Spectra of photoneutrons produced by high-energy X-ray radiotherapy linacs

Králı́k, M.; Turek, K.; Vondráček, Vladimír

doi:10.1093/rpd/ncn278

Cited by 22 publications

(14 citation statements)

References 5 publications

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“…From Table 1 , one can note a good agreement achieved between the obtained results and the related values in the literature. [ 19 34 35 36 37 ] It can also see, the average relative difference of our results with literature is 5.4% and 20.1% for the flux and the ambient dose equivalent of neutrons, respectively. These differences are reasonable, because the type of study (measurement/simulation), cross-section libraries for photoneutrons production, as well as the treatment room geometries differed.…”

Section: Discussionsupporting

confidence: 52%

Photoneutron dose estimation in GRID therapy using an anthropomorphic phantom: A monte carlo study

et al. 2018

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Background:In the past, GRID therapy was used as a treatment modality for the treatment of bulky and deeply seated tumors with orthovoltage beams. Now and with the introduction of megavoltage beams to radiotherapy, some of the radiotherapy institutes use GRID therapy with megavoltage photons for the palliative treatment of bulky tumors. Since GRID can be a barrier for weakening the photoneutrons produced in the head of medical linear accelerators (LINAC), as well as a secondary source for producing photoneutrons, therefore, in terms of radiation protection, it is important to evaluate the GRID effect on photoneutron dose to the patients.Methods:In this study, using the Monte Carlo code MCNPX, a full model of a LINAC was simulated and verified. The neutron source strength of the LINAC (Q), the distributions of flux (φ), and ambient dose equivalent (H*[10]) of neutrons were calculated on the treatment table in both cases of with/without the GRID. Finally, absorbed dose and dose equivalent of neutrons in some of the tissues/organs of MIRD phantom were computed with/without the GRID.Results:Our results indicate that the GRID increases the production of the photoneutrons in the LINAC head only by 0.3%. The calculations in the MIRD phantom show that neutron dose in the organs/tissues covered by the GRID is on average by 48% lower than conventional radiotherapy. In addition, in the uncovered organs (by the GRID), this amount is reduced to 25%.Conclusion:Based on the findings of this study, in GRID therapy technique compared to conventional radiotherapy, the neutron dose in the tissues/organs of the body is dramatically reduced. Therefore, there will be no concern about the GRID effect on the increase of unwanted neutron dose, and consequently the risk of secondary cancer.

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Section: Discussionsupporting

confidence: 52%

Photoneutron dose estimation in GRID therapy using an anthropomorphic phantom: A monte carlo study

et al. 2018

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“…The third neutron source was the 18 MV photon beam of Varian 2100 C/D medical linear accelerator ( Fig. 2a) obtained from other studies [3,31,32]. Finally, to compare our MC results with experimental measurements and to test the designed and fabricated nanoshields, the experimental measurements were performed with a neutron source of an Am-Be in the laboratory (Fig.…”

Section: Monte Carlo Simulationmentioning

confidence: 99%

Design and fabrication of a Nano-based neutron shield for fast neutrons from medical linear accelerators in radiation therapy

et al. 2020

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Background: Photo-neutrons are produced at the head of the medical linear accelerators (linac) by the interaction of high-energy photons, and patients receive a whole-body-absorbed dose from these neutrons. The current study aimed to find an efficient shielding material for fast neutrons. Methods: Nanoparticles (NPs) of Fe 3 O 4 and B 4 C were applied in a matrix of silicone resin to design a proper shield against fast neutrons produced by the 18 MeV photon beam of a Varian 2100 C/D linac. Neutron macroscopic cross-sections for three types of samples were calculated by the Monte Carlo (MC) method and experimentally measured for neutrons of an Am-Be source. The designed shields in different concentrations were tested by MCNPX MC code, and the proper concentration was chosen for the experimental test. A shield was designed with two layers, including nano-iron oxide and a layer of nano-boron carbide for eliminating fast neutrons. Results: MC simulation results with uncertainty less than 1% showed that for discrete energies and 50% nanomaterial concentration, the macroscopic cross-sections for iron oxide and boron carbide at the energy of 1 MeV were 0.36 cm − 1 and 0.32 cm − 1 , respectively. For 30% nanomaterial concentration, the calculated macroscopic cross-sections for iron oxide and boron carbide shields for Am-Be spectrum equaled 0.12 cm − 1 and 0.15 cm − 1 , respectively, while they are 0.15 cm − 1 and 0.18 cm − 1 for the linac spectrum. In the experiment with the Am-Be spectrum, the macroscopic cross-sections for 30% nanomaterial concentration were 0.17 ± 0.01 cm − 1 for iron oxide and 0.21 ± 0.02 cm − 1 for boron carbide. The measured transmission factors for 30% nanomaterial concentration with the Am-Be spectrum were 0.71 ± 0.01, 0.66 ± 0.02, and 0.62 ± 0.01 for the iron oxide, boron carbide, and double-layer shields, respectively. In addition, these values were 0.74, 0.69, and 0.67, respectively, for MC simulation for the linac spectrum at the same concentration and thickness of 2 cm. Conclusion: Results achieved from MC simulation and experimental tests were in a satisfactory agreement. The difference between MC and measurements was in the range of 10%. Our results demonstrated that the designed double-layer shield has a superior macroscopic cross-section compared with two single-layer nanoshields and more efficiently eliminates fast photo-neutrons.

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“…5,10,23,25,26 MC methods have been employed extensively to evaluate the photoneutron characteristics in radiation therapy. [26][27][28][29][30] MC studies have shown that neutron source strength or Q value varies with linac model, location of scoring cell, field size and modeling geometry.…”

Section: Photoneutron Production In Linac Headmentioning

confidence: 99%

A review on photoneutrons characteristics in radiation therapy with high-energy photon beams

Naseri

Mesbahi

2010

Reports of Practical Oncology & Radiotherapy

105

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In radiation therapy with high-energy photon beams (E > 10 MeV) neutrons are generated mainly in linacs head thorough (γ,n) interactions of photons with nuclei of high atomic number materials that constitute the linac head and the beam collimation system. These neutrons affect the shielding requirements in radiation therapy rooms and also increase the out-of-field radiation dose of patients undergoing radiation therapy with high-energy photon beams. In the current review, the authors describe the factors influencing the neutron production for different medical linacs based on the performed measurements and Monte Carlo studies in the literature.

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Spectra of photoneutrons produced by high-energy X-ray radiotherapy linacs

Cited by 22 publications

References 5 publications

Photoneutron dose estimation in GRID therapy using an anthropomorphic phantom: A monte carlo study

Photoneutron dose estimation in GRID therapy using an anthropomorphic phantom: A monte carlo study

Design and fabrication of a Nano-based neutron shield for fast neutrons from medical linear accelerators in radiation therapy

A review on photoneutrons characteristics in radiation therapy with high-energy photon beams

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