Impact of the vaginal applicator and dummy pellets on the dosimetry parameters of Cs‐137 brachytherapy source

Abstract

In this study, dose rate distribution around a spherical 137Cs pellet source, from a low‐dose‐rate (LDR) Selectron remote afterloading system used in gynecological brachytherapy, has been determined using experimental and Monte Carlo simulation techniques. Monte Carlo simulations were performed using MCNP4C code, for a single pellet source in water medium and Plexiglas, and measurements were performed in Plexiglas phantom material using LiF TLD chips. Absolute dose rate distribution and the dosimetric parameters, such as dose rate constant, radial dose functions, and anisotropy functions, were obtained for a single pellet source. In order to investigate the effect of the applicator and surrounding pellets on dosimetric parameters of the source, the simulations were repeated for six different arrangements with a single active source and five non‐active pellets inside central metallic tubing of a vaginal cylindrical applicator. In commercial treatment planning systems (TPS), the attenuation effects of the applicator and inactive spacers on total dose are neglected. The results indicate that this effect could lead to overestimation of the calculated F(r,θ), by up to 7% along the longitudinal axis of the applicator, especially beyond the applicator tip. According to the results obtained in this study, in a real situation in treatment of patients using cylindrical vaginal applicator and using several active pellets, there will be a large discrepancy between the result of superposition and Monte Carlo simulations.PACS number: 87.53.Jw

Physics: Low-Energy Brachytherapy Physics

“…Cesium sources were widely used in low-dose gynecological implants such as cylinder, tandem, and ovoid implants. Cs-137 sources are used in low-dose afterloading devices [10].…”

Dosimetry of gamma chamber blood irradiator using PAGAT gel dosimeter and Monte Carlo simulations

“…Pelszynski et al (8,9) reported that the minimum possible radiation dose of only 25 Gy is necessary for lymphocytes to be efficiently inactivated in red blood cell units. Also, Anderson et al (10,11) mentioned that gamma irradiation is the only process that effectively prevents transfusion associated GVHD and suggested that blood components and products be irradiated to the lowest recommended dose (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) Gy) capable of preventing lymphocyte proliferation before blood transfusions. Nuclear radioactive sources like Cs-137 are used to deliver doses to blood products, and errors in calculating the radioactive decay of the radiation source (7) should be considered as a physical factor influencing the dose delivered to the blood product.…”

Dose distribution verification for GYN brachytherapy using EBT Gafchromic film and TG-43 calculation

“…11 In addition, this system contains some non-active pellets as a dummy, with the same dimensions and chemical composition as the active pellets. 6 Liu et al have published the TG-43 recommended dosimetric characteristics of the sources in this system. 12 In this study, from a set of 8 pellets, numbers 2-7 are considered active, and the remainders are non-active, in order to deliver 1.5 Gy of dose to 0.5 cm distance from the lateral surface of ovoids within 1.01 h.…”