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