title: High dose per fraction dosimetry of small fields with gafchromic EBT2 film.
abstract: OBJECTIVE
  Small field dosimetry is prone to uncertainties due to the lack of electronic equilibrium and the use of the correct detector size relative to the field size measured. It also exhibits higher sensitivity to setup errors as well as large variation in output with field size and shape. Radiochromic film is an attractive method for reference dosimetry in small fields due to its ability to provide 2D dose measurements while having minimal impact on the dose distribution. Gafchromic EBT2 has a dose range of up to 40 Gy; therefore, it could potentially be useful for high dose reference dosimetry with high spatial resolution. This is a requirement in stereotactic radiosurgery deliveries, which deliver high doses per fraction to small targets.
  
  
  METHODS
  Targets of 4 mm and 12 mm diameters were treated to a minimum peripheral dose of 21 Gy prescribed to 80% of the maximum dose in one fraction. Target doses were measured with EBT2 film (both targets) and an ion chamber (12 mm target only). Measured doses were compared with planned dose distributions using profiles through the target and minimum peripheral dose coverage.
  
  
  RESULTS
  The measured target doses and isodose coverage agreed with the planned dose within +/-1 standard deviation of three measurements, which were 2.13% and 2.5% for the 4 mm and 12 mm targets, respectively.
  
  
  CONCLUSIONS
  EBT2 film is a feasible dosimeter for high dose per fraction reference 2D dosimetry.
authors.affiliation: Department of Human Oncology, University of Wisconsin-Madison, Madison, Wisconsin 53792, USA.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Hardcastle
authors.forename: Amar
authors.initials: A
authors.lastname: Basavatia
authors.forename: Adam
authors.initials: A
authors.lastname: Bayliss
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Tomé
mesh_terms: D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005373:Film Dosimetry / Q000295:instrumentation*; D011829:Radiation Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014962:X-Ray Film