Chapter 6 External Photon Beams: Physical Aspects - IRSN

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566.9 OFF-AXIS RATIOS AND BEAM PROFILES6.9.2 Beam symmetry S is calculated fromS= 100 area left area rightarea left+ area rightand should be less than 2%.Practical options for determination of areas under theprofile curve with a hard copy of the profile are:• Using a planimeteror• Counting squares on graph paper.IAEA Radiation Oncology Physics: A Handbook for Teachers and Students - 6.9.2 Slide 2 (111/170)6.9 OFF-AXIS RATIOS AND BEAM PROFILES6.9.2 Beam symmetryThe areas under thez max profile can oftenbe determined usingan automatic softwareoption on the watertank scanning device(3-D isodose plotter).S= 100 area left area rightarea left+ area rightIAEA Radiation Oncology Physics: A Handbook for Teachers and Students - 6.9.2 Slide 3 (112/170)
576.10 ISODOSE DISTRIBUTIONS IN WATER PHANTOMS<strong>Physical</strong> characteristics of radiation beams are usuallymeasured in phantoms under standard conditions:• Homogeneous, unit density phantom• Flat phantom surface• Perpendicular beam incidenceCentral axis depth dose data in conjunction with doseprofiles contain complete 2-D and 3-D information aboutthe radiation beam.IAEA Radiation Oncology Physics: A Handbook for Teachers and Students - 6.10 Slide 1 (113/170)6.10 ISODOSE DISTRIBUTIONS IN WATER PHANTOMSPlanar and volumetric dose distributions are usuallydisplayed with isodose curves and isodose surfaces,which connect points of equal dose in a volume ofinterest.The isodose curves and surfaces are usually drawn atregular intervals of absorbed dose and are expressedas a percentage of the dose at a specific referencepoint.IAEA Radiation Oncology Physics: A Handbook for Teachers and Students - 6.10 Slide 2 (114/170)
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26.1 INTRODUCTIONRadiotherapy (also
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46.2 QUANTITIES USED IN DESCRIBING
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Page 12 and 13: 126.4 INVERSE SQUARE LAW We assume
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Chapter 6 External Photon Beams: Physical Aspects - IRSN

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