Grid therapy vs. conventional radiotherapy – 18 MV treatments: Photoneutron contamination along the maze of a linac bunker

Karimi, Amir Hossein; Vega-Carrillo, Héctor René

doi:10.1016/j.apradiso.2020.109064

Cited by 6 publications

(7 citation statements)

References 20 publications

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“…Fig 6A shows the neutron energy spectrum at the IC for the open and the grid fields. The appearance of the spectrum is similar to the corresponding cases in Karimi and Vega-Carrillo's study on 18 MV photons [21]. It is noticeable that there are two peaks, one related to the fast neutrons (the higher peak) and the other related to the thermal neutrons (the shorter peak).…”

Section: Neutron Spectrometry Inside the Mazesupporting

confidence: 80%

“…Nevertheless, independent of detector location, F n and H � n ð10Þ at the end of the maze (detector 1) in SFGRT is nearly 1.5 times that of CFRT. In comparison with data reported by Karimi and Vega-Carrillo's study on 18 MV photons [21], it can be found that independent of treatment modality and detector location, F n and H � n ð10Þ in SFGRT with 15 MV photons is almost 70% lower than in 18 MV photons. Therefore, given the concerns about 18 MV SFGRT, 15 MV SFGRT can be considered as an alternative from the radiation protection point of view.…”

Section: Ambient Dose Equivalent Of Contaminant Neutronssupporting

confidence: 49%

“…Cerrobend, lead and brass were used to model the grids. To compare the spectrum of neutron contamination between two photon beams (15 MV vs. 18 MV) under a similar condition, the bunker used by Karimi and Vega-Carrillo [21] was modeled as is shown in Fig 2 . The density of 2.35 g/cm 3 was considered for the concrete walls composed by O (49.83%), Si (31.58%), Ca (8.26%), Al (4.56%), K (1.92%), Na (1.71%), Fe (1.22%), and H (0.92%).…”

Section: Monte Carlo Simulationmentioning

confidence: 99%

“…Accordingly, Karimi et al [9] showed that the F n PLOS ONE inside the large field sizes for SFGRT with lead block is, on average, 23% higher than in CFRT. A similar analysis on neutron contamination inside the maze of radiotherapy room showed that neutron ambient dose equivalent, H � n ð10Þ, was up to 50% higher than in CFRT [21]. From the perspective of radiation protection, SFGRT with 15 MV photons was proposed recently as an alternative [9].…”

Section: Introductionmentioning

confidence: 99%

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How much should you worry about contaminant neutrons in spatially fractionated grid radiation therapy?

et al. 2023

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Neutron contamination in radiation therapy is of concern in treatment with high-energy photons (> 10 MV). With the development of new radiotherapy modalities such as spatially fractionated grid radiation therapy (SFGRT) or briefly grid radiotherapy, more studies are required to evaluate the risks associated with neutron contamination. In 15 MV SFGRT, high-Z materials such as lead and cerrobend are used as the block on the tray of linear accelerator (linac) which can probably increase the photoneutron production. On the other hand, the high-dose fractions (10–20 Gy) used in SFGRT can induce high neutron contamination. The current study was devoted to addressing these concerns via compression of neutron fluence (Φn) and ambient dose equivalent (Hn*(10)) at the patient table and inside the maze between SFGRT and conventional fractionated radiation therapy (CFRT). The main components of the 15 MV Siemens Primus equipped with different grids and located inside a typical radiotherapy bunker were simulated by the MCNPX® Monte Carlo code. Evidence showed that the material used for grid construction does not significantly increase neutron contamination inside the maze. However, at the end of the maze, neutron contamination in SFGRT is significantly higher than in CFRT. In this regard, a delay time of 15 minutes after SFGRT is recommended for all radiotherapy staff before entering the maze. It can be also concluded that Hn*(10) at the patient table is at least 10 times more pronounced than inside the maze. Therefore, the patient is more at risk of neutrons compared to the staff. The Hn*(10) at the isocenter in SFGRT with grids made of lead and cerrobend was nearly equal to CFRT. Nevertheless, it was dramatically lower than in CFRT by 30% if the brass grid is used. Accordingly, SFGRT with the brass grid is recommended, from radiation protection aspects.

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Section: Neutron Spectrometry Inside the Mazesupporting

confidence: 80%

Section: Ambient Dose Equivalent Of Contaminant Neutronssupporting

confidence: 49%

Section: Monte Carlo Simulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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How much should you worry about contaminant neutrons in spatially fractionated grid radiation therapy?

et al. 2023

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“…In high energy treatments (>8 MV) [9], due to the occurrence of giant dipole resonance (n, γ) between photons and linac head components of high atomic number composition (e.g. lead and tungsten), a significant portion of the neutron production (in order of 10 12 neutrons per 1 Gy photon dose delivered to the isocenter) is nonenegligible [10][11][12]. Since neutrons are high-LET (Linear Energy Transfer) particles, their destructive effects on radiosensitive tissues and organs are significant.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo evaluation of out-of-field dose in 18 MV pelvic radiotherapy using a simplified female MIRD phantom

Geraily¹,

Elmtalab²,

Mohammadi³

et al. 2021

Biomed. Phys. Eng. Express

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This study was devoted to determining the unwanted dose due to scattered photons to the out-of-field organs and subsequently estimate the risk of secondary cancers in the patients undergoing pelvic radiotherapy. A typical 18 MV Medical Linear Accelerator (Varian Clinac 2100 C/D) was modeled using MCNPX® code to simulate pelvic radiotherapy with four treatment fields: anterior-posterior, posterior-anterior, right lateral, left lateral. Dose evaluation was performed inside Medical Internal Radiation Dose (MIRD) revised female phantom. The average photon equivalent dose in out-of-field organs is 8.53 mSv Gy−1, ranging from 0.17 to 72.11 mSv Gy−1, respectively, for the organs far from the Planning Treatment Volume (Brain) and those close to the treatment field (Colon). Evidence showed that colon with 4.3049% and thyroid with 0.0020% have the highest and lowest risk of secondary cancer, respectively. Accordingly, this study introduced the colon as an organ with a high risk of secondary cancer which should be paid more attention in the follow-up of patients undergoing pelvic radiotherapy. The authors believe that this simple Monte Carlo (MC) model can be also used in other radiotherapy plans and mathematical phantoms with different ages (from childhood to adults) to estimate the out-of-field dose. The extractable information by this simple MC model can be also employed for providing libraries for user-friendly applications (e.g. ‘.apk’) which in turn increase the public knowledge about fatal cancer risk after radiotherapy and subsequently decrease the concerns in this regard among the public.

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Feasibility of 18-MV grid therapy from radiation protection aspects: unwanted dose and fatal cancer risk caused by photoneutrons and scattered photons

Karimi

Mirian

Mahmoudi

et al. 2022

Computer Methods and Programs in Biomedicine

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Grid therapy vs. conventional radiotherapy – 18 MV treatments: Photoneutron contamination along the maze of a linac bunker

Cited by 6 publications

References 20 publications

How much should you worry about contaminant neutrons in spatially fractionated grid radiation therapy?

How much should you worry about contaminant neutrons in spatially fractionated grid radiation therapy?

Monte Carlo evaluation of out-of-field dose in 18 MV pelvic radiotherapy using a simplified female MIRD phantom

Feasibility of 18-MV grid therapy from radiation protection aspects: unwanted dose and fatal cancer risk caused by photoneutrons and scattered photons

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