Defining gross tumor volume using positron emission tomography/computed tomography phantom studies

Tumor volume and standard uptake value (SUV) calculated from positron emission tomography/computed tomography (PET/CT) images differ from their real values. Besides errors introduced by scintillation materials, photomultiplier tubes, and image reconstruction algorithms, measurements are affected by patients´ prostheses, body movements, and body shape. To address these problems, we calculated tumor volume and SUV using the standard phantom (PET Phantom-NEMA IEC/2001) and obtained calibration constants. We found that while tumor volume increases with increasing SUV and tumor diameter, it also increases with increasing SUV and decreasing tumor diameter. Conversely, tumor volume decreases with decreasing SUV and tumor diameter and with decreasing SUV and increasing diameter. These results suggest that a correction factor should be applied to SUV and tumor volume obtained from PET/CT images.