Hybrid Computational Phantom Of The Labrador With A Detailed Skeletal Model For Radiopharmaceutical Therapy Dosimetry

Date(s) - 05/20/2014
10:00 am

Michelle Sands, MS Medical Physics student

Survival rates for pediatric osteosarcoma have not shown any meaningful improvement since the introduction of chemotherapy in the 1970s. With the motivation of increasing the survival rates for these patients, an interdisciplinary research group here at the University of Florida seeks to develop a new polymer-based radiopharmaceutical for targeting radionuclide therapy of osteosarcoma. This research group includes areas of study such as biomedical engineering, medical physics, pediatric oncology, veterinary sciences, chemistry, and materials engineering. The basic principle upon which this radiopharmaceutical is being developed is the enhanced permeability and retention effect, which will selectively enter the tumor through its leaky vasculature. Client owned canines will be used in preclinical study of this radiopharmaceutical treatment due to their genetic and phenotypic similarities to humans. For this reason, a canine computational phantom becomes necessary to properly estimate organ absorbed doses to the enrolled canine patients. To represent the larger canine population, a canine computational phantom was created in the form of a three-dimensional NURBS/polygon mesh model based on a whole body CT of a 1.5-year-old labrador. To obtain macroscopic skeletal detail, the bones of the specimen were harvested and ex vivo CT images were acquired for each skeletal site. Segmentation of these skeletal sites was completed to find the cortical bone and the spongiosa volume fractions for each bone site. Next, to obtain skeletal microstructure detail, cored samples of spongiosa were further imaged under microCT at 30 micron resolution. The trabecular bone and marrow volume fractions were then calculated for each spongiosa core.  Additionally, marrow cellularity ranging from 10% to 100% was applied to each skeletal site image set. Finally, radiation transport was conducted using the MCNPX code for monoenergetic electrons ranging from 1 keV to 10 MeV within the macrostructure of each bone site.  Electron source regions included both cortical bone and spongiosa, with the target being spongiosa in each case.  A total of 25 bone sites were included in this dosimetry study.  The electron absorbed fractions obtained in the skeletal model of the Labrador followed trends seen in a recent study of the adult female skeleton.