Evaluation of a Treatment Planning System for Applying the Effect of Titanium Clips on Isodosedistribution in Radiation Therapy of Colorectal Cancer

Background: In laparoscopy of colorectal tumors, titanium clips are used to close the surgery site. For post-operation treatment with radiation, the clips might change the dose distribution. In this study, the effect of titanium clips in isodose distribution of 6- and 18-MV photons was evaluated. Methods: Laparoscopy clips were placed on a phantom with material close to soft tissue. Computed tomography (CT) scan images of this phantom were imported in planning software and the percentage depth dose (PDD) and profiles of the dose were obtained for 6- and 18-MV photons. Findings: Calculated PDD showed weakening and backscattering of the dose of radiation in the path after the clips. Dose changes for the regions after the clips had a maximum of 1.7% and 1.1% for 6- and 8-MV photons, respectively. The amount of backscattering was up to 0.4% and 0.7% for 6- and 18-MV photons, respectively. Conclusion: Presence of the titanium clips in the path of radiation changes the depth dose and profiles. The changes for of a single clip are minor. However, for few clips beside each other, the effect of radiation attenuation is not negligible.