The Effect of Contrast Media on Treatment Planning and Dose Calculation in Radiation Therapy of Pelvis Cancers

Using contrast media is very important in diagnosis and identification of organ from the surrounding tissue. Contrast media can alter radiation absorption of studied organs following by enhanced image contrast. This study aimed to assess the influence of contrast media on treatment planning and dose calculation in radiation therapy of pelvic cancers.
Six patients with pelvic area cancer with two sets of computed tomography (CT) images, one with contrast media and another without it, were studied and the effects of contrast media were studied.
Findings: After using contrast media, an increase of 2.91% in monitor unit (MU) for right lateral (RL) field and decreases of 0.59%, 0.75%, and 1.47% in monitor unit anterior-posterior (AP), posterior-anterior (PA), and left lateral (LL) fields was obtained in rectum cancer, respectively. For bladder cancer, a decrease of 0.34% in monitor unit for AP filed and increases of 1.57%, 0.46%, and 0.39% in monitor unit for PA, RL and LL fields was calculated, respectively. For cervix cancer, a decrease of 1.1% for AP field and an increase of 0.68% for PA field were obtained.
Regarding dose-volume histograms (DVHs) and calculated monitor units, the results showed that the dose differences between the plans for the CT images with and without contrast media were less than 1%. Of course to ensure the effect of contrast media on the amount of delivered dose to the target organ, study on more patients is recommended.