Film dosimetry of megavoltage photon beams: A practical method of isodensity‐to‐isodose curve conversion

Jeffrey F. Williamson, Faiz M. Khan, Subhash C. Sharma

Research output: Contribution to journalLetterpeer-review

124 Scopus citations

Abstract

The central problems of photon beam film dosimetry are the dependence of film response upon photon energy, processing conditions, and film plane orientation. We have overcome these problems by accurately fitting the depth�dependent sensitometric curve of Kodak XV�2 film (exposed parallel to beam axis) to the equation OD(D,d) =ODs(1 − exp {−α0[1+β(d−dm)]D}) where OD(D,d) is the optical density for dose D at depth d. ODs, α0, and β are constants characteristic of the film and beam energy but are independent of field size. Only central axis depth dose data for a single field are required to determine their values. A computer program based upon this equation has been written which successfully generates single field isodose curves from film data for a variety of field sizes (including wedged fields) with an accuracy of ±3%. Data are presented for 60Co, and 4 and 10 MV x rays.

Original languageEnglish
Pages (from-to)94-98
Number of pages5
JournalMedical physics
Volume8
Issue number1
DOIs
StatePublished - Jan 1981

Keywords

  • CALIBRATION
  • COMPUTER CODES
  • FILM DOSIMETRY
  • ISODOSE CURVES
  • OPACITY
  • PHOTON BEAMS
  • X RADIATION

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