Dosimetric Characteristics of Clinical Photon Beams

Is depth ionization data depth dose?
YES!!!
With the caveat,
�� TCPE exists at the point of measurement
measurement.
� the energy spectrum of incident photons does not change with the
depth.
�� fluence across the detector remains the same same.
These conditions are met at depths beyond the range of
contaminant charged particles
However at shallow depth, The contaminants and
secondary electrons have energy spectra that change
rapidly with depth.
� Results in a variation of ~10% in restricted mass stopping power
ratio data for water and air.
�Translates into a spatial uncertainty of less than 1.5 mm in dose in the
build up region