TU-D-T-617-05: TG-43U1 Based Dosimetric Characterization of Model 67-6520 Cs-137 Brachytherapy Source

Abstract

Purpose: Dosimetric characteristics of a newly designed Cs-137 source (Model 67-6520) by Isotope Product Laboratories were determined using experimental and theoretical methods. These determinations were performed using TG-43U1 for distances larger than the active length of the source and along-away matrix for shorter distances. Method and Materials: Radial dose function, dose rate constant, 2D and 1D anisotropy function of the new Cs-137 source were determined following updated AAPM Task Group 43 (TG-43U1) recommendations. The experimental setup used for the determination of these parameters consisted of 1.0 × 1.0 × 1.0 mm3 and 3.2 × 3.2 × 0.89 mm3 TLD-100 LiF thermoluminescent dosimeters in Solid Water™ Phantom Material (40 × 40 × 20 cm3). TLD's were read using a Harshaw model 3500 TLD reader. The experimental results were compared to theoretical data using Monte Carlo simulations in liquid and Solid Water™. A Monte Carlo N-particle Transport Code (MCNP4C2) was used to calculate the dose rate distribution in Solid Water™ and liquid water. This code is capable of accounting for photoelectric, coherent, Compton and pair production interaction processes. The photon interaction cross section file used in this study was DLC-200 library distributed by the Radiation Shielding Information Computing Center (RSICC). In this study, up to 20×106 photons were used for each simulation. Calculations were set up in the same design format as the TLD experiments. Results: The calculated dose rate constant in liquid water and Solid Water™ were found to be 0.961 cGyh−1U−1 and 0.962 cGyh−1U−1, respectively. In addition, there was good agreement between the measured and calculated dose rate constant, radial dose function and the anisotropy function in Solid Water™. Conclusion: The dosimetric characteristics of the IPL 67-6520 Cs-137 source were determined using the TG-43U1 recommendation. The characteristics of the new Cs-137 source are comparable to the other commercially available sources.