Chapter 6 External Photon Beams: Physical Aspects - IRSN

706.11 SINGLE FIELD ISODOSE DISTRIBUTIONS IN PATIENTS6.11.3 Corrections for tissue inhomogeneities Region (1), point P 1 :The dose is not affected by theinhomogeneity, since the primary beamis not affected and neither is the scattercomponent. Region (2), point P 2 :The dose is mainly affected by changesin the secondary electron fluence and toa lesser extent by changes in theprimary beam attenuation. Region (3), point P 3 :The dose is mainly affected by changesin the primary beam attenuation and lessby changes in scatter.IAEA Radiation Oncology Physics: A Handbook for Teachers and Students - 6.11.3 Slide 3 (139/170)6.11 SINGLE FIELD ISODOSE DISTRIBUTIONS IN PATIENTS6.11.3 Corrections for tissue inhomogeneitiesFour empirical methods have been developed for correctingthe water phantom dose to obtain the dose atpoints P 3 in region (3) beyond the inhomogeneity:• TAR method• Power law TAR method• Equivalent TAR method• Isodose shift methodIAEA Radiation Oncology Physics: A Handbook for Teachers and Students - 6.11.3 Slide 4 (140/170)