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    Biological and dosimetric characterisation of spatially fractionated proton minibeams.

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    Embargoed until November 22nd 2018 (4.982Mb)
    Author
    Meyer J
    Stewart R
    Smith D
    Eagle J
    Lee E
    Marsh SH
    Date
    2017
    Permanent Link
    http://hdl.handle.net/10092/15389

    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.

    Subjects
    proton therapy
     
    minibeam
     
    variable relative biological effectiveness (RBE)
     
    linear energy transfer (LET)
     
    equivalent uniform dose (EUD)
     
    spatial modulation
     
    Field of Research::02 - Physical Sciences::0299 - Other Physical Sciences::029903 - Medical Physics
     
    Field of Research::11 - Medical and Health Sciences::1112 - Oncology and Carcinogenesis::111208 - Radiation Therapy
     
    Field of Research::02 - Physical Sciences::0202 - Atomic, Molecular, Nuclear, Particle and Plasma Physics::020203 - Particle Physics
    Collections
    • Science: Journal Articles [906]

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