Study of tumor motion and PTV margins using 4DCT for thorax and abdomen region

To ensure sufficient dose coverage throughout the treatment course, margins, including internal margin (IM) and setup margin (SM), should be added to the clinical target volume (CTV) to make up the planning target volume (PTV). Geometric margins to account for respiratory motion are usually derived from fluoroscopy, clinical experience, or using values reported in the literature. Such margins are neither accurate nor patient specific, allowing for the possibility of geometric miss. A geometric miss is still possible if tumor motion is greater than the assumed average motion. In addition, there can be unnecessary irradiation of normal tissue if tumor motion is smaller than expected. It is very difficult to decide margin unless we know exact motion of tumor