Monte Carlo Study on Dose Distributions Around 192Ir, 169Yb, and 125I Brachytherapy Sources Using EGSnrc-based egs_brachy User-code.

Introduction: As per the recommendations of the American Association of Physicists in Medicine Task Group 43, Monte Carlo (MC) investigators should reproduce previously published dose distributions whenever new features of the code are explored. The purpose of the present study is to benchmark the TG-43 dosimetric parameters calculated using the new MC user-code egs_brachy of EGSnrc code system for three different radionuclides 192Ir, 169Yb, and 125I which represent high-, intermediate-, and low-energy sources, respectively. Materials and Methods: Brachytherapy sources investigated in this study are high-dose rate (HDR) 192Ir VariSource (Model VS2000), 169Yb HDR (Model 4140), and 125I -low-dose-rate (LDR) (Model OcuProsta). The TG-43 dosimetric parameters such as air-kerma strength, S k, dose rate constant, Λ, radial dose function, g(r) and anisotropy function, F(r,θ) and two-dimensional (2D) absorbed dose rate data (along-away table) are calculated in a cylindrical water phantom of mass density 0.998 g/cm3 using the MC code egs_brachy. Dimensions of phantom considered for 192Ir VS2000 and 169Yb sources are 80 cm diameter ×80 cm height, whereas for 125I OcuProsta source, 30 cm diameter ×30 cm height cylindrical water phantom is considered for MC calculations. Results: The dosimetric parameters calculated using egs_brachy are compared against the values published in the literature. The calculated values of dose rate constants from this study agree with the published values within statistical uncertainties for all investigated sources. Good agreement is found between the egs_brachy calculated radial dose functions, g(r), anisotropy functions, and 2D dose rate data with the published values (within 2%) for the same phantom dimensions. For 192Ir VS2000 source, difference of about 28% is observed in g(r) value at 18 cm from the source which is due to differences in the phantom dimensions. Conclusion: The study validates TG-43 dose parameters calculated using egs_brachy for 192Ir, 169Yb, and 125I brachytherapy sources with the values published in the literature.

EGSnrc-based depth-dependent photon energy response and phantom scatter corrections for low-energy brachytherapy sources.

In the present study, beam quality correction, [Formula: see text], and phantom scatter correction, kphan(r), for low-energy brachytherapy sources, 131Cs, 125I, and 103Pd, are calculated using the Monte Carlo-based EGSnrc code system as a function of the distance along the transverse axis of the source. The solid-state detectors investigated are diamond, LiF, Li2B4O7, Al2O3, and radiochromic films, such as HS, EBT, EBT2, EBT3, RTQA, XRT, and XRQA. The solid phantoms investigated are polystyrene, PMMA, virtual water, solid water, plastic water (LR), A150, RW1, RW3, and WE210. For a given detector and brachytherapy source, [Formula: see text] is independent of distance in the water phantom. Meanwhile, for a given detector, kphan(r) depends on the distance from the source for the investigated solid phantoms. Moreover, the kphan(r) values do not change with the detector type for sources 131Cs, 125I, and 103Pd at all distances. The LR and A150 phantoms are water equivalent for the investigated distances of 1-5 cm. The phantoms including solid water, virtual water, and WE210 are not water-equivalent for distances beyond 1 cm. Furthermore, PMMA, polystyrene, RW1, and RW3 are not water equivalent.

Comparison of Measured and Monte Carlo Calculated Dose Distributions from Indigenously Developed 6 MV Flattening Filter Free Medical Linear Accelerator.

PURPOSE: Monte Carlo simulation was carried out for a 6 MV flattening filter-free (FFF) indigenously developed linear accelerator (linac) using the BEAMnrc user-code of the EGSnrc code system. The model was benchmarked against the measurements. A Gaussian distributed electron beam of kinetic energy 6.2 MeV with full-width half maximum of 1 mm was used in this study. METHODS: The simulation of indigenously developed linac unit has been carried out by using the Monte Carlo-based BEAMnrc user-code of the EGSnrc code system. Using the simulated model, depth and lateral dose profiles were studied using the DOSXYZnrc user-code. The calculated dose data were compared against the measurements using an RFA dosimertic system made by PTW, Germany (water tank MP3-M and 0.125 cm3 ion chamber). RESULTS: The BEAMDP code was used to analyze photon fluence spectra, mean energy distribution, and electron contamination fluence spectra. Percentage depth dose (PDD) and beam profiles (along both X and Y directions) were calculated for the field sizes 5 cm × 5 cm - 25 cm × 25 cm. The dose difference between the calculated and measured PDD and profile values were under 1%, except for the penumbra region where the maximum deviation was found to be around 3%. CONCLUSIONS: A Monte Carlo model of indigenous FFF linac (6 MV) has been developed and benchmarked against the measured data.

Monte Carlo Investigation of Photon Beam Characteristics and its Variation with Incident Electron Beam Parameters for Indigenous Medical Linear Accelerator.

PURPOSE: A Monte Carlo model of a 6 MV medical linear accelerator (linac) unit built indigenously was developed using the BEAMnrc user code of the EGSnrc code system. The model was benchmarked against the measurements. Monte Carlo simulations were carried out for different incident electron beam parameters in the study. MATERIALS AND METHODS: Simulation of indigenously developed linac unit has been carried out using the Monte Carlo based BEAMnrc user-code of the EGSnrc code system. Using the model, percentage depth dose (PDD), and lateral dose profiles were studied using the DOSXYZnrc user code. To identify appropriate electron parameters, three different distributions of electron beam intensity were investigated. For each case, the kinetic energy of the incident electron was varied from 6 to 6.5 MeV (0.1 MeV increment). The calculated dose data were compared against the measurements using the PTW, Germany make RFA dosimetric system (water tank MP3-M and 0.125 cm3 ion chamber). RESULTS: The best fit of incident electron beam parameter was found for the combination of beam energy of 6.2 MeV and circular Gaussian distributed source in X and Y with FWHM of 1.0 mm. PDD and beam profiles (along both X and Y directions) were calculated for the field sizes from 5 cm × 5 cm to 25 cm × 25 cm. The dose difference between the calculated and measured PDD and profile values were under 1%, except for the penumbra region where the maximum deviation was found to be around 2%. CONCLUSIONS: A Monte Carlo model of indigenous linac (6 MV) has been developed and benchmarked against the measured data.