Dose Course 2018_Flipping book

Dose per MU formalisms: factor-based dose calculations

Inhomogeneities

Effective depth to a calculation point is the thickness of water equivalent tissue that would attenuate the radiation by the same amount as the actual tissue along a fan-line between the calculation point and the surface

n

 = i 1

If the radiation passes through n different tissues each if thickness d i and density ρ i

d

d

=



eff

i i

Note: TPSs usually report an effective depth for a calculation point, but how exactly this is derived is not always apparent

d