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    Biological and dosimetric characterisation of spatially fractionated proton minibeams. (2017)

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    Meyer et al_2017_Phys._Med._Biol._10.1088_1361-6560_aa950c.pdf (4.982Mb)
    Type of Content
    Journal Article
    UC Permalink
    http://hdl.handle.net/10092/15389
    
    Publisher's DOI/URI
    https://doi.org/10.1088/1361-6560/aa950c
    
    ISSN
    0031-9155
    Collections
    • Science: Journal Articles [1192]
    Authors
    Meyer J
    Stewart R
    Smith D
    Eagle J
    Lee E
    Marsh SH
    show all
    Abstract

    The biological effectiveness of proton beams varies with depth, spot size and lateral distance from the beam central axis. The aim of this work is to incorporate proton relative biological effectiveness (RBE) and equivalent uniform dose (EUD) considerations into comparisons of broad beam and highly modulated proton minibeams. A Monte Carlo model of a small animal proton beamline is presented. Dose and variable RBE is calculated on a per-voxel basis for a range of energies (30-109 MeV). For an open beam, the RBE values at the beam entrance ranged from 1.02-1.04, at the Bragg peak (BP) from 1.3 to 1.6, and at the distal end of the BP from 1.4 to 2.0. For a 50 MeV proton beam, a minibeam collimator designed to produce uniform dose at the depth of the BP peak, had minimal impact on the open beam RBE values at depth. RBE changes were observed near the surface when the collimator was placed flush with the irradiated object, due to a higher neutron contribution derived from proton interactions with the collimator. For proton minibeams, the relative mean RBE weighted entrance dose (RWD) was ~25% lower than the physical mean dose. A strong dependency of the EUD with fraction size was observed. For 20 Gy fractions, the EUD varied widely depending on the radiosensitivity of the cells. For radiosensitive cells, the difference was up to ~50% in mean dose and ~40% in mean RWD and the EUD trended towards the valley dose rather than the mean dose. For comparative studies of uniform dose with spatially fractionated proton minibeams, EUD derived from a per-voxel RWD distribution is recommended for biological assessments of reproductive cell survival and related endpoints.

    Keywords
    proton therapy; minibeam; variable relative biological effectiveness (RBE); linear energy transfer (LET); equivalent uniform dose (EUD); spatial modulation
    ANZSRC Fields of Research
    51 - Physical sciences::5105 - Medical and biological physics::510502 - Medical physics
    32 - Biomedical and clinical sciences::3211 - Oncology and carcinogenesis::321110 - Radiation therapy
    51 - Physical sciences::5107 - Particle and high energy physics::510703 - Particle physics
    Rights
    During the embargo period (the 12 month period from the publication of the Version of Record of this article), the Accepted Manuscript is fully protected by copyright and cannot be reused or reposted elsewhere. As the Version of Record of this article is going to be / has been published on a subscription basis, this Accepted Manuscript is available for reuse under a CC BY-NC-ND 3.0 licence after the 12 month embargo period. After the embargo period, everyone is permitted to use copy and redistribute this article for non-commercial purposes only, provided that they adhere to all the terms of the licence https://creativecommons.org/licences/by-nc-nd/3.0

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