ABSTRACT
This study primarily aimed to obtain the dosimetric characteristics of the Model 6733 (125)I seed (EchoSeed) with improved precision and accuracy using a more up-to-date Monte-Carlo code and data (MCNP5) compared to previously published results, including an uncertainty analysis. Its secondary aim was to compare the results obtained using the MCNP5, MCNP4c2, and PTRAN codes for simulation of this low-energy photon-emitting source. The EchoSeed geometry and chemical compositions together with a published (125)I spectrum were used to perform dosimetric characterization of this source as per the updated AAPM TG-43 protocol. These simulations were performed in liquid water material in order to obtain the clinically applicable dosimetric parameters for this source model. Dose rate constants in liquid water, derived from MCNP4c2 and MCNP5 simulations, were found to be 0.993 cGyh(-1) U(-1) (±1.73%) and 0.965 cGyh(-1) U(-1) (±1.68%), respectively. Overall, the MCNP5 derived radial dose and 2D anisotropy functions results were generally closer to the measured data (within ±4%) than MCNP4c and the published data for PTRAN code (Version 7.43), while the opposite was seen for dose rate constant. The generally improved MCNP5 Monte Carlo simulation may be attributed to a more recent and accurate cross-section library. However, some of the data points in the results obtained from the above-mentioned Monte Carlo codes showed no statistically significant differences. Derived dosimetric characteristics in liquid water are provided for clinical applications of this source model.
Subject(s)
Brachytherapy/instrumentation , Brachytherapy/methods , Iodine Radioisotopes/pharmacology , Radiometry/methods , Algorithms , Anisotropy , Computer Simulation , Equipment Design , Humans , Monte Carlo Method , Photons , Radiotherapy Dosage , Reproducibility of ResultsABSTRACT
PURPOSE: In this project, the Patterson-Parker Table has been updated for Cs-137 and Ir-192 sources using their recent TG-43U1 dosimetric data. In addition, dose uniformity for the different loading schemes as a function of implant area has been verified. METHODS: The updated Paterson-Parker tables have been generated for planar implants with Cs-137 and Ir-192 sources using their published TG-43U1 dosimetric parameters. Accuracies of the updated tables were examined by two independent methods, namely, Monte Carlo simulation technique and using a commercially available treatment planning system. In addition to the dose values along the central axis of the implant, dose profiles along two orthogonal directions have been evaluated for selection of the optimum radioactivity distribution in each implant geometry. RESULTS: The results of these investigations show that for the same implant size the mg.hr required for delivery of a given dose with Cs-137 is not identical to that of Ir-192. In addition, some differences between the updated Table and the published Paterson-Parkers Tables have been observed. Independent Monte Carlo simulations and treatment planning data for multi-seed implant indicated the accuracy (less than ±5%) of the updated Table. CONCLUSIONS: This work gives complete updated Paterson-Parker Tables for two of the commonly utilized brachytherapy sources. For delivery of a given dose, significant differences (approximately 35%) have been observed between the traditional Paterson-Parker Table and the updated Tables. These differences are attributed to the differences of tissue attenuation, 2D anisotropy functions as well as the availability of the new source dosimetry.
