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Ceberg

Crister Ceberg

Professor

Ceberg

Tissue-phantom ratios from percentage depth doses

Författare

  • Bengt E Bjärngard
  • Timothy C Zhu
  • Crister Ceberg

Summary, in English

When converting fractional (percentage) depth doses to tissue-phantom ratios, one must use a factor that accounts for the different source-to-point distances. Two minor correction factors are also involved. One is the ratio of total to primary dose at the two different distances from the source, for the same depth and field size. This factor is usually ignored. It was determined experimentally that this can introduce up to 1.5% error at 6 MV. The second correction factor reflects differences related to scattered photons and electrons at the depth of normalization in the two geometries. This correction is accounted for in published conversion procedures. It was found to be less than 1% provided the normalization depth is sufficient for electron equilibrium, which occurs first well beyond the depth of maximum dose. One may avoid electron-equilibrium problems by using an interim normalization depth that provides electron equilibrium with some margin, renormalizing to a shallower depth if desired. With this precaution, the accuracy when measured fractional depth doses were converted to tissue-phantom ratios was comparable to that of directly measured tissue-phantom ratios even when the correction factors were ignored.

Avdelning/ar

  • Medicinsk strålningsfysik, Lund

Publiceringsår

1996

Språk

Engelska

Sidor

629-634

Publikation/Tidskrift/Serie

Medical Physics

Volym

23

Issue

5

Dokumenttyp

Artikel i tidskrift

Förlag

American Association of Physicists in Medicine

Ämne

  • Biophysics

Status

Published

ISBN/ISSN/Övrigt

  • ISSN: 0094-2405