Generation and use of measurement-based 3-D dose distributions for 3-D dose calculation verification.

Robin L Stern, B. A. Fraass, A. Gerhardsson, D. L. McShan, K. L. Lam

Research output: Contribution to journalArticle

24 Scopus citations

Abstract

A 3-D radiation therapy treatment planning system calculates dose to an entire volume of points and therefore requires a 3-D distribution of measured dose values for quality assurance and dose calculation verification. To measure such a volumetric distribution with a scanning ion chamber is prohibitively time consuming. A method is presented for the generation of a 3-D grid of dose values based on beam's-eye-view (BEV) film dosimetry. For each field configuration of interest, a set of BEV films at different depths is obtained and digitized, and the optical densities are converted to dose. To reduce inaccuracies associated with film measurement of megavoltage photon depth doses, doses on the different planes are normalized using an ion-chamber measurement of the depth dose. A 3-D grid of dose values is created by interpolation between BEV planes along divergent beam rays. This matrix of measurement-based dose values can then be compared to calculations over the entire volume of interest. This method is demonstrated for three different field configurations. Accuracy of the film-measured dose values is determined by 1-D and 2-D comparisons with ion chamber measurements. Film and ion chamber measurements agree within 2% in the central field regions and within 2.0 mm in the penumbral regions.

Original languageEnglish (US)
Pages (from-to)165-173
Number of pages9
JournalMedical Physics
Volume19
Issue number1
DOIs
StatePublished - Jan 1992
Externally publishedYes

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ASJC Scopus subject areas

  • Biophysics

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