Teste | Abstract: 46-1 | ||||
Abstract:Brachytherapy is an oncological treatment modality characterized by the application of radiation at a short distance [1]. This proximity between the radiation source and the target region is crucial for the efficacy of the treatment [1,2]. The precise positioning of the implant in brachytherapy is critical, as it directly influences the dosimetry of the radiation source [3]. The Task Group 43 (TG-43) of the American Association of Physicists in Medicine (AAPM) has developed guidelines for the dosimetry of interstitial brachytherapy, ensuring precision, safety, and effectiveness in the treatment of cancerous regions [4,5,6]. These guidelines provide essential recommendations and standardizations for clinical practice. The present study aims to investigate and validate, through Monte Carlo simulations, the influence of the radiation source geometry (point, linear, and volumetric) on the relative dose distribution as described by TG-43. The calculations were performed for the relative dose distribution such as: geometry and radial dose and anisotropy functions. The Monte Carlo codes MCNP6.2 and TOPAS 3.9 were used to model two brachytherapy sources: the Low Dose Rate (LDR) 125I (model Theragenic-AgX100) with half-lives of 60 days and average energy of 28 keV and the High Dose Rate (HDR) 192Ir (model MicroSelectron-HDR) with half-lives of 74.3 days and average energy of 380 keV. The targets consist of small water spheres of varying radii and distances relative to the source. The new feature provided by the MCNP6.2 code allows us to obtain the contribution of the different types of photon interactions within the irradiated sample. This was performed using an advanced tool called TAG score, which provides a detailed analysis of the physical parameters and allows us to better understand real scenarios. The results obtained for the radial dose function in both MC codes showed agreement between the values, with no significant variations. The differences calculated for the radial dose function using point, linear, and volumetric sources were averaged below 3 to 7% when compared to the same model published in the literature and the TG-43 protocol, respectively [4,5]. However, the results obtained for the anisotropy function and the volumetric source showed a smoother and more realistic behavior compared to the point source, with differences of up to 32%, highlighting the effects of attenuation and absorption associated with the brachytherapy seed geometry, reinforcing the accuracy of the simulations. These results were compared with literature data, showing minimal variation concerning the values reported in previous studies. The study confirms that the definition of brachytherapy sources has minimal influence on the radial dose function but significantly impacts the anisotropy function, as expected. The use of the MCNP6.2 and TOPAS 3.9 codes for the simulations proved effective in evaluating the dosimetric parameters, providing reliable data that corroborate what is published in the literature. These findings underscore the importance of considering source geometry in brachytherapy dosimetry to ensure the precision and efficacy of oncological treatment. Keywords: Brachytherapy, MCNP, Monte Carlo Simulation, TG-43, TOPAS |