Impact of contrast agents on organ dosimetry in pediatric diagnostic fluoroscopy: the voiding cystourethrogram

<i>Objective.</i>International Commission on Radiological Protection (ICRP) Task Group 113 is developing reference values of organ and effective dose coefficients (DCs) for radiography, fluoroscopy, and computed tomography imaging exams. In support of these efforts, our focus is on pediatric diagnostic fluoroscopy. Contrast agents used during clinical examinations are an important consideration of the work undertaken by the Task Group. This work demonstrates the importance of including organ contrast volume concentrations for the calculation of reference organ DCs in the voiding cystourethrogram (VCUG).<i>Approach.</i>The ICRP newborn and 15 year female reference phantoms were utilized within the Particle and Heavy Ion Transport code system for the calculation of organ DCs. A pediatric radiologist with over 30 years of clinical experience defined the imaging fields for a VCUG examination consistent with clinical practice. Of these, four imaging fields were selected for investigation. The transport simulations modeled an iodinated contrast solution similar to Bracco Group's 18% weight per volume, cystografin diatrizoate meglumine and typical bladder content was supplemented to make up the remainder volume. Iodinated contrast volumes of 0%, 25%, 50%, 75%, and 100% concentration by volume were modeled and associated DCs for in-field organs were computed.<i>Main results.</i>Organ DCs were calculated for the urinary bladder wall, colon wall, ovaries, and uterus for both female phantoms under irradiation geometries representative of a VCUG examination. Some organ DCs increased with iodine volume in the bladder and other organ DCs decreased as the iodine contrast volume completely filled the bladder (100%).<i>Significance.</i>The study results demonstrate for the newborn phantom percent differences in organ DCs varied between 0%-10% for the organs of interest, while they varied between 0%-22% in the 15 year phantom suggesting the importance of including contrast media in Monte Carlo radiation transport simulations of the VCUG examination.