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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

Photoneutron dose equivalent at different distances from the maze entrance
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Figure 7: Photoneutron dose equivalent at different distances from the maze entrance

Mentions: In order to estimate the amount of dose received to patient at maze, photoneutron dose equivalent was also calculated at different points in the maze. According to our results, the dimensions of irradiation fields have no effect on the neutron dose equivalent in the maze, so photoneutron dose equivalent for just 40×40 cm2 field size at air detector placed at different distances from the entrance were displayed figure 7. Given the results, the dose equivalent at the entrance of the maze was lower than at the other points in the maze. By increasing the distance from the entrance of treatment room, dose equivalent increased, so that at energy of 25 MV this value was 1100%, 180%, and 167% higher than at energies of 15 MV, 18 MV, and 20 MV, separately. It should be mentioned that these remarkable enhancement were due to the value of Q (the number of neutron produced at energy of 25MV per 1 Gy were 1100%, 180%, and 167% higher than at energies of 15 MV, 18 MV, and 20 MV, respectively).


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)

Photoneutron dose equivalent at different distances from the maze entrance
© Copyright Policy
Related In: Results  -  Collection

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

Figure 7: Photoneutron dose equivalent at different distances from the maze entrance
Mentions: In order to estimate the amount of dose received to patient at maze, photoneutron dose equivalent was also calculated at different points in the maze. According to our results, the dimensions of irradiation fields have no effect on the neutron dose equivalent in the maze, so photoneutron dose equivalent for just 40×40 cm2 field size at air detector placed at different distances from the entrance were displayed figure 7. Given the results, the dose equivalent at the entrance of the maze was lower than at the other points in the maze. By increasing the distance from the entrance of treatment room, dose equivalent increased, so that at energy of 25 MV this value was 1100%, 180%, and 167% higher than at energies of 15 MV, 18 MV, and 20 MV, separately. It should be mentioned that these remarkable enhancement were due to the value of Q (the number of neutron produced at energy of 25MV per 1 Gy were 1100%, 180%, and 167% higher than at energies of 15 MV, 18 MV, and 20 MV, respectively).

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