Dose Course 2018_Flipping book

Beam energy spectra - methods to determine spectra for clinical beams

Measurements

Low beam current and/or Compton scatter methods Not practical for clinical use

Monte Carlo methods

Mohan et al MedPhys 12 p 592 1985 widely used for testing BEAM (EGS4/nrc) standard tool Other codes also used, PENELOPE, GEANT, etc. Still not practical for routine use MC data to be standard part of linac purchase procedure?

require trimming of the resulting spectrum so that measured dose matches calculated dose

Analytical modelling from cross sections

Target designs requires use of ‘thick target theory’, i.e. must model the electron transport prior to bremsstrahlung interactions

Unfolding from transmission through attenuators Based on ‘in air’ measurements Requires good control of attenuator purity

Most methods use some support of spectral shape constrains

Unfolding from depth dose distributions in water

Requires access to monoenergetic depth dose data (Monte Carlo) Unfolding methods needs spectral shape constrains

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