Objective: Brachytherapy sources are widely used for the treatment of cancer. The report of Task Group No. 43 (TG-43) of American Association of Physicists in Medicine is known as the most common method for the determination of dosimetric parameters for brachytherapy sources. The aim of this study is to obtain TG-43 dosimetric parameters for 60Co, 137Cs, 192Ir and 103Pd brachytherapy sources by Monte Carlo simulation. Methods: In this study, 60Co (model Co0. A86), 137Cs (model 6520-67), 192Ir (model BEBIG) and 103Pd (model OptiSeed) brachytherapy sources were simulated using MCNPX Monte Carlo code. To simulate the sources, the exact geometric characterization of each source was defined in Monte Carlo input programs. Dosimetric parameters including air kerma strength, dose rate constant, radial dose function and anisotropy function were calculated for each source. Each input program was run with sufficient number of particle histories. The maximum type A statistical uncertainty in the simulation of the 60Co, 137Cs, 192Ir and 103Pd sources, were equal to 4%, 4%, 3. 19% and 6. 50%, respectively. Results: The results for dosimetry parameters of dose rate constant, radial dose function and anisotropy function for the 60Co, 137Cs, 192Ir and 103Pd sources in this study demonstrated good agreement with other studies. Conclusion: Based on the good agreement between the results of this study and other studies, the TG-43 results for Co0. A86 60Co, 67-65200 137Cs, BEBIG 192Ir and OptiSeed 103Pd sources are validated and can be used as input data in treatment planning systems (TPSs) and to validate the TPS calculations.

Background: Monte Carlo determination of TG-43 brachytherapy dosimetry parameters and dose distribution calculation for 131CSsource model CS-1 are presented in this study. Materials and Methods: The dose distribution was calculated around the 131CS Model CS-1 located in the center of 30 cm x30 cm x30 cm water, and soft tissue phantoms cube using MCNP code by Monte Carlo method. The percentage depth dose (POD) variation along the different axis, parallel and perpendicular, the source was calculated. Then, the isodose curves for 100%, 75%, 50% and 25% POD were constructed. Finally, F(r,q) and g(r) dosimetry parameters of TG-43 protocol have been determined. Results: Results obtained show that the Monte Carlo method could only calculate dose deposition in high gradient region, near the source, accurately. The energy cut off was found to be 1 eV and the error in the calculations was less than 2%. Conclusion: The isodose curves of the CS-1 131CS source were constructed from dose calculation by MCNPcode. The calculated dosimetry parameters for the source were in agreement with previously published results.

BACKGROUND: 125I is one of the important sources frequently used in brachytherapy. Up to now, several different commercial models of this source type have been introduced to the clinical radiation oncology applications. Recently, a new source model, IrSeed-125, has been added to this list. The aim of the present study is to determine the dosimetric parameters of this new source model based on the recommendations of TG-43 (U1) protocol using Monte Carlo simulation.METHODS: The dosimetric characteristics of Ir-125 including dose rate constant, radial dose function, 2D anisotropy function and 1D anisotropy function were determined inside liquid water using MCNPX code and compared to those of other commercially available iodine sources.RESULTS: The dose rate constant of this new source was found to be 0.983+0.015 cGyh-1U-1 that was in good agreement with the TLD measured data (0.965 cGyh-1U-1). The 1D anisotropy function at 3, 5, and 7 cm radial distances were obtained as 0.954, 0.953 and 0.959, respectively.CONCLUISON: The results of this study showed that the dosimetric characteristics of this new brachytherapy source are comparable with those of other commercially available sources. Furthermore, the simulated parameters were in accordance with the previously measured ones. Therefore, the Monte Carlo calculated dosimetric parameters could be employed to obtain the dose distribution around this new brachytherapy source based on TG-43 (U1) protocol.

It is important to have accurate information regarding the dose distribution for treatment planning and to accurately deposit that dose in the tissue surrounding the brachytherapy source. However, the practical measurement of dose distribution for various reasons is associated with several problems. In this study, 6711 I-125, Micro Selectron mHDR-v2r Ir-192, and Flexisource Co-60 sources were simulated using the MCNP5 Monte Carlo method. To simulate the sources, the exact geometric characteristics of each source, the material used in them, and the energy spectrum of each source were entered as input to the program, and finally, the dosimetric parameters including dose rate constant, radial dose function, and anisotropy function were calculated for considered seeds according to AAPM, TG-43 protocol recommendation. Results obtained for dosimetric parameters of dose rate constant, radial dose function, and anisotropy function for I-125, Ir-192, and Co-60 sources agreed with other studies. According to the good agreement obtained between the parameters of TG43 and other studies, now these datasets can be used as input in the treatment planning systems and to validate their calculations.

Background: The dose rate distribution delivered by a low dose rate 137Cs pellet source, a spherical source used within the source trains of the Selectron gynecological brachytherapy system, was investigated using the MCNP4C Monte Carlo code.Materials and Methods: The calculations were performed in both water and Plexiglas and the absolute dose rate distribution for a single pellet source and the AAPM TG-43 parameters were computed. A spherical phantom with dimensions large enough (60 cm) was used to provide full scattering conditions. In order to score dose at different distances from the source centre, this sphere was divided into a set of 600 concentric spherical shells of 0.05 cm thickness. The calculations were performed up to a distance of 10 cm from the source centre. To calculate the effect of the applicator and dummy pellets on dose rate constant and radial dose function, a single pellet source was simulated inside the vaginal applicator, and spherical tally cells with radius of 0.05 cm were used in the simulations. The F6 tally was used to score the absolute dose rate at a given point in the phantom. Results: The dose rate constant for a single active pellet was found to be 1.102±0.007 cGyh-1U-1, and the dose rate constant for an active pellet inside the applicator was 1.095±0.009 cGyh-1U-1. The tabulated data and 5th order polynomial fit coefficients for the radial dose function along with the dose rate constant are provided for both cases. The effect of applicator and dummy pellets on anisotropy function of the source was also investigated.Conclusion: The error resulting from ignoring the applicator was reduced using the data of a single pellet. The results indicate that F(r, q) decreases towards the applicator.  

Background: Iodine brachytherapy sources with low photon energies have been widely used in treating cancerous tumors. Dosimetric parameters of brachytherapy sources should be determined according to AAPM TG-43U1 recommendations before clinical use. Monte Carlo codes are reliable tools in calculation of these parameters for brachytherapy sources. Materials and Methods: Dosimetric parameters (dose rate constant, radial dose function, and anisotropy function) of two I-125 brachytherapy sources (models LS-1 and Intersource) were calculated with MCNP4C Monte Carlo code following task group #43 (TG-43U1) recommendations of American Assossiation of Physicists in Medicine. The simulations were done inside a spherical water phantom because of its tissue equivalent properties. The Monte Carlo simulations for radial dose function were performed at distances ranging from 0.25 to 10 cm from the source center. The anisotropy functions F(r, q), for both sources, were calculated at distances of 1, 2, 3, 5 and 7 cm from the source center for angles ranging from 15 to 90 degree. Results: The results of the Monte Carlo simulation indicated a dose rate constant of 0.952 cGyh -1U-1 and 0.986 cGyh -1U-1 for models LS-1 and Intersource, respectively. The tabulated data and fifth order polynomial coefficients for radial dose functions along the source are described in this paper .The results indicated that the anisotropy in dose distribution increased along the source axis. Conclusion: The obtained results were in good agreement with measurements and calculations of other investigators, using other Monte Carlo codes.