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Summary
Basic Dose Calculation Principles
For equal number of MU :
Dose decrease with depth (beyond d
max
)
Dose absorption and inverse square law
Dose increase with larger field sizes
More scatter to contribute to dose (Output factors)
Dose decrease with larger SSD
inverse square law
Dose increase with energy (beyond d
max
)
less attenuation for higher energies
Dose increase off central axis – most at d
max
less at depth.
Flattening filter, Beam spectrum is “softer” off axis
(off axis factors)