Dose Course 2018_Flipping book

What’s the fuzz about dose to medium or dose to water? Macro and micro targets!

Issues

Macro scale: localized targets, geometrically formalized as GTV,CTV,ITV and PTV OAR identified for avoidance elemental compositions and densities assigned as averages over cm 3 scale Micro scale: the cell nucleus DNA is the primary site of radiation damage cell diameter varies 5-100 m m cell nucleus diameter 2-10 m m, DNA double helix 2 nm

elemental compositions and densities can vary a lot over nm to m m scales cavity theory can be used for dose ratios over short range media variations

The fuzz:

is water a good standard surrogate medium for cell nucleus? “wrong” cavity theory often used, depends on cavity size and radiation quality cell nucleus size confused with voxel size and/or detector size some common scaling “standards” proved to yield non-expected results no formalized recommendations to follow

A relief:

for MV photons large differences only occur for cell nuclei embedded in bone

From Anders Ahnesjö