Dose Distribution of 192Ir HDR Brachytherapy Source Measurement using Gafchromic® EBT3 Film Dosimeter and TLD-100H

This study aims to measure the radial dose function and anisotropy function F(r, θ) of high Dose Rate (HDR) 192Ir source in a fabricated water-equivalent phantom using Gafchromic® EBT3 film and TLD-100H and to compare the results obtained with the MCNP5 calculated values. The phantom was fabricated using Perspex PMMA material. For, the EBT3 films with a required dimension and TLD-100H chips were placed at r=1, 2, 3, 5, and 10 cm from the source. The F(r, θ) measurements were carried out at r=1, 2, 3, 5, and 10 cm with the angle range from 10° to 170°. The result of from EBT3 film and TLD-100H was in good agreement (2.10%±1.99). Compared to MCNP5, the differences are within 0.31% to 11.47% for EBT3 film and 0.08% to 10.58% for TLD-100H. For the F(r, θ), an average deviation with the MCNP5 calculation is 4.94%±2.7. For both and F(r, θ), the effects are prominent at r=10 cm. At this distance, the response of both Gafchromic® EBT3 film and TLD-100H shows less sensitivity as the dose followed the inverse square law. This work demonstrates that Gafchromic® EBT3 film dosimeter and TLD-100H are suitable dosimeters in 192Ir dosimetric measurements at a radial distance of ˂5 cm

Standardization and Validation of Brachytherapy Seeds’ Modelling Using GATE and GGEMS Monte Carlo Toolkits

This study aims to validate GATE and GGEMS simulation toolkits for brachytherapy applications and to provide accurate models for six commercial brachytherapy seeds, which will be freely available for research purposes. The AAPM TG-43 guidelines were used for the validation of two Low Dose Rate (LDR), three High Dose Rate (HDR), and one Pulsed Dose Rate (PDR) brachytherapy seeds. Each seed was represented as a 3D model and then simulated in GATE to produce one single Phase-Space (PHSP) per seed. To test the validity of the simulations’ outcome, referenced data (provided by the TG-43) was compared with GATE results. Next, validation of the GGEMS toolkit was achieved by comparing its outcome with the GATE MC simulations, incorporating clinical data. The simulation outcomes on the radial dose function (RDF), anisotropy function (AF), and dose rate constant (DRC) for the six commercial seeds were compared with TG-43 values. The statistical uncertainty was limited to 1% for RDF, to 6% (maximum) for AF, and to 2.7% (maximum) for the DRC. GGEMS provided a good agreement with GATE when compared in different situations: a) Homogeneous water sphere, b) heterogeneous CT phantom, and c) a realistic clinical case. In addition, GGEMS has the advantage of very fast simulations. For the clinical case, where TG-186 guidelines were considered, GATE required 1 h for the simulation while GGEMS needed 162 s to reach the same statistical uncertainty. This study produced accurate models and simulations of their emitted spectrum of commonly used commercial brachytherapy seeds which are freely available to the scientific community. Furthermore, GGEMS was validated as an MC GPU based tool for brachytherapy. More research is deemed necessary for the expansion of brachytherapy seed modeling.

A Monte Carlo investigation of the dose distribution for new I-125 Low Dose Rate brachytherapy source in water and in different media

Permanent and temporary implantation of I-125 brachytherapy sources has become an official method for the treatment of different cancers. In this technique, it is essential to determine dose distribution around the brachytherapy source to choose the optimal treatment plan. In this study, the dosimetric parameters for a new interstitial brachytherapy source I-125 (IrSeed-125) were calculated with GATE/GEANT4 Monte Carlo code. Dose rate constant, radial dose function and 2D anisotropy function were calculated inside a water phantom (based on the recommendations of TG-43U1 protocol), and inside several tissue phantoms around the IrSeed-125 capsule. Acquired results were compared with MCNP simulation and experimental data. The dose rate constant of IrSeed-125 in the water phantom was about 1.038 cGy·h−1U−1 that shows good consistency with the experimental data. The radial dose function at 0.5, 0.9, 1.8, 3 and 7 cm radial distances were obtained as 1.095, 1.019, 0.826, 0.605, and 0.188, respectively. The results of the IrSeed-125 is not only in good agreement with those calculated by other simulation with MCNP code but also are closer to the experimental results. Discrepancies in the estimation of dose around IrSeed-125 capsule in the muscle and fat tissue phantoms are greater than the breast and lung phantoms in comparison with the water phantom. Results show that GATE/GEANT4 Monte Carlo code produces accurate results for dosimetric parameters of the IrSeed-125 LDR brachytherapy source with choosing the appropriate physics list. There are some differences in the dose calculation in the tissue phantoms in comparison with water phantom, especially in long distances from the source center, which may cause errors in the estimation of dose around brachytherapy sources that are not taken account by the TG43-U1 formalism.

Determination of TG-43 dosimetric parameters for photon emitting brachytherapy sources

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.

Determination of dosimetric parameters for shielded 153Gd source in prostate cancer brachytherapy

Background Interstitial rotating shield brachytherapy (I-RSBT) is a recently developed method for treatment of prostate cancer. In the present study TG-43 dosimetric parameters of a 153Gd source were obtained for use in I-RSBT. Materials and methods A 153Gd source located inside a needle including a Pt shield and an aluminum window was simulated using MCNPX Monte Carlo code. Dosimetric parameters of this source model, including air kerma strength, dose rate constant, radial dose function and 2D anisotropy function, with and without the shields were calculated according to the TG-43 report. Results The air kerma strength was found to be 6.71 U for the non-shielded source with 1 GBq activity. This value was found to be 0.04 U and 6.19 U for the Pt shield and Al window cases, respectively. Dose rate constant for the non-shielded source was found to be 1.20 cGy/(hU). However, for a shielded source with Pt and aluminum window, dose rate constants were found to be 0.07 cGy/(hU) and 0.96 cGy/(hU), on the shielded and window sides, respectively. The values of radial dose function and anisotropy function were tabulated for these sources. Additionally, isodose curves were drawn for sources with and without shield, in order to evaluate the effect of shield on dose distribution. Conclusions Existence of the Pt shield may greatly reduce the dose to organs at risk and normal tissues which are located toward the shielded side. The calculated air kerma strength, dose rate constant, radial dose function and 2D anisotropy function data for the 153Gd source for the non-shielded and the shielded sources can be used in the treatment planning system (TPS).