The Effect of Contrast Material in Three Dimensional Conformal and Helical Treatment Plans in Rectal Radiotherapy

The aim of this study to investigate the impact of contrast agent used for imaging purposes in the treatment of neoadjuvant rectal cancer patients. In rectal radiotherapy, contrast agent is used during the treatment simulation but the patient treated without contrast. In our study, we will examine whether CTs taken with contrast agent are sufficient for clinical application. A total of eighteen patients who had undergone neoadjuvant treatment with rectal cancer randomly selected. Two different CT scans were performed for each patient. The contours were delineated on a non-contrast CT images with the help of image fusion with contrast CT images. Then, the contours drawn on the non-contrast CT were copied to the contrast-enhanced CT with the help of fusion to be used in contrast CT plans for our retrospective study. Subsequently, all plans were generated in Eclipse TPS and Accuray Precision TPS. Finally the plans with contrast agent and non-constrat agent were compared. 3DCRT plans were compared for contrast and non-contrast images, no significant differences were observed in either the PTV or the maximum and mean values of critical organs. It was observed that the average post-contrast doses increased significantly for small bowel only in helical therapy (p = 0.019). As a result, no significant difference was observed in terms of PTV and critical organs in the comparison of 3DCRT plans. In the comparison of helical plans, there was only a significant difference in the bladder. Based on these results, we suggest that planning can be done with a single contrast CT for 3DCRT treatments, both to avoid further discomfort for the patient and to prevent additional tomography doses. On the other hand, for helical therapy, we believe that it can be clinically evaluated whether the treatment will be performed with contrast CT depending on the patient's condition.