open access

Vol 25, No 2 (2020)
Original research articles
Published online: 2020-03-01
Submitted: 2019-07-12
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Application of the phase-space distribution approach of Monte Carlo for radiation contamination dose estimation from the (n,γ), (γ,n) nuclear reactions and linac leakage photons in the megavoltage radiotherapy facility

Amir Ghasemi-Jangjoo, Hosein Ghiasi
DOI: 10.1016/j.rpor.2020.01.006
·
Rep Pract Oncol Radiother 2020;25(2):233-240.

open access

Vol 25, No 2 (2020)
Original research articles
Published online: 2020-03-01
Submitted: 2019-07-12

Abstract

Aim

The aim of this study was to characterize the radiation contamination inside and outside the megavoltage radiotherapy room.

Background

Radiation contamination components in the 18MV linac room are the secondary neutron, prompt gamma ray, electron and linac leakage radiation.

Materials and Methods

An 18MV linac modeled in a typical bunker employing the MCNPX code of Monte Carlo. For fast calculation, phase-space distribution (PSD) file modeling was applied and the calculations were conducted for the radiation contamination components dose and spectra at 6 locations inside and outside the bunker.

Results

The results showed that the difference of measured and calculated percent depth-dose (PDD) and photo beam-profile (PBP) datasets were lower than acceptable values. At isocenter, the obtained photon dose and neutron fluence were 2.4×10−14 Gy/initial e° and 2.22×10-8 n°/cm2, respectively. Then, neutron apparent source strength (QN) value was found as 1.34×1012 n°/Gy X at isocenter and the model verified to photon and neutron calculations. A surface at 2cm below the flattening filter was modeled as phase-space (PS) file for PDD and PBP calculations. Then by use of a spherical cell in the center of the linac target as a PS surface, contaminant radiations dose, fluence and spectra were estimated at 6 locations in a considerably short time, using the registered history of all particles and photons in the 13GB PSD file as primary source in the second step.

Conclusion

Designing the PSD file in MC modeling helps user to solve the problems with complex geometry and physics precisely in a shorter run-time.

Abstract

Aim

The aim of this study was to characterize the radiation contamination inside and outside the megavoltage radiotherapy room.

Background

Radiation contamination components in the 18MV linac room are the secondary neutron, prompt gamma ray, electron and linac leakage radiation.

Materials and Methods

An 18MV linac modeled in a typical bunker employing the MCNPX code of Monte Carlo. For fast calculation, phase-space distribution (PSD) file modeling was applied and the calculations were conducted for the radiation contamination components dose and spectra at 6 locations inside and outside the bunker.

Results

The results showed that the difference of measured and calculated percent depth-dose (PDD) and photo beam-profile (PBP) datasets were lower than acceptable values. At isocenter, the obtained photon dose and neutron fluence were 2.4×10−14 Gy/initial e° and 2.22×10-8 n°/cm2, respectively. Then, neutron apparent source strength (QN) value was found as 1.34×1012 n°/Gy X at isocenter and the model verified to photon and neutron calculations. A surface at 2cm below the flattening filter was modeled as phase-space (PS) file for PDD and PBP calculations. Then by use of a spherical cell in the center of the linac target as a PS surface, contaminant radiations dose, fluence and spectra were estimated at 6 locations in a considerably short time, using the registered history of all particles and photons in the 13GB PSD file as primary source in the second step.

Conclusion

Designing the PSD file in MC modeling helps user to solve the problems with complex geometry and physics precisely in a shorter run-time.

Get Citation

Keywords

Phase-space distribution; Monte Carlo simulation; Dose equivalent; Photon; Neutron

About this article
Title

Application of the phase-space distribution approach of Monte Carlo for radiation contamination dose estimation from the (n,γ), (γ,n) nuclear reactions and linac leakage photons in the megavoltage radiotherapy facility

Journal

Reports of Practical Oncology and Radiotherapy

Issue

Vol 25, No 2 (2020)

Pages

233-240

Published online

2020-03-01

DOI

10.1016/j.rpor.2020.01.006

Bibliographic record

Rep Pract Oncol Radiother 2020;25(2):233-240.

Keywords

Phase-space distribution
Monte Carlo simulation
Dose equivalent
Photon
Neutron

Authors

Amir Ghasemi-Jangjoo
Hosein Ghiasi

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