07 - Treatment Planning I - Isodose Distributions

07 - Treatment Planning I - Isodose Distributions - Lecture...

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1 Treatment Planning I: Isodose Distributions Tarun K. Podder, PhD, DABR Department of Radiation Oncology Brody School of Medicine Leo Jenkins Cancer Center East Carolina University February 01, 2011 Lecture # 7 (Ch. 11)
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2 Isodose Distribution Parameters
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3 Isodose Distribution Isodose curve – line passing through points of equal dose. Isodose chart – a family of isodose curves usually drawn at equal increments of PDD.
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4 Isodose Distribution Parameters
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5 Isodose Distribution SSD Technique Isocentric Technique
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6 Isodose Chart SSD SAD
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7
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8 Field Size 100% 90% 50% 30%
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9
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10 Beam Quality and Isodose Distribution 200 kVp 60 Co 4 MV 10 MV
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11
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Wedge Filter Isodose curves for a wedge filter. A: Normalized to Dmax. B: normalized to D max , without the wedge. 60 Co, wedge angle = 45 degrees, field size = 8 × 10 cm, source to surface distance = 80 cm.
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13 Wedge Angle Wedge angle refers the complement of the angle at which the isodose line is tilted in relation to the central axis, for a given depth This depth is normally defines as 10 cm (ICRU 24)
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14 Wedge Angle ( θ ) Location of wedge tray in Linac (Varian/ Siemens)
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15
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16 Wedge Filter Individualized wedge – for a specific field width in which the thin end of the wedge is always aligned with the field border. Universal wedge – the center of the wedge is fixed at the beam axis and the field can be oppened to any width. Dynamic wedging – accomplished by having an independently moving collimator leaf move across the field during treatment. The speed at which the MLC moves will determine the angle of the sloping isodose curve.
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17 Design of Wedge Filter Text
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18 Combination of Radiation Fields - pair of parallel opposed fields photon beam photon beam photon beam photon beam Isocentric plan: each beam is weighted 100 at the isocenter, i.e. 100 cGy at isocenter.
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07 - Treatment Planning I - Isodose Distributions - Lecture...

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