Dosimetry of a small air cavity for clinical electron beams: A Monte Carlo study

Medical Dosimetry : Official Journal of the American Association of Medical Dosimetrists
James C L Chow, Grigor N Grigorov

Abstract

This study investigated dosimetric changes in a water phantom when a small air cavity was presented at the central axis of a clinical electron beam. We used 6-, 9-, and 16-MeV electron beams with a 10 x 10 cm(2) applicator and cutout produced by a Varian 21 EX linear accelerator. Percentage depth doses (PDDs) for different depths (0.5-7 cm), thicknesses (2-10 mm), and widths (1-5 cm) of air cavities were calculated using Monte Carlo simulations (EGSnrc code) validated by film measurements. By comparing PDDs of phantoms with and without the air cavity, it was found that when the depth or thickness of cavity was changed, the PDD curve below the cavity was shifted with a distance equal to the thickness of the cavity. However, when the width of the air cavity was changed, both the PDD curve and its slope within and below the cavity were changed. A larger width of the air cavity resulted in a shallower PDD curve within the cavity. The slope of the PDD curve below the cavity tended towards a value as the width of the air cavity was increased to 3-5 cm for the 6-, 9-, and 16-MeV electron beams. The dependence of the depth dose on the width of the air cavity is a result of the contribution of the electron side scattering in the water s...Continue Reading

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Citations

Aug 8, 2013·Physica Medica : PM : an International Journal Devoted to the Applications of Physics to Medicine and Biology : Official Journal of the Italian Association of Biomedical Physics (AIFB)·M Zarza-MorenoG Mora

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