Abstract:Medical linear accelerators, besides the clinically high energy electron and photon beams, produce other secondary particles such as neutrons which escalate the delivered dose. In this study the neutron dose at 10 and 18MV Elekta linac was obtained by using TLD600 and TLD700 as well as Monte Carlo simulation. For neutron dose assessment in 2020 cm2 field, TLDs were calibrated at first. Gamma calibration was performed with 10 and 18 MV linac and neutron calibration was done with 241Am-Be neutron source. For sim… Show more
“…Al respecto, Barquero y colaboradores midieron con pares de TLD la fluencia de neutrones térmicos en el cabezal de un acelerador lineal de 18 MV, en donde también obtuvieron fluencia y dosis equivalente por neutrones térmicos en la mesa de tratamiento [13]. Similarmente en otras investigaciones se han calculado también dosis equivalente por neutrones posicionando pares de TLD en un fantoma de calibración [14][15][16][17].…”
Mediante detectores de trazas tipo CR-39 se determinó la dosis equivalente ambiental H*(10) por neutrones rápidos y térmicos en un acelerador Varian Clinac 2300 que opera en el rango de 6-18 MV. Mediciones preliminares fueron efectuadas ante una fuente moderada de neutrones 252Cf para obtener la respuesta del detector según el rango de energía. Se obtuvieron valores de tasa de densidad de trazas, flujo y dosis equivalente ambiental H*(10) por neutrones rápidos y térmicos en la mesa de tratamiento del recinto. Se determinó que la dosis equivalente ambiental H*(10) por unidad de dosis Gy en el isocentro (IC) es de 162 ± 11 μSv/Gy a una distancia de 13 cm del IC. Se presentan igualmente valores de flujo y tasa de densidad de trazas en el cabezal del acelerador.
“…Al respecto, Barquero y colaboradores midieron con pares de TLD la fluencia de neutrones térmicos en el cabezal de un acelerador lineal de 18 MV, en donde también obtuvieron fluencia y dosis equivalente por neutrones térmicos en la mesa de tratamiento [13]. Similarmente en otras investigaciones se han calculado también dosis equivalente por neutrones posicionando pares de TLD en un fantoma de calibración [14][15][16][17].…”
Mediante detectores de trazas tipo CR-39 se determinó la dosis equivalente ambiental H*(10) por neutrones rápidos y térmicos en un acelerador Varian Clinac 2300 que opera en el rango de 6-18 MV. Mediciones preliminares fueron efectuadas ante una fuente moderada de neutrones 252Cf para obtener la respuesta del detector según el rango de energía. Se obtuvieron valores de tasa de densidad de trazas, flujo y dosis equivalente ambiental H*(10) por neutrones rápidos y térmicos en la mesa de tratamiento del recinto. Se determinó que la dosis equivalente ambiental H*(10) por unidad de dosis Gy en el isocentro (IC) es de 162 ± 11 μSv/Gy a una distancia de 13 cm del IC. Se presentan igualmente valores de flujo y tasa de densidad de trazas en el cabezal del acelerador.
The purpose of this work was to investigate by Monte Carlo method the adjustment of photon beams delivered by the medical LINear ACcelerator (LINAC) Elekta Synergy MLCi2. This study presents an optimization of the Gaussian distribution parameters of the accelerated electrons before the target simulated by two Monte Carlo codes and for three beams. The photon (X-ray) beam is produced by the interaction of accelerated electrons with the LINAC target. The electrons are accelerated by a potential difference created between the anode and the cathode of the gun and directed towards the target. In the Monte Carlo simulation, it is necessary to setup the spectrum parameters of the generated electrons to simulate the X-ray dose distribution. In this study, we modeled the LINAC geometry for photon beams 18MV and 6MV in cases Flattened (FF) and Flattening-Filter-Free (FFF). The Monte Carlo simulations are based on G4Linac_MT and GATE codes. The results of the optimized configurations determined after more than 20 tests for each beam energy show a very good agreement with the experimental measurements for different irradiation fields for the depth (PDD) and lateral (Profile) dose distribution. In all Monte Carlo calculations performed in this study, the statistical uncertainty is less than 2%. The results were also in very good agreement in terms of γ-index analysis, for the 3%/3mm and 2%/2mm criteria.
Photon energy is higher than the (γ,n) threshold, allowing it to interact with the nuclei of materials with high z properties and liberate fast neutrons. This represents a potentially harmful source of radiation for humans and the environment. This study validated the Monte Carlo simulation, using the particle and heavy-ion transport code system (PHITS) on a TrueBeam 10-MV linear particle accelerator’s head shielding model and then used this PHITS code to simulate a photo-neutron spectrum for the transport of the beam. The results showed that, when comparing the simulated to measured PDD and crosslines, 100% of the γ-indexes were <1 (γ3%/3mm) for both simulations, for both phase-space data source and a mono energy source. Neutron spectra were recorded in all parts of the TrueBeam’s head, as well as photon neutron spectra at three points on the beamline.
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