The electron, photon, and neutron spectra produced during the interaction between monoenergetic electron beams (8, 10, 12, 15, and 18 MeV) and a 0.05 cm-thick tungsten scattering foil were estimated using Monte Carlo method. Incoming electrons is a pencil beam that after collide with the foil acquires a broader distribution peaked in the same direction of the incoming electrons. Electron spectra show the influence of the binding energy of electrons in the tungsten shells and the increase of the electron fluence. In the interaction between the electrons in the beam and the tungsten atoms in the foil, bremsstrahlung and characteristic photons are produced. These photons are also peaked in the same direction of the incoming beam, and the electron fluence increases as the energy of the electron beam raises. The electron and photon spectra have particles whose energy is larger than the binding energy of neutron in the nucleus. Thus neutron production was noticed for 10, 12, 15, and 18 MeV electron beam. The neutron fluence becomes larger as the energy of the electron beam increases, the neutron spectra are mainly evaporation neutrons for 10 and 12 MeV, and for 15 and 18 MeV knock-on neutrons are also produced. Neutrons are produced in the foil volume having a quasi-isotropic distribution.

Neutron production during the interaction of monoenergetic electrons with a Tungsten foil in the radiotherapeutic energy range

This study investigates electron contamination for 6 MV photon beams from an Elekta linear accelerator (linac) using Monte Carlo simulation. The linac head was simulated by the BEAMnrc code and the absorbed dose in a phantom was calculated using the DOSXYZnrc code. The parameters of the initial electron beams on the target, such as mean energy and radial intensity distribution, were determined by matching the calculated dose distributions with the measured dose (at 10 x 10 cm2 field size and 90 cm source-skin distance). The central axis depth-dose curves of electron contamination were calculated for various field sizes from 5 x 5 cm2 to 40 x 40 cm2. We investigated the components that generated the electron contamination for a field size of 10 x 10 cm2. The optimal initial electron beam energy was 6.3 MeV with a full-width half maximum (FWHM) of the radial intensity distribution of 1.0 mm. These parameters were found to be in good agreement with the measured data. Electron contamination increased as the field size increased. At a depth of 1.0 mm and field sizes of 5 x 5, 10 x 10, 20 x 20, 30 x 30, and 40 x 40 cm2, the doses from electron contamination were 3.71, 5.19, 14.39, 18.97 and 20.89 %, respectively. Electron contamination decreased with increased depth. At a depth of 15 mm, the electron contamination was about 1 %. It was mainly generated in the air column between the linac head and the phantom (3.65 %), the mirror (0.99 %), and the flattening filter (0.59 %) (for a depth of 1.0 mm and field size of 10 x 10 cm2).

/pdf/electron-contamination-for-6-mv-photon-beams-from-an-elekta-1vulethh05.pdf

Electron contamination for 6 MV photon beams from an Elekta linac: Monte Carlo simulation

https://journals.viamedica.pl/rpor/article/download/74110/54203

Monte carlo model and output factors of elekta infinity™ 6 and 10 MV photon beam.

https://www.tandfonline.com/doi/pdf/10.1080/16878507.2020.1828020

Monte Carlo simulation of X-ray room shielding in diagnostic radiology using PHITS code

Comparison between EGSnrc and MCNPX for X-ray target in 6 MV photon beam

Background: The lack of lateral electronic disequilibrium (LED) becomes a main problem in small field. This factor affects the dose in target volume cannot predict correctly. In addi\"on, u\"liza\"on of high-energy linear accelerator (10 MV) can emit some unwanted par\"cles (electron contamina\"on). Therefore, the aim of this study was to characterize head linear accelerator (linac) Varian Clinac iX 10 MV photon beam for square small field size (1×1, 2×2, 3×3, 4×4 and 5×5 cm 2 ) using Monte Carlo (MC) simula\"on. Materials and Methods: The commissioning process for this linac, has been conducted for field size 6×6, 10×10 and 20×20 cm 2 by comparing the measurement and MC simula\"on data. Head linac simula\"on was performed with BEAMnrc and dose calcula\"on with DOSXYZnrc. The phase space (phsp) data from BEAMnrc was analyzed using BEAMDP to get the par\"cles informa\"on in scoring plane. Results and Discussion: The sca6er angle of par\"cles depends on the field size. This factor affects the penumbra width in water phantom. On the other hand, PDD data show that the depth of maximum dose and penumbra width in small field shi:ed correspond with the number of sca6er par\"cle. The difference of rela\"ve output factor between measurement and MC results were found less than 2%. However, the 2% difference was s\"ll acceptable in photon beam dosimetry. Conclusion: From this simula\"on, the electron contamina\"on give contribu\"on in surface dose of water phantom about 13.0581% and less than 1% for field size 10×10 cm 2 and small field size, respec\"vely.

Monte carlo simulation of varian clinac iX 10 MV photon beam for small field dosimetry

The purpose of this study was to investigate the characteristics of electron contamination and Output Factors (OFs) from Varian Trilogy Clinac iX 6 MV photon beam at small field sizes. EGSnrc Monte Carlo (MC) code system was used to model the photon beam for this Linear Accelerator (Linac) head and analyze the electron contamination and OFs from this treatment head. The electron contamination was analyzed for field sizes of 1 × 1, 2 × 2, 3 × 3, 4 × 4, and 5 × 5 cm2. The number of electron contamination increases with increasing field sizes, but the maximum energy of the electron contamination stays constant (at around 1.87 MeV for each field size). The contaminants contribute to the dose at the surface of the water phantom (1–5 cm from the surface) for field size 4 × 4 and 5 × 5 cm2 and this dose decreases with depth. The OFs are simulated by EGSnrc code system and have a good agreement with measurement (deviation 3.45, 1.76, and 0.86 for field of 2, 3 and 4, respectively). This study presented th...

Monte Carlo study on electron contamination and output factors of small field dosimetry in 6 MV photon beam

High energy medical accelerators are commonly used in radiotherapy to increase the effectiveness of treatments. As we know neutrons can be emitted from a medical accelerator if there is an incident of X-ray that hits any of its materials. This issue becomes a point of view of many researchers. The neutron contamination has caused many problems such as image resolution and radiation protection for patients and radio oncologists. This study concerns the simulation of neutron contamination emitted from Varian Clinac iX 10 MV using Monte Carlo code system. As neutron production process is very complex, Monte Carlo simulation with MCNPX code system was carried out to study this contamination. The design of this medical accelerator was modelled based on the actual materials and geometry. The maximum energy of photons and neutron in the scoring plane was 10.5 and 2.239 MeV, respectively. The number and energy of the particles produced depend on the depth and distance from beam axis. From these results, it is pointed out that the neutron produced by linac 10 MV photon beam in a typical treatment is not negligible.

http://iopscience.iop.org/article/10.1088/1742-6596/694/1/012020/pdf

Mohamad Fahdillah Rhani

Papers

Monte carlo simulation of varian clinac iX 10 MV photon beam for small field dosimetry

Monte Carlo study on electron contamination and output factors of small field dosimetry in 6 MV photon beam

Monte carlo model and output factors of elekta infinity™ 6 and 10 MV photon beam.

Neutron contamination of Varian Clinac iX 10 MV photon beam using Monte Carlo simulation

Comparison between EGSnrc and MCNPX for X-ray target in 6 MV photon beam