Collapsed cone convolution and analytical anisotropic algorithm dose calculations compared to VMC++ Monte Carlo simulations in clinical cases

The purpose of this work was to study and quantify the differences in dose distributions computed with some of the newest dose calculation algorithms available in commercial planning systems. The study was done for clinical cases originally calculated with pencil beam convolution (PBC) where large density inhomogeneities were present. Three other dose algorithms were used: a pencil beam like algorithm, the anisotropic analytic algorithm (AAA), a convolution superposition algorithm, collapsed cone convolution (CCC), and a Monte Carlo program, voxel Monte Carlo (VMC++). The dose calculation algorithms were compared under static field irradiations at 6 MV and 15 MV using multileaf collimators and hard wedges where necessary. Five clinical cases were studied: three lung and two breast cases. We found that, in terms of accuracy, the CCC algorithm performed better overall than AAA compared to VMC++, but AAA remains an attractive option for routine use in the clinic due to its short computation times. Dose differences between the different algorithms and VMC++ for the median value of the planning target volume (PTV) were typically 0.4% (range: 0.0 to 1.4%) in the lung and -1.3% (range: -2.1 to -0.6%) in the breast for the few cases we analysed. As expected, PTV coverage and dose homogeneity turned out to be more critical in the lung than in the breast cases with respect to the accuracy of the dose calculation. This was observed in the dose volume histograms obtained from the Monte Carlo simulations.

High-resolution computer simulations of EKC

The electrophoresis simulation software, GENTRANS, has been modified to include the interaction of analytes with an electrolyte additive to allow the simulation of liquid-phase EKC separations. The modifications account for interaction of weak and strong acid and base analytes with a single weak or strong acid or base background electrolyte additive and can be used to simulate a range of EKC separations with both charged and neutral additives. Simulations of separations of alkylphenyl ketones under real experimental conditions were performed using mobility and interaction constant data obtained from the literature and agreed well with experimental separations. Migration times in fused-silica capillaries and linear polyacrylamide-coated capillaries were within 7% of the experimental values, while peak widths were always narrower than the experimental values, but were still within 50% of those obtained by experiment. Simulations of sweeping were also performed; although migration time agreement was not as good as for simple EKC separations, peak widths were in good agreement, being within 1-50% of the experimental values. All simulations for comparison with experimental data were performed under real experimental conditions using a 47 cm capillary and a voltage of 20 kV and represent the first quantitative attempt at simulating EKC separations with and without sweeping.