title: Measurement of gold nanofilm dose enhancement using unlaminated radiochromic film.
abstract: OBJECTIVE
  Bombarding high-Z material with x-ray radiation releases Auger electrons and Coster-Kronig electrons, along with deeper penetrating fluorescent x-rays and photoelectrons. The Auger and Coster-Kronig electron penetration distance is on the order of nanometers to micrometers in water or tissue, creating a large dose enhancement accompanied by a RBE greater than 1 at the cellular level. The authors' aim is to measure the gold nanofilm dose enhancement factor (DEF) at the cellular level with unlaminated radiochromic film via primary 50 kVp tungsten x-ray spectrum interaction, similar to an electronic brachytherapy spectrum.
  
  
  METHODS
  Unlaminated Gafchromic(®) EBT2 film and Monte Carlo modeling were combined to derive DEF models. Gold film of thickness 23.1 ±  4.3 nm and surface roughness of 1.2 ± 0.2 nm was placed in contact with unlaminated radiochromic film in a downstream orientation and exposed to a 50 kVp tungsten bremsstrahlung, mean energy 19.2 keV. Film response correction factors were derived by Monte Carlo modeling of electron energy deposition in the film's active layer, and by measuring film energy dependence from 4.5 keV to 50 kVp.
  
  
  RESULTS
  The measured DEF within a 13.6 μm thick water layer was 0.29 with a mean dose of 94 ± 9.4 cGy from Au emissions and 324 ± 32.4 cGy from the 50 kVp primary beam. Monte Carlo derived correction factors allowed determination of Au contributed dose in shallower depths at 0.25 μm intervals. Maximum DEF of 18.31 was found in the first 0.25 μm water depth.
  
  
  CONCLUSIONS
  Dose enhancement from Au nanofilm can be measured at the cellular level using unlaminated radiochromic film. Complementing the measured dose value with Monte Carlo calculations allows estimation of dose enhancement at depth increments within the cellular range.
authors.affiliation: Department of Radiation Oncology, School of Medicine, Wayne State University, Detroit, Michigan 48201.
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Rakowski
authors.affiliation: Department of Physics, Wayne State University, Detroit, Michigan 48201.
authors.forename: Suvra S
authors.initials: SS
authors.lastname: Laha
authors.affiliation: Department of Radiation Oncology, School of Medicine, Wayne State University, Detroit, Michigan 48201.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Snyder
authors.affiliation: Department of Radiation Oncology, School of Medicine, Wayne State University, Detroit, Michigan 48201 and MidMichigan Health, Midland, Michigan 48670.
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Buczek
authors.affiliation: Department of Radiation Oncology, School of Medicine, Wayne State University, Detroit, Michigan 48201 and Missouri Cancer Associates, Columbia, Missouri 65202.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Tucker
authors.affiliation: Department of Chemical Engineering and Materials Science, College of Engineering, Wayne State University, Detroit, Michigan 48201.
authors.forename: Fangchao
authors.initials: F
authors.lastname: Liu
authors.affiliation: Department of Chemical Engineering and Materials Science, College of Engineering, Wayne State University, Detroit, Michigan 48201.
authors.forename: Guangzhao
authors.initials: G
authors.lastname: Mao
authors.affiliation: Department of Radiation Oncology, School of Medicine, Wayne State University, Detroit, Michigan 48201.
authors.forename: Yair
authors.initials: Y
authors.lastname: Hillman
authors.affiliation: Department of Physics, Wayne State University, Detroit, Michigan 48201.
authors.forename: Gavin
authors.initials: G
authors.lastname: Lawes
mesh_terms: D002138:Calibration; D005373:Film Dosimetry / Q000379:methods*; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles; D009010:Monte Carlo Method
chemical_list: D006046:Gold