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.
Dose to Medical Personnel.
Radioiodine I is successfully used in nuclear medicine for the treatment of hyperthyroidism and thyroid cancer. This radionuclide emits β particles used for the treatment and gamma photons used for diagnosis. The aim of this study is to determine gamma radiation doses received by medical personnel situated at a distance of 1 m from patients having ingested I for the treatment of hyperthyroidism diseases. Indeed, gamma doses were calculated using a Monte Carlo code based on simulating the interaction processes of gamma photons emitted by I in the thyroid gland, air, and an ambient flow meter placed at a distance of 1 m from the thyroid gland to measure the administered I activity. The thyroid volume of patients was measured by means of a gamma camera. Gamma dose equivalent rates were measured by means of an ambient flow meter situated at a distance of 1 m from the thyroid of the treated patients. Data obtained by the Monte Carlo and experimental methods were found to be in good agreement with each other.
Optimization of a monolithic detector block design for a prototype human brain PET scanner
We are presently developing a novel PET scanner for human brain functional imaging based on monolithic scintillator crystals read by APD matrices, capable of being inserted into an MRI system. In this work we report on the detailed study that has been made of the design of the detector blocks, aiming at defining the most suitable geometrical and readout configuration for optimizing the overall performance of the entire scanner. Both parallel and trapezoidal geometries have been simulated, featuring two layers of active scintillator material with different or similar thickness and APD readout on the front or back side. Results of this study indicate that a trapezoidal geometry with equal thickness of both layers is the best solution for improving the expected scanner performance.