Radiation quality of a tomotherapy photon fan beam.
Tomotherapy, a novel radiotherapy technique, uses narrow fan beams for cancer patient treatment. Photon energy spectra for a rectangular 10 x 1 cm2 photon beam were analyzed in central axis and penumbra regions at depths of 3 to 10 cm in a water phantom. A 6 MV beam of a Varian 2100C/D Linear Accelerator was modeled using BEAM99 Monte Carlo calculations to simulate energy transport in a water phantom. Arrays of 4 x 2 mm2 scoring regions were arranged to cover the central axis and penumbra areas. Radiation quality factors were calculated based on dose-mean linear energy transfer. Although there appears to be a trend towards higher quality factor values in the penumbra area, this change is fairly small, at most 3% in penumbra region. We conclude that change in radiation quality is not likely to be an issue in a tomotherapeutic approach when 6 MV x rays are used.
Moiseenko
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London Regional Cancer Centre, 790 Commissioners Road East, London, Ontario N6A 4L6, Canada.
Mulligan
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M
Kron
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T
D004307:Dose-Response Relationship, Radiation; D009010:Monte Carlo Method; D009369:Neoplasms / Q000532:radiotherapy*; D017785:Photons / Q000627:therapeutic use*; D011878:Radiotherapy / Q000295:instrumentation* / Q000379:methods