Canine Anatomic Phantom for Preclinical Dosimetry in Internal Emitter Therapy

Abstract

The majority of investigational studies of new diagnostic and therapeutic radiopharmaceuticals use murine animal models for preclinical assessments of pharmacokinetics and organ radiation dosimetry. Although mice and rats are widely available and relatively inexpensive, their smaller organ anatomy relative to that of humans can lead to considerable differences in organ dosimetry, thus complicating extrapolations of dose-response relationships to human patients. Nonhuman primates circumvent these problems in many respects but are increasingly becoming expensive and limited because of ethical considerations. With the recent completion of the dog genome project and the recognition of many similarities between canine and human cancers, dogs are increasingly being considered in cancer research and drug development. The main objective of this study was to construct a 3-dimensional computational phantom of a large dog on the basis of whole-body multislice CT data. Methods: A female hound cross underwent whole-body contrast-enhanced CT at a 2-mm slice thickness. On completion of the scan, the dog was euthanized, and the entire skeleton was harvested for a subsequent microCT investigation. The CT data were imported into a computational software program and used to create a polygon-mesh phantom of the entire animal. All of the major organs and bones were semiautomatically segmented and tagged to the CT slices. The phantom data were imported into a second software program and transformed to a nonuniform rational basis-spline surface phantom, allowing easy alteration of the phantom to simulate dogs of smaller or larger statures. A voxel-based version of the canine phantom was created by use of an in-house routine for subsequent import into the EGSnrc radiation transport code for photon and b-particle organ dosimetry. Results: The resulting voxel-based version of the canine phantom had a total body mass of 26.0 kg and a total body tissue mass (exclusive of wall organ content) of 24.5 kg. Although this University of Florida (UF) canine phantom displayed a total body mass intermediate between those of the Oak Ridge National Laboratory (ORNL) 5-y and 10-y stylized human phantoms of the MIRDOSE and OLINDA software codes, considerable differences were noted in organ photon cross-doses. For example, ratios of the specific absorbed fraction F(lungs ) liver) UF Dog to F(lungs ) liver) ORNL 5-y ranged from ;30 at 10 keV to ;3.5 at 1 MeV. Corresponding ratios of F(lungs ) liver) UF Dog to F(lungs ) liver) ORNL 10-y ranged from ;6 at 10 keV to ;1.3 at 1 MeV. Conversely, values of F(kidneys ) spleen) and F(liver ) spleen) were noted to be much lower (factors of 2-4) and much higher (factors of 2-15), respectively, in the canine phantom than in the ORNL human phantoms. These differences were attributed more to organ shape and position within the torso than to organ mass, because many of the canine organs closely approximated their counterparts volumetrically in the stylized pediatric human phantoms. Conclusion: The use of canine models, ...

Voxel modeling of rabbits for use in radiological dose rate calculations

“…Voxel models completed to date and utilized in an environmental context include a crab, flatfish, trout, rat, mouse, and frog (Caffrey and Higley, 2013;Caffrey, 2012;Ruedig et al, 2014b;Stabin et al, 2006;Kinase, 2008). Additional voxel models available to interested researchers include, but are not limited to, Digimouse, and two different canine models (Dogdas et al, 2007;Padilla et al, 2008;Kramer et al, 2012). Additionally, there are two "compromise" options between the basic single ellipsoid models and voxel models that are worth mentioning.…”

Feasibility study of a new platform based on the Case-Based Reasoning principles to efficiently search and store voxel phantoms

“…ADELAIDE (Caon et al, 1999), GOLEM (Zankl et al, 2001), developed by Zankl and Wittmann are also voxel phantoms, same for FAX (Kramer et al, 2003) and MAX (Kramer et al, 2004) that were made to fit the ICRP Publication 89 (ICRP, 2002) recommendations regarding organs weights. VIP-Man created by Xu (Xu et al, 2000) and the Canine Anatomic Phantom designed by Padilla (Padilla et al, 2008). More details about the characteristics and availability of voxel phantoms can be found on the reviews by Lemosquet and Zaidi (Lemosquet et al, 2003;Zaidi and Xu, 2007).…”

Development of computational small animal models and their applications in preclinical imaging and therapy research

“…Figure 8 shows representative models of the stylized deer model of ICRP, 38 a voxel trout model, 50 and a hybrid canine model. 53 The body of the adult reference deer is roughly represented by an ellipsoid with dimensions of 50,52,65 A voxel-based frog model was also developed using cryosection images. 51 Toivonen et al 54 and Wake et al, 55 developed voxelbased pig and rabbit models, respectively, for finite-difference time-domain (FDTD) simulation of radio frequency (RF) radiation dosimetry.…”

“…Databases of AFs and S-values for animals, such as mouse, rat, frog, and canine, of monoenergetic photons and electrons and common radionuclides including F-18, P-32, Cu-64, Y-90, In-111, I-124, I-131, Sm-153, Pm-149, Ho-166, Lu-177, and Re-188, have been reported by various groups. 11,15,17,18,21,24,27,33,39,45,46,49,53,[78][79][80][81][82] These were largely adopted for calculation of organ absorbed dose and dosimetry of radionuclide-labeled compounds in preclinical experiments. [83][84][85][86][87][88][89][90][91][92][93][94][95] These computational models were also integrated in comparative Monte Carlo-based simulations studies investigating patterns of uptake and biodistribution data of radiopharmaceuticals for the purpose of dose estimation in molecular radiotherapy and diagnostic nuclear medical imaging procedures.…”