An Effective Hybrid Approach for Rapid Radiation Dose Assessments for Complex Source/Receptor Geometries, 20-R9570

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Principal Investigators
Oleg Povetko
Roland Benke
Consultants
Vladislav Golikov
(Federal Radiological Center, Institute of Radiation Hygiene,
Ministry of Health of the Russian Federation, St. Petersburg, Russia)
Alexei Kouznetsov

Inclusive Dates:  10/01/05 – 09/30/06

Background - Currently, there are no known rapid radiation dose assessment approaches that are computationally fast, sufficiently accurate, and easy to use for arbitrary three-dimensional geometries representing the radiation source and dose receptor. Commonly used radiation dose assessment methods are either deterministic or stochastic (e.g., Monte Carlo simulations). Deterministic methods can produce fairly complete information but for only a very narrow class of problems with simple source/receptor geometries. Stochastic methods, though highly accurate, are computationally demanding and time consuming, because during transport, particle interactions must be simulated sequentially. Clearly, both methods have practical limitations that restrict their use for rapid dose assessments. The purpose of this study is to develop (i) a hybrid approach that combines the advantages of both commonly used methods and (ii) a user-friendly interface that will allow this method to be widely used in health physics, environmental, medical, and educational applications. If successful, this project will result in a computational method faster than pure stochastic methods and more accurate than deterministic methods for a wide class of applications.

Approach - The proposed approach utilizes recent advances in three-dimensional object representation methods and some novel approximations in geometrical and physical models to compute radiation absorption. The method uses a novel chord distribution approach to accelerate the computation of dose inside the receptor body for radiation sources of complex geometries. Several generations of emitted, scattered, and newly born particles are modeled to create secondary sources. The method then uses stochastic simulation on the chord distribution using photon interaction data from the ENDF/B-VI library to compute absorbed radiation dose.

Accomplishments - A new computational framework, DosesFW, has been developed on the Microsoft® Visual Studio® platform. The framework prototype software consists of two major modules: geometrical and physical. The user-friendly framework interface presented in Figure 1 allows a user to create or import various elemental three-dimensional objects created by external graphic editors (in CAD, VRML, DXF, and other formats) on the "palette" (right screen), fill them with any composition of elements available in the ENDF/B-VI library, and transfer them into the "stage" (left screen) to build compound receptors of complex geometries. The radiation sources are entered as separate three-dimensional elements in a similar manner. The user may specify source characteristics by either arbitrary space-energy-angular distributions or by the concentrations of isotopes. Any isotope from the International Commission on Radiological Protection Report 38 may be specified just by its symbol. Then, the average absorbed dose for the complex object on the "stage" is calculated. The numerical dose values calculated by the framework agree well with the results calculated by the industry-standard MCNP5 code and with the literature data where three different stochastic codes were used for receptors of simple geometries irradiated by internal and external photon sources emitting photons of energies ranging between 20 Kev and 10 Mev. The agreement with MCNP5 results is within 1 percent. Work on implementing dose calculations for multilevel hierarchy of three-dimensional elements modeling actual human phantom geometry is currently underway.

Figure 1. DoseFW Prototype Software Interface. Three-dimensional element shown on palette (on the right) was transferred inside the cone (on the left) as an example of a compound receptor object with the hierarchy of composing elements. The three-dimensional elements are composed of elemental tetrahedrons (not shown inside of elements or the object).

©2006. Southwest Research Institute.

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