title: External beam profiles measured with film or ionization chamber.
abstract: Radiation therapy beam profiles measured with an ionization chamber in a scanning water phantom are compared with profiles measured with a standard film dosimetry technique. An 18 cm field was filmed with 4 MV photons in a polystyrene phantom at depths of 1, 7, and 13 cm. The film was scanned with a scanning densitometer and the resulting profiles were converted to dose profiles with a sensitometric curve. To determine the effect of backscatter on the film a special phantom was constructed to eliminate the backscatter from the film measurement. This provided a comparison with the solid film phantom where full backscattering was present. The beam profiles measured with the film differed by less than 3% from the ionization chamber profiles and there was less than 1% difference between the film techniques.
authors.affiliation: Radiation Oncology Department, Johns Hopkins Medical Institute, Baltimore, MD 21205.
authors.forename: M J
authors.initials: MJ
authors.lastname: O'Neill
authors.forename: W C
authors.initials: WC
authors.lastname: Lam
authors.forename: K S
authors.initials: KS
authors.lastname: Lam
authors.forename: M
authors.initials: M
authors.lastname: Partowmah
authors.forename: A
authors.initials: A
authors.lastname: Khalifeh
mesh_terms: D005373:Film Dosimetry; D006801:Humans; D008961:Models, Structural; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy; D012542:Scattering, Radiation; D014867:Water
chemical_list: D014867:Water