Quantifying ITV instabilities arising from 4DCT: A simulation study using patient data

摘要

Treatment planning for patients undergoing radiation therapy is often performed based on four dimensional computed tomography (4DCT) when respiratory motion is present, as in lung cancer patients. 4DCT is used to define the internal target volume (ITV) that, ideally, incorporates all potential locations of the tumour. In this work, we use the locations of gold fiducial markers implanted in lung tumours of 8 patients to represent tumour motion. These fiducial locations are used in a simulation of a four slice CT scanner to generate the ITV for 10 mm, 20 mm and 30 mm diameter model tumours. To demonstrate instabilities in the ITV definition based on 4DCT, the ITV calculation was repeated for the same patients for consecutive scan start times, staggered by one second. The percent difference in the ITV and the percent of time that the ITV contains the tumour are both evaluated. The ITV from a single patient was found to vary by >46% – 127% for a tumour diameter of 10 mm. The ITV did not cover the entirety of the tumour >11%–74% of the time for a 10 mm tumour diameter.