Analysis of a computational problem involving complex voxel geometries

Quality assurance for the use of computational methods in dosimetry: activities of EURADOS Working Group 6 'Computational Dosimetry'

Working Group (WG) 6 'Computational Dosimetry' of the European Radiation Dosimetry Group promotes good practice in the application of computational methods for radiation dosimetry in radiation protection and the medical use of ionising radiation. Its cross-sectional activities within the association cover a large range of current topics in radiation dosimetry, including more fundamental studies of radiation effects in complex systems. In addition, WG 6 also performs scientific research and development as well as knowledge transfer activities, such as training courses. Monte Carlo techniques, including the use of anthropomorphic and other numerical phantoms based on voxelised geometrical models, play a strong part in the activities pursued in WG 6. However, other aspects and techniques, such as neutron spectra unfolding, have an important role as well. A number of intercomparison exercises have been carried out in the past to provide information on the accuracy with which computational methods are applied and whether best practice is being followed. Within the exercises that are still ongoing, the focus has changed towards assessing the uncertainty that can be achieved with these computational methods. Furthermore, the future strategy of WG 6 also includes an extension of the scope toward experimental benchmark activities and evaluation of cross-sections and algorithms, with the vision of establishing a gold standard for Monte Carlo methods used in medical and radiobiological applications.

Monte Carlo simulation of in vivo measurement of the most suitable knee position for the optimal measurement of activity

A new computational model has been developed using the Monte Carlo (MC) technique to simulate in vivo measurements with the objective of understanding the most precise measurement location with respect to quantifying the activity of Am in the bones. To benchmark the model, in vivo measurements were performed on the U.S. Transuranium and Uranium Registries (USTUR) case 0846 leg. Front and lateral measurements of the knee of the USTUR case 0846 leg in a bent position and the same measurements with the leg in a straight position using a HP(Ge) detector were completed. Experimental results concluded that the front measurement of the knee in a bent leg position gave the highest count rate, which is an indication of optimal detection efficiency. Therefore, this geometry and knee-detector position were considered as the most appropriate position for knee monitoring. A computational model using MCNPX version 2.6.0 was used to simulate the experimental measurements by using a leg voxel phantom. The mean value and standard deviation (SD) of peak efficiency due to an isotropic 59.5-keV photon from Am were calculated in four different counting geometries. An extra sum of squares F-test was performed on the mean values of the simulated detection efficiencies. The p-value obtained from this statistical test indicates that the differences among the mean values for different counting geometries were significant. These results suggest that the front measurement of a knee in a bent leg position is the optimal counting geometry for in vivo measurement of Am deposited in the bones. The computational model was validated through comparison of the measured and simulated detection efficiencies. It was observed that there is no difference at the 0.1 significant levels between the simulated and measured detection efficiencies in assessment of Am within the bones.