Evaluation of skin absorbed doses during manipulation of radioactive sources: a comparison between the VARSKIN code and Monte Carlo simulations
The evaluation of skin doses during manipulation of radioactive sources can be a critical issue for which the most accurate calculation strategies available should be used. The aim of this work was to compare the results of the analytical approach used in VARSKIN with the simulation of radiation transport and interaction by Monte Carlo calculations in GAMOS (GEANT4-based Architecture for Medicine-Oriented Simulations), and to provide an accurate and versatile tool for the evaluation of skin doses from radionuclide sources of any realistic shape (e.g. cylindrical, parallelepiped), even in the presence of multiple interposed absorber layers. A set of 20 radionuclides (pure β, β–γ, Auger and γ emitters) from among the most frequently employed in nuclear medicine and laboratory practices were selected for comparison. We studied a point-like and a cylindrical source, in the presence of varying thicknesses of absorbing layers. We found a general agreement for most nuclides when the source was directly in contact with skin or in the presence of a thin layer of absorbing material. However, when the thickness of the absorber increased, significant differences were found for several nuclides. In these cases, the proposed method based on a dedicated Monte Carlo simulation could give more accurate results in a reasonable time, which could optimise accuracy when assessing skin doses in routine as well as incidental exposure scenarios.
Radiation protection from external exposure to radionuclides: A Monte Carlo data handbook.
The availability of a resource collecting dose factors for the evaluation of the absorbed doses from external exposure during the manipulation of radioactive substances is fundamental for radiological protection purposes. Monte Carlo simulations are useful for the accurate calculation of dose distributions in complex geometries, particularly in presence of extended spectra of multi-radiation sources. We considered, as possible irradiation scenarios, a point source, a uniform planar source resembling a contaminated surface, several source volumes contained in plastic or glass receptacles, and the direct skin contamination case, implementing the corresponding Monte Carlo simulations in GAMOS (GEANT4-based Architecture for Medicine-Oriented Simulations). A set of 50 radionuclides was studied, focusing the attention on those ones mainly used in nuclear medicine, both for diagnostic and therapeutic purposes, in nuclear physics laboratories and for instrument calibration. Skin dose equivalents at 70 μm of depth and deep dose equivalents at 10 mm of depth are reported for different configurations and organized in easy-to-read tables.
Absorbed fractions for electrons in ellipsoidal volumes
We applied a Monte Carlo simulation in Geant4 in order to calculate the absorbed fractions for monoenergetic electrons in the energy interval between 10 keV and 2 MeV, uniformly distributed in ellipsoids made from soft tissue. For each volume, we simulated a spherical shape, four oblate and four prolate ellipsoids, and one scalene shape. For each energy and for every geometrical configuration, an analytical relationship between the absorbed fraction and a ‘generalized radius’ was found, and the dependence of the fit parameters from electron energy is discussed and fitted by proper parametric functions. With the proposed formulation, the absorbed fraction for electrons in the 10–2000 keV energy range can be calculated for all volumes and for every ellipsoidal shape of practical interest. This method can be directly applied to evaluation of the absorbed fraction from the radionuclide emission of monoenergetic electrons, such as Auger or conversion electrons. The average deposited energy per disintegration in the case of extended beta spectra can be evaluated through integration. Two examples of application to a pure beta emitter such as 90Y and to 131I, whose emission include monoenergetic and beta electrons plus gamma photons, are presented. This approach represent a generalization of our previous studies, allowing a comprehensive treatment of absorbed fractions from electron and photon sources uniformly distributed in ellipsoidal volumes of any ellipticity and volume, in the whole range of practical interest for internal dosimetry in nuclear medicine applications, as well as in radiological protection estimations of doses from an internal contamination.