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USE OF A PETROLEUM-BASED BOLUS FOR PHOTON RADIATION THERAPY OF DISTAL EXTREMITIES IN DOGS

Authors

  • MONIQUE N. MAYER,

    1. Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5B4,
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  • HIROTO YOSHIKAWA,

    1. Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5B4,
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  • LEO MORIARITY,

    1. Tom Baker Cancer Centre, School of Radiation Therapy, 1331 29 Street NW, Calgary, Alberta, Canada T2N 4N2, and
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  • NARINDER SIDHU

    1. Department of Medical Physics, Saskatoon Cancer Centre, Saskatoon, Saskatchewan, Canada S7N 4H4
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Address correspondence and reprint requests to Monique N. Mayer, at the above address. E-mail: monique.mayer@usask.ca

Abstract

While skin sparing is an advantage of megavoltage beams, in certain clinical situations the planning target volume includes the skin surface and a skin sparing effect is not desirable. A tissue equivalent material, termed build up bolus, is used in these situations to provide adequate absorbed dose at the surface of the skin. However, an irregular patient contour can lead to air gaps between the build up bolus and the skin surface, which may result in variability in radiation dose across the target volume. The shape of the canine distal hind extremity is irregular, and commercially available bolus materials do not conform well to this region. The purpose of this study was to assess the dose homogeneity achieved using a petroleum-based bolus material, in combination with a commercially available sheet bolus, for radiation treatment of the canine tarsus. Repeated setups were performed to mimic daily treatment setups in the clinic setting, and computed tomographic scans were performed after each setup. Dose distribution achieved with a cobalt therapy machine and a 6 MV linear accelerator was assessed using three-dimensional treatment planning software. The dose to the clinical target volume fell within 95% and 107% of the prescribed dose for both treatment machines, which is considered clinically acceptable by the authors. This petroleum-based bolus is equivalent to water in its photon attenuation, conforms well to an irregular patient contour, and retains its shape after positioning. Applications to other anatomical sites could be considered.

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