The Effect of Intravenous Contrast on Photon Radiation Therapy Dose Calculations for Lung Cancer

Objective: The aim of this study was to evaluate the effect of intravenous contrast-enhanced computed tomography (CT) scans on the photon radiation dose calculations for lung cancer treatment planning. Materials and Methods: Nonionic iodinated intravenous contrast (Iohexol) was administered during the treatment planning CT scan of 9 patients with node-positive non-small-cell lung cancer (NSCLC). The potential effect of intravenous contrast was studied by changing the density of the contrast-enhanced vessels. A total of 9 patients were treated in this study: 5 patients with intensity-modulated radiation therapy (IMRT), and 4 patients with three-dimensional (3D) conformal radiation therapy. A treatment plan was generated from an unmanipulated "normal contrast" planning scan. The same planning parameters were then applied to a "no contrast" planning scan. The effect of intravenous contrast was quantified by calculating the percent change of dose in a variety of target and normal structures. To evaluate a worst-case scenario, the comparison between "normal contrast" and "no contrast" planning scans was repeated, assigning each vessel the artificial high density of 1.3 g/cm(3). Results: Dose differences between the planning image set using intravenous contrast and the image set without contrast were less than 2.5% for planning target volumes. A worst-case scenario in which normal contrast was overridden with an artificially high density of 1.3 g/cm(3) led to small dose differences of less than 3%. Conclusions: Planning lung radiation therapy treatment using CT scans that contain intravenous contrast does not result in clinically significant errors in dose delivery.