Dosimetry for IMRT

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Monitor Backscatter for Square On On-Axis Axis Fields Varian 2100 – 10 MV Liu et al., Med. Phys 2000;27:737-744
Conclusion • IMRT uses complex field boundaries and many small fields to achieve more conformal dose distributions. • Partial volume effects can result in severe error especially when measuring the dose in high gradients. • A new method for determining the effect of field obscuring g is pproposed p to eliminate ppartial volume effects. • IMRT deliveries are far from the measurement conditions of calibration. • IAEA has developed a formalism to account for small and novel beams. • Independent calculations or measurements for patient patientspecific QA are required for IMRT. • IAEA will recommend that 85% of measurement values (dose or distance to agreement) are within 5%. • Model-based monitor unit calculations are simple but should include scatter into monitor chamber.
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Dosimetry for IMRT Thomas Rockwell
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Outline • Dosimetry Issues Releva
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Non-Uniform Intensity Changes the E
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Signal (fC) 12000 10000 8000 6000 4
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Outpuut Factorr 0.9 0.8 00.7 0.6 05
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High Uncertainty in Output Factors
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Problems with Conventional Output F
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Animation of Scanning Path From the
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Animation of Scanning Path From the
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Dose D Ratio Dosse Impact of Source
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No Difference Between Water and Sol
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Small Vs. Farmer Chambers A1SL: 0.0
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The Same Technique Could Be Applied
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Measurements Would Benchmark Source
Page 30 and 31: Audit for TRS 398 Reference Dosimet
Page 32 and 33: IMRT Is About Using Small Fields In
Page 34 and 35: Meeting for the Dosimetry Code of P
Page 38 and 39: Examples of Small and Novel Fields
Page 40 and 41: Calculate Using MC Using method of
Page 42 and 43: Dose Calibration Correction Factor
Page 44 and 45: “Effective kQ” for Tomo 1. Dete
Page 46 and 47: ICRU Committee on IMRT Sponsors •
Page 48 and 49: QA for IMRT • Appropriate QQA of
Page 50 and 51: 1 mm Bands Leaf Positioning Errors
Page 52 and 53: Radiation Field Edge Offset 0.7mm o
Page 54 and 55: Dynamic Multileaf Collimator MLC (D
Page 56 and 57: TomoTherapy py Leaf Latencyy • To
Page 58 and 59: End-to-End QA
Page 60 and 61: Dose (GGy) On and Off-Axis Results
Page 62 and 63: Delivery QA Panel
Page 64 and 65: NNote t th the High Gradients Compa
Page 66 and 67: Independent Calculation
Page 68 and 69: Gamma Function � ( r , r ) �{[
Page 70 and 71: Molineu et al IJROBP 2005 Ibott et
Page 72 and 73: Dm/Dc 1.2 1.15 1.1 1.05 1 0.95 0.9
Page 74 and 75: Frequency Inter-Institution Dose Ac
Page 76 and 77: QA Accuracy y for IMRT • Previous
Page 78 and 79: Monitor Units Calculations for MMod
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Dosimetry for IMRT

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