Volume-of-Interest Assessment of Oncologic Response Using F-18-FDG PET/CT: A Phantom Study

The aim of this study was to evaluate the volume-of-interest (VOI) technique in the measurement of volume radioactivity and in the differentiation of necrotic sites from residual tumor activity in a phantom. Methods: PET/CT was performed on a phantom filled with F-18-FDG solution at different concentrations. The VOI was quantified in 2 sessions to evaluate the VOI measurements as a function of activity concentration in the phantom. Software was used to build the VOI, determine the volume radioactivity of the cylindric inserts (cm(3)), and compare them with their real volumes. The VOI technique was also used to discern the mixed distribution of regions of F-18-FDG activity from cold regions that represent areas of necrosis without tumor activity. Results: Volumes measured with the VOI technique were similar to the actual volumes of cylinders in the phantom (no statistical differences; P > 0.05 after t test analysis). The diameter of cold inserts correlated positively with the percentage of visualization (P < 0.01); in both sessions, it was possible to visualize 100% of the 12.7-, 11.1-, and 9.5-mm cold rods. Conclusion: VOI technique has shown great potential for evaluating volume radioactivity and differentiating hot and cold regions in a phantom; clinical studies should be performed with this technique to evaluate its utility.