Dosimetric impact of contrast agent

It would be difficult to determine target volumes in computed tomography (CT) images for radiotheraphy (RT) treatment plan at some cases. One of the way to determine target volumes much better is using radiopque material that are called contrast agent (CA) during CT scan. However, it is thought that is going to influence the dose distribution of the plans in treatment planning system (TPS). In this context, the dosimetric impact of the contrast agent is studied in this thesis. RT treatment plans performed on CT images with and without CA to 40 patients of head and neck ca and lung ca. RT plans compared by monitor unit, maximum dose, conformity index and homogenity index parameters. Two-dimensional dose distrubition from same coronal slices of both treatment plan with and without CA were compared by gamma analysis method. RT plans with different field number, field sizes and CA concentrations were performed on solid phantom by using Three-diemensional conformal radiotheraphy (3DCRT), intensity modulated radiotheraphy (IMRT) and volume modulated radiotheraphy (VMAT) techniques. After that, measurements were performed on phantom by using ionization chamber at lineer accelerator. When lung and head and neck RT plans were examined, dosimetric impact of CA was within 2%. Gamma analysis results also support this comparison. There were seen 1% difference between solid phantom and TPS outcomes. As a result, dosimetric impact of CA remains within clinical tolerance. So it is considered that RT plans can be performed on CT images with CA.