologic data in patients with OCSCC.
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