A new approach to CT pixel based photon dose calculations in heterogeneous media

John W. Wong, R. Mark Henkelman

Research output: Contribution to journalArticlepeer-review

45 Scopus citations


The effects of small cavities on dose in water and the dose in a homogeneous nonunit density medium illustrate that inhomogeneities do not act independently in photon dose perturbation, and serve as two constraints which should be satisfied by approximate methods of computed tomography (CT) pixel based dose calculations. Current methods at best satisfy only one of the two constraints and show inadequacies in some intermediate geometries. We have developed an approximate method that satisfies both these constraints and treats much of the synergistic effect of multiple inhomogeneities correctly. The method calculates primary and first scatter doses by first order ray tracing with the first scatter contribution augmented by a component of second scatter that behaves like first scatter. Multiple scatter dose perturbation values extracted from small cavity experiments are used in a function which approximates the small residual multiple scatter dose. For a wide range of geometries tested, our method agrees very well with measurements. The average deviation is less than 2% with a maximum of 3%. In comparison, calculations based on existing methods can have errors larger than 10%.

Original languageEnglish (US)
Pages (from-to)199-208
Number of pages10
JournalMedical physics
Issue number2
StatePublished - Mar 1983
Externally publishedYes


  • cat scanning
  • cavities
  • compton effect
  • computerized tomography
  • dose response relationships
  • geometry
  • multiple scattering
  • phantoms
  • photon transport
  • radiation doses
  • scattering
  • spatial dose distributions
  • water
  • x ray dosimetry

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging


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