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
PurposeHDR 60Co system has recently been developed and utilized for brachytherapy in many countries outside of the U.S. as an alternative to 192Ir. In addition, the AccuBoost® technique has been demonstrated to be a successful non-invasive image-guided breast brachytherapy treatment option. The goal of this project is to evaluate the possibility of utilizing the BEBIG HDR 60Co system for AccuBoost treatment. These evaluations are performed with Monte Carlo (MC) simulation technique.Material and methodsIn this project, the MC calculated dose distributions from HDR 60Co for various breast sizes have been compared with the simulated data using an HDR 192Ir source. These calculations were performed using the MCNP5 code. The initial calculations were made with the same applicator dimensions as the ones used with the HDR 192Ir system (referred here after as standard applicator). The activity of the 60Co source was selected such that the dose at the center of the breast would be the same as the values from the 192Ir source. Then, the applicator wall-thickness for the HDR 60Co system was increased to diminish skin dose to levels received when using the HDR 192Ir system. With this geometry, dose values to the chest wall and the skin were evaluated. Finally, the impact of a conical attenuator with the modified applicator for the HDR 60Co system was analyzed.ResultsThese investigations demonstrated that loading the 60Co sources inside the thick-walled applicators created similar dose distributions to those of the 192Ir source in the standard applicators. However, dose to the chest wall and breast skin with 60Co source was reduced using the thick-walled applicators relative to the standard applicators. The applicators with conical attenuator reduced the skin dose for both source types.ConclusionsThe AccuBoost treatment can be performed with the 60Co source and thick-wall applicators instead of 192Ir with standard applicators.
The family members or friends of the patients undergoing treatment using radioiodine in nuclear medicine are inevitably exposed to ionization radiation. The purpose of this study is measurement of the dose received by the people taking care of the thyroid cancer patients treated by 131I. For this purpose, the dose amounts received by 29 people accompanying patients were measured using thermoluminescence dosimeters. A badge containing three TLD-100 chips was given to each caregiver. The people were asked to wear the badges for 24 days, when they are taking care of the patients. Finally the dose to each person was estimated by averaging the readings of the three TLDs. The measured dose amounts to the people were compared with the recommendations of international commitions. According to the results obtained in this study, the amounts of dose received by the caregivers were between 0.03 and 0.38 mSv, with the average of 0.12 mSv. By comparison of the results of this study with the recommendations of International Commission on Radiological Protection (ICRP), it can be observed that the dose to family members of the patients is less than the dose constraints. However, it is recommended that the caregivers be aware of the radiation protection principles in order to reduce their dose.
Currently, the use of blood irradiation for inactivating pathogenic microbes in infected blood products and preventing graft‐versus‐host disease (GVHD) in immune suppressed patients is greater than ever before. In these systems, dose distribution and uniformity are two important concepts that should be checked. In this study, dosimetry of the gamma chamber blood irradiator model Gammacell 3000 Elan was performed by several dosimeter methods including thermoluminescence dosimeters (TLD), PAGAT gel dosimetry, and Monte Carlo simulations using MCNP4C code. The gel dosimeter was put inside a glass phantom and the TL dosimeters were placed on its surface, and the phantom was then irradiated for 5 min and 27 sec. The dose values at each point inside the vials were obtained from the magnetic resonance imaging of the phantom. For Monte Carlo simulations, all components of the irradiator were simulated and the dose values in a fine cubical lattice were calculated using tally F6. This study shows that PAGAT gel dosimetry results are in close agreement with the results of TL dosimetry, Monte Carlo simulations, and the results given by the vendor, and the percentage difference between the different methods is less than 4% at different points inside the phantom. According to the results obtained in this study, PAGAT gel dosimetry is a reliable method for dosimetry of the blood irradiator. The major advantage of this kind of dosimetry is that it is capable of 3D dose calculation.PACS number: 87.53.Bn
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