Impact of Intravenous Contrast on Dose Calculations in Carcinoma Esophagus Using Monaco Treatment Planning System

A BSTRACT Introduction: Planning target volumes (PTV) along with critical structures, like organs at risk (OAR), are defined by high-quality computed tomography (CT) imaging, which is essential for accurate radiotherapy treatment planning. CT scans provide essential tissue density data, crucial for dose calculation algorithms. However, artifacts from high-density materials and contrast agents can compromise CT imaging. Depending on CT scanner being utilized, each treatment planning system (TPS) must precisely convert Hounsfield Units to electron density. Aims and Objectives: This study aims to compare dose calculations between contrast-enhanced CT (CE-CT) images and plain CT images in cases of esophageal carcinoma using the Monaco TPS. Materials and Methods: Thirty patients having mid to lower third esophageal carcinoma, with or without the gastroesophageal junction, who required radical radiation therapy, were included. During CT simulation, plain and CE-CT images were obtained for every patient. Two contour plans were generated: one with contrast enhancement (in the heart and abdominal aorta) and another without. Dose differences were evaluated and treatment plans were developed by employing the Monaco TPS. Results: The study found dose variations of 1.58% in the PTV, 2.16% in the heart, 2.82% in the spinal cord, 2.36% in the right lung, and 3.52% in the left lung, with statistical significance, with P = 0.0056, 0.0033, 0.025, 0.029, and 0.011, respectively. Conclusion: Intravenous contrast in planning CT images significantly impacts dose calculations for the PTV and OARs. The study suggests using plain CT as the primary imaging set for delineation or adopting advanced features like Force Electron Density could be an alternative for CE-CT users. A larger clinical dataset is needed to validate these findings, and a dosimetric model to explain this phenomenon would be beneficial.