Out of Field Dose Reduction by Geoffrey Ibbott, PhD

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Neutrons• Neutrons produced by photons striking theprimary collimator, jaws, and target.• Neutrons are important because of theirhigh (uncertain) RBE.Radiation Type Energy Quality FactorX and gamma Rays All 1Neutrons< 10 keV 510 keV to 100 keV 10100 keV to 2 MeV 202 MeV to 20 MeV 10> 20 MeV 5
Calculations of Risk withEarly IMRT TechniquesLikelihood of Secondary Fatal Malignancy (%)Technique 6 MV 18 MV 25 MVConventional 0.3 1.8 3MLCmodulat ed1.0 5.1 8.4SerialTomotherapy2.7 14.9 24.4Calculated risk estimatesFollowill et al (1997)
Page 1 and 2: Appropriate Planning inRadiation On
Page 3: Secondary Cancer Risk in Radiation
Page 7 and 8: Dose Levels in RT Patients (3D CRT
Page 9 and 10: Two Ways to Determine Absorbed Dose
Page 11 and 12: 3D VIP-Man Model fromthe Visible Hu
Page 13 and 14: Comparison of Calculated and Measur
Page 15 and 16: Results: Total (Photon + Neutron) O
Page 17 and 18: Monte-Carlo Calculations: Summary
Page 19 and 20: Most Recent Measurements• Anthrop
Page 21 and 22: Pediatric Procedures• Pediatric C
Page 23 and 24: Neutron Measurements• Neutron flu
Page 25 and 26: Neutron Measurement Cautions• Gol
Page 27 and 28: Risk (%) of Secondary Cancer perCom
Page 29 and 30: Dose Equivalent and Risk (%) perCom
Page 31 and 32: How significant can this be?Stray R
Page 33 and 34: Comparison of the doses in the pedi
Page 35 and 36: Take Home Message• Biggest uncert

Out of Field Dose Reduction by Geoffrey Ibbott, PhD

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