Monte Carlo simulations of stray neutron radiation exposures in proton therapy

Zheng, Yuanshui; Newhauser, Wayne D.; Fontenot, Jonas D.; Koch, N; Mohan, Radhe

doi:10.1016/j.jnucmat.2006.12.016

Cited by 39 publications

(78 citation statements)

References 17 publications

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“…Specifically, it was used as a guide for the overall dimensions and the positions of the RMW, second scatterer and collimating system (Zheng et al 2007a, 2007b). However, we designed the RMW and second scatterer following the methods of Gottschalk et al (1991).…”

Section: Methodsmentioning

confidence: 99%

“…A schematic diagram of the nozzle simulated is shown in figure 1 (Newhauser et al 2007, Zheng 2007a, 2007b). It consists of an RMW, a second scatterer, a set of collimators and a retractable snout with a final field-defining aperture.…”

Section: Methodsmentioning

confidence: 99%

“…The reported neutron equivalent dose values per therapeutic dose 4 were significantly larger than those reported in more recent studies for other passive systems. These differences have not been resolved in the literature but may be traceable to the dose reporting methods as noted by Zheng (2007a). In addition, using Monte Carlo simulations, Agosteo et al (1998) estimated 10 −3 Gy per therapeutic Gy for deep-seated tumors treatments due to neutrons and photons for active scanning systems.…”

Section: Introductionmentioning

confidence: 99%

“…In one of their studies (Zheng et al 2007a), they estimated the neutron dose equivalent at various distances from isocenter. For forward angles, the neutron dose equivalent per therapeutic dose decreased with distance from isocenter.…”

Section: Introductionmentioning

confidence: 99%

“…The beam spreading system modeled in this work closely resembles that of The University of Texas M. D. Anderson Cancer Center (Newhauser et al 2007, Zheng et al 2007a, 2007b). The neutron energy spectrum and absorbed dose were investigated for this system as a function of neutron emission.…”

Section: Introductionmentioning

confidence: 99%

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Neutron production from beam-modifying devices in a modern double scattering proton therapy beam delivery system

2009

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In this work the neutron production in a passive beam delivery system was investigated. Secondary particles including neutrons are created as the proton beam interacts with beam shaping devices in the treatment head. Stray neutron exposure to the whole body may increase the risk that the patient develops a radiogenic cancer years or decades after radiotherapy. We simulated a passive proton beam delivery system with double scattering technology to determine the neutron production and energy distribution at 200 MeV proton energy. Specifically, we studied the neutron absorbed dose per therapeutic absorbed dose, the neutron absorbed dose per source particle and the neutron energy spectrum at various locations around the nozzle. We also investigated the neutron production along the nozzle's central axis. The absorbed doses and neutron spectra were simulated with the MCNPX Monte Carlo code. The simulations revealed that the range modulation wheel (RMW) is the most intense neutron source of any of the beam spreading devices within the nozzle. This finding suggests that it may be helpful to refine the design of the RMW assembly, e.g., by adding local shielding, to suppress neutron-induced damage to components in the nozzle and to reduce the shielding thickness of the treatment vault. The simulations also revealed that the neutron dose to the patient is predominated by neutrons produced in the field defining collimator assembly, located just upstream of the patient.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Neutron production from beam-modifying devices in a modern double scattering proton therapy beam delivery system

2009

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AAPM TG158: Measurement and calculation of doses outside the treated volume from external‐beam radiation therapy

et al. 2017

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The introduction of advanced techniques and technology in radiotherapy has greatly improved our ability to deliver highly conformal tumor doses while minimizing the dose to adjacent organs at risk. Despite these tremendous improvements, there remains a general concern about doses to normal tissues that are not the target of the radiation treatment; any "nontarget" radiation should be minimized as it offers no therapeutic benefit. As patients live longer after treatment, there is increased opportunity for late effects including second cancers and cardiac toxicity to manifest. Complicating the management of these issues, there are unique challenges with measuring, calculating, reducing, and reporting nontarget doses that many medical physicists may have limited experience with. Treatment planning systems become dramatically inaccurate outside the treatment field, necessitating a measurement or some other means of assessing the dose. However, measurements are challenging because outside the treatment field, the radiation energy spectrum, dose rate, and general shape of the dose distribution (particularly the percent depth dose) are very different and often require special consideration. Neutron dosimetry is also particularly challenging, and common errors in methodology can easily manifest as errors of several orders of magnitude. Task Group 158 was, therefore, formed to provide guidance for physicists in terms of assessing and managing nontarget doses. In particular, the report: (a) highlights major concerns with nontarget radiation; (b) provides a rough estimate of doses associated with different treatment approaches in clinical practice; (c) discusses the uses of dosimeters for measuring photon, electron, and neutron doses; (d) discusses the use of calculation techniques for dosimetric evaluations; (e) highlights techniques that may be considered for reducing nontarget doses; (f) discusses dose reporting; and (g) makes recommendations for both clinical and research practice.

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A Monte Carlo‐based analytic model of neutron dose equivalent for a mevion gantry‐mounted passively scattered proton system for craniospinal irradiation

Baradaran‐Ghahfarokhi

Reynoso

Sun

et al. 2020

Medical Physics

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Purpose: To calculate in-and out-of-field neutron spectra and dose equivalent, using Monte Carlo (MC) simulation, for a Mevion gantry-mounted passively scattered proton system in craniospinal irradiation. An analytical model based on the MC calculations that estimates in-and out-of-field neutron dose equivalent from proton Craniospinal irradiation (CSI) was also developed. Methods: The MCNPX MC code was used to simulate a Mevion S250 proton therapy system. The simulated proton depth doses and profiles for pristine and spread-out Bragg peaks were benchmarked against the measured data. Previous measurements using extended-range Bonner spheres were used to verify the calculated neutron spectra and dose equivalent. Using the benchmarked results as a reference condition, a correction-based analytical model was reconstructed by fitting the data to derive model parameters at 95% confidence interval. Sensitivity analysis of brass aperture opening, thickness of the Lucite (PMMA) range compensator, and modulation width was performed to obtain correction parameters for nonreference conditions. Results: For the neutron dose equivalent per therapeutic proton dose, the MCNPX calculated dose equivalent matched the measured values to within 8%. The benchmarked neutron dose equivalent at the isocenter was 41.2 and 20.8 mSv/Gy, for cranial and spinal fields, respectively. For in-and outof-field neutron dose calculations, the correction-based analytical model showed up to 17% discrepancy compared to the MC calculations. The correction factors may provide a conservative estimation of neutron dose, especially for depth ≤ 5 cm and regions underneath the brass aperture. Conclusion: The proposed analytical model can be used to estimate the contribution of the neutron dose to the overall CSI treatment dose. Moreover, the model can be employed to estimate the neutron dose to the implantable cardiac electronic devices.

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Monte Carlo simulations of stray neutron radiation exposures in proton therapy

Cited by 39 publications

References 17 publications

Neutron production from beam-modifying devices in a modern double scattering proton therapy beam delivery system

Neutron production from beam-modifying devices in a modern double scattering proton therapy beam delivery system

AAPM TG158: Measurement and calculation of doses outside the treated volume from external‐beam radiation therapy

A Monte Carlo‐based analytic model of neutron dose equivalent for a mevion gantry‐mounted passively scattered proton system for craniospinal irradiation

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