Dose Course 2018_Flipping book
7
How to get the dose distribution?
❑ To get a depth dependence one has to correct the planar fluence of electrons
D ( r , z ) = d p
( r , z ) × g ( z )
❑ The weighting factor g ( z ) is determined such that the dose as a function of depth on the central axis for a given field size exactly equals the measured central axis depth dose o Corrected to infinite SSD o Bremsstrahlung dose, is subtracted (assumed constant at all depths less than R p
D measured , electrons _ only , SSD =¥
(0,0, z )
❑ In practice, g ( z ) must be determined for a range of field sizes for a beam of a particular energy as the model can only predict the change over a small range of field sizes
From Handbook of Radiotherapy Physics Ed Mayles, Nahum and Rosenwald
Dublin 2018
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