SU‐GG‐J‐166: Reduction of Motion Artifacts Occurring at the Lung/diaphragm Interface Using 4D‐CT Attenuation Correction On 4D‐PET Scans: Implications for Radiation Therapy Planning

Abstract

Purpose: For PET/CT the fast CT acquisition time can lead to errors in attenuation correction, particularly at the lung/diaphragm interface. Gated 4D‐PET can reduce motion artifacts, though it is not always attenuation corrected with a similarly acquired 4D‐CT. We performed phantom studies specifically designed to evaluate 4D‐PET images using three different methods for attenuation correction: a single 3D‐CT (3D‐CTAC), an averaged 4D‐CT (CINE‐CTAC), and a fully phase matched 4D‐CT (4D‐CTAC). Method and Materials: A phantom was designed with two density regions corresponding to diaphragm and lung. An 8ml vial loaded with FDG was used to represent a lung tumor and background FDG was also added with an 8:1 ratio. Imaging was performed with a GE Discovery DVCT‐PET/CT scanner. Periodic motion of 2 cm amplitude was used and the image data was reconstructed into 10 phase bins over the motion cycle. Image data was analyzed using a GE image processing workstation and in‐house developed software. Values of activity within the target for each relative phase were corrected for decay and compared to those derived from a 3D PET scan with no motion present (3D‐STATIC). Results: Activity values derived from 4D‐CTAC corrected PET images are generally closer to 3D‐STATIC images with no motion present. Mean activity over the known target volume over the motion cycle, normalized to the activity for 3D‐STATIC, was 93%, 101% and 98% for 3D‐CTAC, CINE‐CTAC and 4D‐CTAC images respectively with corresponding standard deviations of 6%, 10% and 3%. Conclusion: Compared to other attenuation correction methods, 4D‐CTAC corrected 4D‐PET images correspond more closely on average to similar 3D‐STATIC images. Using CINE‐CTAC for correction resulted in mean activity values slightly closer to 3D‐STATIC, but with much greater variation over the motion cycle. We believe these results have implications for the use of 4D‐PET imaging for radiation therapy target definition.