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KMID : 0352819860020010113
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Kosin Medical Journal
1986 Volume.2 No. 1 p.113 ~ p.122
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The Field Size Effect on Electron Beam Depth Dose and Output Factors
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Abstract
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Linac 18 medical linear accelerator produces electron beams of 6, 9, 12, 15, and 18 MeV. We measured electron beam depth dose and output factors for various fields using an ionization chamber. The electron fields were 5, 7, 10, 12, 15, and 20cm squares.
Several features common to all beam energies can be observed as the area of the treatment field becomes smaller. They are (1) the depth of maximum dose(d,,,.) shift towards the surface, (2) the depth of the 80% isodose line becomes smaller, (3) the fall-off region of the curve becomes less steep, (4) the practical range of the beam(Rp) remains constant.
Electron beam output factors as a function of field size are shown in the graphs and the tables generated from these measurements.
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