Validating The University Of Florida/National Cancer Institute Family Of Hybrid Computational Pediatric Phantoms For Cardiac Fluoroscopic Studies

Date(s) - 07/02/2015
3:00 pm - 5:00 pm

Emily Marshall, MS student

With yearly increases in fluoroscopic procedures and improvements in pediatric patient long term outcome, the need for accurate quantification of patient dose emerged. Creation of the University of Florida/National Cancer Institute family of hybrid computational pediatric phantoms has made patient-dependent calculations feasible. To demonstrate the pediatric phantom libraries acceptability as a surrogate for patient-specific information a validation study was completed. A cohort of ten pediatric patients, five male and five female, were chosen to span age, height and weight. Computed tomography scans were acquired for each patient and segmentation was performed on eight internal organs to create patient-specific phantoms. The appropriate library phantom hybrid match was selected for each patient, based on height and weight. Next, radiation transport using Monte Carlo N-Particle was completed on both the patient-dependent and patient-specific phantoms to determine respective organ doses. A variation of realistic in-clinic parameters were included to simulate a representative cardiac fluoroscopy exam. These values were normalized to the kerma air product meter reading observed within the same radiation transport run.  Finally, in-field organs and out of field organs were determined, organ doses were acquired and compared between patient-specific and patient-dependent phantoms. Absolute relative error calculations were made to evaluate performance of the patient-dependent hybrid phantom as compared to the patient-specific phantom. The highest cumulative relative error for a hybrid phantom was seen when considering all organs, out of field inclusive, with the smallest field of view 0.81. The lowest cumulative relative error was seen in the medium field of view for a male patient 0.06. Trends for relative error performed as expected. Increasing field of view led to significant decreases in relative error values due to less partial organ irradiation. The higher energy, as expected, produced lower relative errors in comparison to the lower energy based on scatter properties. Overall the library phantoms performed extremely well in comparison to the patient-specific phantoms, maintaining an in-field organ relative error mean of 15-28% field of view dependent. This study shows promising preliminary results, the University of Florida/National Cancer Institute family of hybrid computational pediatric phantoms provide reasonably accurate models for in-clinic dosimetry studies.