title: An application of GafChromic MD-55 film for 67.5 MeV clinical proton beam dosimetry.
abstract: The purpose of this study is to explore the use of GafChromic MD-55 (RC) film for 67.5 MeV clinical proton beam dosimetry at the Crocker Nuclear Laboratory, University of California, Davis. Several strips of RC film 6 cm x 6 cm in dimension were irradiated at a depth of 18.2 mm corresponding to the middle of a 24 mm spread-out Bragg peak (SOBP). The films were irradiated to a proton dose in the range of 0.5 Gy to 100 Gy. The beam profiles were also measured at the middle of the 24 mm SOBP. The Bragg peak was measured by using a wedge shaped phantom made of Lucite. The Bragg peak measured with RC film was compared with diode and ionization chamber measurements. After background subtraction, the calibration of the dose response of RC film showed, to a maximum deviation of 10%, a linear increase of optical density (OD) with dose from 0.5 to 100 Gy. The uniformity of OD over a single sheet of film showed a variation of +/-6%. The distal-fall off between 90% and 20% measured with GafChromic film for the Bragg peak was 1.3 mm as compared to 1.1 mm for a diode measurement and 1.4 mm for an ionization chamber measurement. The FWHM of the Bragg peak was 7.5 mm when measured with GafChromic film, 5.3 mm when measured with a diode and 8.1 mm as measured by an ionization chamber. The peak/plateau ratio with GafChromic film was 3.3 as compared to 3.7 with a diode and 3.2 with an ionization chamber. In conclusion, GafChromic MD-55 film may be a useful and convenient detector for dose measurement and quality assurance programmes of proton beams.
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco 94143, USA.
authors.forename: I
authors.initials: I
authors.lastname: Daftari
authors.forename: C
authors.initials: C
authors.lastname: Castenadas
authors.forename: P L
authors.initials: PL
authors.lastname: Petti
authors.forename: R P
authors.initials: RP
authors.lastname: Singh
authors.forename: L J
authors.initials: LJ
authors.lastname: Verhey
mesh_terms: D017357:Cyclotrons; D004867:Equipment Design; D019047:Phantoms, Imaging; D019904:Polymethyl Methacrylate; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods*; D012680:Sensitivity and Specificity; D014962:X-Ray Film
chemical_list: D019904:Polymethyl Methacrylate