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For an infinite number of fractions:
Impact of random motion on tumor dose:
- Narrow PTV-margin: cells at PTV edge get
>95% in some fractions, << 95% dose in others (asymmetric)
- Effectively, tumor experiences the planning dose distribution
that is blurred
Blurred dose
Planned (static) dose
Add random errors
M
PTV
= 2.5Σ + 0.7σ