The effect of CT contrast agents on treatment planning and dose calculation in radiation therapy of pelvis cancers

Introduction: Using contrast medium in diagnosis and identifying of an organ from its surrounding tissue is very useful. These contrast mediums alter radiation absorption of studied organs. The aim of this study is to identify the influences of contrast media in treatment planning system of the pelvis.   Materials and Methods: Seven patients with pelvis area cancer with two sets of CT image, one with contrast medium and another without it, have been used and influences of contrast medium in treatment planning system for these patients were studied.   Results: After using contrast medium 2.63% increase in MU for RL field and 0.79%, 1.05%, 1.42% decrease in MU for AP, PA, RL fields have been obtained in rectum, respectively. For Bladder cancer, 0.34% decrease in MU of AP filed and 1.57%, 0.46%, 0.39% increase in MU for PA, RL and LL fields have been calculated, respectively. For cervix cancer, 1.1% decrease for AP field and 0.68% increase for PA field have been obtained. Conclusion: According to the DVHs and calculated MUs, the results showed that the dose differences between the plans for the CT images with and without contrast medium were less than about 1% and was clinically tolerable.