Definition of tumor volumes based on FDG, PET-CT, based on SUV values in non-small cell lung cancer: Comperative sampling study of CT and pathological volumes

The aim of the 3D conformal radiotherapy is to have the desired dose on target volume while keeping the healthy tissue dose at minimum. The definition of target volumes by the treating physicians has been found to bear the largest source of error in the whole chain of radiotherapy. That requires the best methodology for volume determination.In this study, 13 patients were randomly selected (12 male, 1 female; average age :68) with early stage non small cell lung cancer had pre-operative PET-CT imaging for staging and performed surgery. On PET images different volume determination methods used based on standardized uptake (SUV) value thresholds (SUV20, SUV30, SUV40, SUV50, SUV20BG, SUV40BG, SUV50BG, SUV2.5, SUV3.5). Determined volumes (GTV20, GTV30, GTV40, GTV50, GTV20BG, GTV40BG, GTV50BG, GTV2.5, GTV3.5) are compared with pathological volumes (GTVpat), volumes determined by CT images (GTVBT) are compared with PET volumes.A relation between GTVBT, the GTVs determined by PET images and GTVpat analyzed using three different statistical approach.Results of the study showed that GTVBT has the highest similarity with GTVpat. Using regression analyses, optimum SUV threshold is calculated. SUVmax related optimum SUV threshold is resulted as; SUVopt%=41.67 (±%12.66), Constant SUV threshold is resulted as; SUVopt=3.83(±1.52). However pathological volumes have no correlation with constant SUV values. Hence it?s concluded that using constant SUV values to determine tumor volumes cannot be a standard method.