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A Monte Carlo Study for Photoneutron Dose Estimations around the High-Energy Linacs.

Mohammadi N, Miri-Hakimabad SH, Rafat-Motavalli L - J Biomed Phys Eng (2014)

Bottom Line: The results of dose calculations at the isocenter and maze showed that photoneutron dose decreases as the function of distance from the isocenter and increases with increasing the distance from the entrance maze.It is concluded that the simplified model of linac head is a useful and reliable method in dosimetry calculations.Calculations illustrated that the photoneutron dose is not negligible and duo to its harmful biological effects on body, it should be considered in the treatment plans.

View Article: PubMed Central - PubMed

Affiliation: Physics Department, Faculty of Sciences, Ferdowsi University of Mashhad, Iran.

ABSTRACT

Background: High-energy linear accelerator (linac) is a valuable tool and the most commonly used device for external beam radiation treatments in cancer patients. In the linac head, high-energy photons with energies above the threshold of (γ,n) interaction produce photoneutrons. These photoneutrons deliver the extra dose to the patients undergoing radiation treatment and increase the risk of secondary cancer.

Objective: In this study, a simplified model of the linac head was simulated and photoneutron dose equivalent was calculated at the isocenter and maze in the sphere detector. In addition, the absorbed and equivalent dose of photoneutron were estimated in the some organs of the phantom.

Methods: The simulations were made using the Monte Carlo code. The ICRP reference adult male voxel phantom was used as the human body model for dosimetry calculations.

Results: The results of dose calculations at the isocenter and maze showed that photoneutron dose decreases as the function of distance from the isocenter and increases with increasing the distance from the entrance maze.

Conclusion: It is concluded that the simplified model of linac head is a useful and reliable method in dosimetry calculations. Calculations illustrated that the photoneutron dose is not negligible and duo to its harmful biological effects on body, it should be considered in the treatment plans.

No MeSH data available.


Related in: MedlinePlus

The simplified model of linac head and voxel phantom in MCNPX simulation
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Figure 2: The simplified model of linac head and voxel phantom in MCNPX simulation

Mentions: The detailed geometry of linac is not always available. So, to confront this limitation, a simplified model of linac was simulated by Monte Carlo N-Particle (MCNP) to study neutron transport around the linac. This approach was used by other authors successfully[6-9]. In the linac head, the main source of photoneutrons is the reactions between photons and tungsten. Therefore, the simplified geometry of the head was simulated as 10 cm-thick spherical shell of tungsten with an air conical aperture. The point-like source of the photoneutron with spectra given by eq.1 was located in the center shell. The average photoneutron energies of these spectra were 1.15, 1.25, 1.31, and 1.46 MeV for 15, 18, 20, and 25 MV, respectively. In order to simulate the different radiation field sizes a suitable angle of cone was considered. The used photoneutron spectrum and simplified model of the simulated head were shown in figures 1 and 2.


A Monte Carlo Study for Photoneutron Dose Estimations around the High-Energy Linacs.

Mohammadi N, Miri-Hakimabad SH, Rafat-Motavalli L - J Biomed Phys Eng (2014)

The simplified model of linac head and voxel phantom in MCNPX simulation
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4289520&req=5

Figure 2: The simplified model of linac head and voxel phantom in MCNPX simulation
Mentions: The detailed geometry of linac is not always available. So, to confront this limitation, a simplified model of linac was simulated by Monte Carlo N-Particle (MCNP) to study neutron transport around the linac. This approach was used by other authors successfully[6-9]. In the linac head, the main source of photoneutrons is the reactions between photons and tungsten. Therefore, the simplified geometry of the head was simulated as 10 cm-thick spherical shell of tungsten with an air conical aperture. The point-like source of the photoneutron with spectra given by eq.1 was located in the center shell. The average photoneutron energies of these spectra were 1.15, 1.25, 1.31, and 1.46 MeV for 15, 18, 20, and 25 MV, respectively. In order to simulate the different radiation field sizes a suitable angle of cone was considered. The used photoneutron spectrum and simplified model of the simulated head were shown in figures 1 and 2.

Bottom Line: The results of dose calculations at the isocenter and maze showed that photoneutron dose decreases as the function of distance from the isocenter and increases with increasing the distance from the entrance maze.It is concluded that the simplified model of linac head is a useful and reliable method in dosimetry calculations.Calculations illustrated that the photoneutron dose is not negligible and duo to its harmful biological effects on body, it should be considered in the treatment plans.

View Article: PubMed Central - PubMed

Affiliation: Physics Department, Faculty of Sciences, Ferdowsi University of Mashhad, Iran.

ABSTRACT

Background: High-energy linear accelerator (linac) is a valuable tool and the most commonly used device for external beam radiation treatments in cancer patients. In the linac head, high-energy photons with energies above the threshold of (γ,n) interaction produce photoneutrons. These photoneutrons deliver the extra dose to the patients undergoing radiation treatment and increase the risk of secondary cancer.

Objective: In this study, a simplified model of the linac head was simulated and photoneutron dose equivalent was calculated at the isocenter and maze in the sphere detector. In addition, the absorbed and equivalent dose of photoneutron were estimated in the some organs of the phantom.

Methods: The simulations were made using the Monte Carlo code. The ICRP reference adult male voxel phantom was used as the human body model for dosimetry calculations.

Results: The results of dose calculations at the isocenter and maze showed that photoneutron dose decreases as the function of distance from the isocenter and increases with increasing the distance from the entrance maze.

Conclusion: It is concluded that the simplified model of linac head is a useful and reliable method in dosimetry calculations. Calculations illustrated that the photoneutron dose is not negligible and duo to its harmful biological effects on body, it should be considered in the treatment plans.

No MeSH data available.


Related in: MedlinePlus