SU‐GG‐I‐07: Evaluation of Cine‐CT for Quantifying Respiratory Displacement of Lung Tumors Without a Respiratory Surrogate

Purpose: The conventional approach to measuring tumor displacement, the net movement of its geometric center, is to use 4D‐CT with a respiratory surrogate. We propose using the MIP, average CT and new Max‐Min projection CT images from cine‐CT without a respiratory surrogate as a method of evaluating respiratory displacement of lung tumors. We evaluate the reliability of this method in producing accurate displacement quantification. Method and Materials: We design a new Max‐Min projection CT image, which is the pixel‐by‐pixel average of the maximum intensity projection (MIP) and minimum intensity projection (mip.) The Max‐Min directly shows the displacement volume of a tumor. A simple distance measurement on Max‐Min yields the tumor displacement. Max‐Min, cine‐MIP and cine‐ACT are obtained on a scanner with the cine‐CT capability without using a respiratory surrogate. The average CT (ACT) images are derived from averaging the cine CT images at the same slice location. All cine‐CT images are acquired on a GE 8‐slice CT. We use Max‐Min, cine‐MIP and cine‐ACT images to measure the tumor displacement for 38 4D‐CT simulation patients with lung tumors. For comparison, the 4D‐CT scan of each patient is also used to measure displacement. Results: The Max‐Min images show a clear displacement volume and yield a measurable displacement in 76.3% of cases. The Max‐Min method works best for tumors with reasonably smooth boundaries and displacements less than the tumor size. With 4D‐CT as a gold standard, Max‐Min measures displacement accurately to within one CT voxel (2.5 mm). In the other 23.7% of cases, cine‐MIP and cine‐ACT are used to quantify the displacement with 5 mm accuracy (2 CT voxels). Conclusion: Use of the Max‐Min, cine‐MIP and cine‐ACT images is a reliable method of quickly quantifying tumor respiratory displacement without a respiratory surrogate.