title: Dosimetric verification of compensated beams using radiographic film.
abstract: BACKGROUND
  External photon beam modulation using compensators in order to achieve a desired dose distribution when brachytherapy treatment is followed by external beam radiation is a well-established technique. A compensator modulates the central part of the beam, and the dose beneath the thickest part of the compensator is delivered mostly by scattered, low energy photons. A two-dimensional detector with a good spatial resolution is needed for the verification of those beams. In this work, the influence of different types of detectors on the measured modulated dose distributions was examined.
  
  
  METHODS
  Dosimetric verification was performed using X-Omat V, Eastman Kodak radiographic films at different depths in a solid water phantom. The film measurements were compared with those made by ionization chambers. Photon beams were also modelled using EGSnrc Monte Carlo algorithm to explain the measured results.
  
  
  RESULTS
  Monte Carlo calculated over-response of the film under the thickest part of the compensator was over 15%, which was confirmed by measurements. The magnitude of over-response could be associated with changes in the spectra of photon energy in the beam.
  
  
  CONCLUSIONS
  The radiographic film can be used for the dosimetry of compensated high energy photon beams, with limitations in volumes where photon spectra are hardly degraded.
authors.affiliation: University Hospital Rijeka, Radiotherapy Department, Physics Division, Rijeka, Croatia.
authors.forename: Slaven
authors.initials: S
authors.lastname: Jurkovic
authors.forename: Gordana
authors.initials: G
authors.lastname: Zauhar
authors.forename: Dario
authors.initials: D
authors.lastname: Faj
authors.forename: Deni Smilovic
authors.initials: DS
authors.lastname: Radojcic
authors.forename: Manda
authors.initials: M
authors.lastname: Svabic
authors.forename: Mladen
authors.initials: M
authors.lastname: Kasabasic
authors.forename: Ana
authors.initials: A
authors.lastname: Diklic