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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 absorbed dose (mGy/Gy) distribution around the prostate in the prostate treatment for 15 MV accelerator
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Figure 9: Photoneutron absorbed dose (mGy/Gy) distribution around the prostate in the prostate treatment for 15 MV accelerator

Mentions: Finally, the mesh tally was utilized to define the energy deposition distribution around the target volume of treatment. Then the stored energy in each voxel was divided by corresponding density, and the absorbed dose was calculated in the phantom. The size of each scoring cell of the mesh tally in the phantom was set to 0.2137 cm × 0.2137 cm × 0.8 cm as the same of voxel dimensions. Absorbed dose distribution around the prostate for energy of 15 MV is shown in the figure 9. According to the x-z view of this figure, the maximum absorbed dose was in the target volume, but in the surrounding tissue the value of absorbed dose was in the range of 14×10-3-18×10-3 mGy/Gy. In other view(x-y plan), it was observed that the amount of absorbed dose in the skin and tissues close to the body surface was significant and ranged from14×10-3 to 24×10-3 mGy/Gy. By increasing the depth and approaching to the back of body, absorbed dose decreased to 2×10-3 mGy/Gy. Unexpectedly, this reduction was not observed for two regions which were located in front of the hands and their absorbed doses were greater than the other positions of back of the body. This is due to the fact that hands acted as reflector and scattered the photoneutrons toward the body, so they caused enhancement in received doses in these regions. Therefore, to prevent this from happening it was suggested that patients wereplaced in the arm raised position during the prostate treatment.


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 absorbed dose (mGy/Gy) distribution around the prostate in the prostate treatment for 15 MV accelerator
© Copyright Policy
Related In: Results  -  Collection

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

Figure 9: Photoneutron absorbed dose (mGy/Gy) distribution around the prostate in the prostate treatment for 15 MV accelerator
Mentions: Finally, the mesh tally was utilized to define the energy deposition distribution around the target volume of treatment. Then the stored energy in each voxel was divided by corresponding density, and the absorbed dose was calculated in the phantom. The size of each scoring cell of the mesh tally in the phantom was set to 0.2137 cm × 0.2137 cm × 0.8 cm as the same of voxel dimensions. Absorbed dose distribution around the prostate for energy of 15 MV is shown in the figure 9. According to the x-z view of this figure, the maximum absorbed dose was in the target volume, but in the surrounding tissue the value of absorbed dose was in the range of 14×10-3-18×10-3 mGy/Gy. In other view(x-y plan), it was observed that the amount of absorbed dose in the skin and tissues close to the body surface was significant and ranged from14×10-3 to 24×10-3 mGy/Gy. By increasing the depth and approaching to the back of body, absorbed dose decreased to 2×10-3 mGy/Gy. Unexpectedly, this reduction was not observed for two regions which were located in front of the hands and their absorbed doses were greater than the other positions of back of the body. This is due to the fact that hands acted as reflector and scattered the photoneutrons toward the body, so they caused enhancement in received doses in these regions. Therefore, to prevent this from happening it was suggested that patients wereplaced in the arm raised position during the prostate treatment.

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