4D-CT Simulation using Individually Optimized Contrast Enhancement (CE): A Phantom Study

Innovation/Impact: 4D-CT simulation has been widely used to estimate the respiratory motion of lung tumors and abdominal tumors for radiotherapy planning. However, most abdominal tumors (liver, pancreas etc.) cannot be readily visualized in CT without dynamic CE. It is desirable to combine a 4D-CT without CE and a CE 3D-CT into a CE 4D-CT so that we can both visualize the tumor and estimate its motion in a single scan. Due to the very long scan time of 4D-CT (60-75 s), it is impossible to have peak CE present throughout the entire scan, therefore, one has to set a delay time between the injection of the contrast medium and the start of 4D-CT so that the CE is maximized when scanning the tumor region. In previous studies, the delay time has been set to scan the central part of the tumor at a fixed time from the injection (“A.S. Bedder, 2008, P. Mancosu, 2008”). Such fixed-timing methods did not take into consideration of the large variation in the peak CE time from one patient to another (e.g., 19 – 48 sec for the pancreatic phase, see “L. van Hoe, 1995”) and thus are not optimal for all patients. We propose to use test injection to optimize the delay time in CE 4D-CT for individual patients. To our knowledge, this is the first such study in 4DCT. In this work, we designed a phantom and demonstrated the feasibility of individually optimizing the delay time in CE 4D-CT.