[Show abstract][Hide abstract]ABSTRACT: A routine dose computation around brachytherapy seeds employing the Fast Fourier Transform (FFT) has been demonstrated and likened to dose computations in a similar field based on the TG43 recommendations. In applying the FFT convolution model to dose computation, a dose convolution kernel which takes into consideration the anisotropy of the dose distribution around a brachytherapy source in the presence of tissue and applicator heterogeneities was presented. Resulting from the convolution kernel were functions with polynomial and exponential terms. The solution to the convolution integral was thus represented by the Fast Fourier transform. The versatility of the Fast Fourier Transform becomes evident with its speed of dose computation and accuracy evenly matched. It has also been described as ubiquitous; as successful procedures developed in one field could easily be adopted in other fields (E.g. external beam and brachytherapy). In typical dose computation procedures, the dose computation time is usually proportional to the number of sources or dwell positions required for the implants and relatively increases for large number of sources. With a dose convolution kernel developed for a 64x64x64 matrix size with wrap around ordering, the kernel was convoluted with the source distributions also in similar matrix size in 3D. Results from the analysis showed the FFT based convolution method in brachytherapy was comparable in speed with computerized treatment planning system whose model is based on the recommendations of the TG43. Further development on the FFT incorporating techniques such as the Monte Carlo simulation will be required to fine tune the potency of the FFT convolution in studying tumor growth and the aftermath upshots of radiation therapy.
[Show abstract][Hide abstract]ABSTRACT: A robust model to directly represent output from contemporary brachytherapy calculation had been proposed and developed to make clinical implementation practicable. The model was used to minimize inherent uncertainties associated with the AAMP TG-43 formalism, with consolidation of the TG-43 parameters into new parameter to speed up computational time. Analytical computations were performed to hybridize the anisotropy function, F(r,theta) and radial dose function, g(r,theta) into a single new function f(r,theta) for a Nucletron microSelectron High Dose Rate “new or v2” (mHDRv2) 192Ir brachytherapy source. Outputs obtained with the new function were curve fitted with MatLab and compared to those of Monte Carlo serving as the standard to evaluate the average and maximum uncertainties. Dose rate deviations between the Monte Carlo data and MatLab fits, quantified as errors showed minimal deviations less than 0.3%. In comparison with Lliso’s study, this work shows marginal improvement in the deviated values. This work has shown much promise in building robust models to represent outputs from contemporary brachytherapy dosimetry calculations.
[Show abstract][Hide abstract]ABSTRACT: Maximum count rate, accuracy, precision, constancy and linearity measurement have been undertaken on two dose calibrators at the Nuclear medicine department, Korle-Bu Teaching Hospital as part of quality control test. Both calibrators show some dependence on measurement geometry which deminishes with increasing depth in the well. It was observed that the measured activities for Co-57, Cs-137 and Tc-99m, obtained from the VDR-15R were larger than those from the reference dose calibrator, Capintec CRC-25R. It was found that, the maximum depth of sensitivity in the Capintec was 6.8 cm and 5.6 cm for Co-57 and Cs-137.VDR showed a maximum sensitivity depth of 5.2 cm for both Co-57 and Cs-137. For accuracy and precision, it was observed that, the percentage differences for the reference dose calibrator, Capintec CRC-25R was a little different from that of the VDR-15 but both calibrators were in the range of ±5% of the mean measured activity. The main difference was their maximum height of sensitivities with values of 6.8 cm and 5.2 cm for Co-57 and 5.6 cm and 5.2 cm for Cs-137 for Capintec and VDR-15R respectively. From the linearity test, there were systematic departures of the data points from the fitted straight line in the upper part and lower part and such discrepancies indicated non-linearity. These discrepancies in the upper and lower part were due to impurities (Mo-99 contaminants and Tc-99 contaminants respectively) in the Tc-99m used in the test which revealed itself in apparent levelling out of the activity in the final part and beginning part of the graph. Since most of the points fitted in the straight line, it showed that, almost all the individual activities measured in the test were within the range of ±10% of the values corresponding to the straight line fitted in the data points. It was observed that, the measured activities difference for both calibrators were very small which was as a result of the differences in depth of their wells. The dose calibrators can be used for dose measurements.