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IMRT – Why?
The biological argument, dose escalation
3
ESTRO physics course 2017
Probability of
Tumor Control
Probability of
Normal Tissue
Damage
Therapeutic
Effect (A)
Target Dose (Gy)
1.0
0
A B
Therapeutic
Effect (B)
MAX. TOXICITY LEVEL
Respons
“Increased conformity
keeps high dose levels
away from OAR”
IMRT – Why? Looking at conformity
“Conformity index” is a
measure of how well
confined to the target
volume:
CI=
V
target
/
V
treated
Conventional RT gives a
low CI whereas the CI
of IMRT approached
unity.
4
Conventional Radiotherapy
Intensity Modulated Radiotherapy
Knoos T, Kristensen I, Nilsson P:
Volumetric and dosimetric evaluation of radiation treatment plans: radiation conformity index.
Int J Radiat Oncol Biol Phys 1998, 42(5):1169-1176