title: High dose-per-pulse electron beam dosimetry: Usability and dose-rate independence of EBT3 Gafchromic films.
abstract: OBJECTIVE
  The aim of this study was to assess the suitability of Gafchromic EBT3 films for reference dose measurements in the beam of a prototype high dose-per-pulse linear accelerator (linac), capable of delivering electron beams with a mean dose-rate (Ḋm) ranging from 0.07 to 3000 Gy/s and a dose-rate in pulse (Ḋp) of up to 8 × 106Gy/s. To do this, we evaluated the overall uncertainties in EBT3 film dosimetry as well as the energy and dose-rate dependence of their response.
  
  
  METHODS
  Our dosimetric system was composed of EBT3 Gafchromic films in combination with a flatbed scanner and was calibrated against an ionization chamber traceable to primary standard. All sources of uncertainties in EBT3 dosimetry were carefully analyzed using irradiations at a clinical radiotherapy linac. Energy dependence was investigated with the same machine by acquiring and comparing calibration curves for three different beam energies (4, 8 and 12 MeV), for doses between 0.25 and 30 Gy. Ḋmdependence was studied at the clinical linac by changing the pulse repetition frequency (f) of the beam in order to vary Ḋmbetween 0.55 and 4.40 Gy/min, while Ḋpdependence was probed at the prototype machine for Ḋpranging from 7 × 103to 8 × 106Gy/s. Ḋpdependence was first determined by studying the correlation between the dose measured by films and the charge of electrons measured at the exit of the machine by an induction torus. Furthermore, we compared doses from the films to independently calibrated thermo-luminescent dosimeters (TLD) that have been reported as being dose-rate independent up to such high dose-rates.
  
  
  RESULTS
  We report that uncertainty below 4% (k = 2) can be achieved in the dose range between 3 and 17 Gy. Results also demonstrated that EBT3 films did not display any detectable energy dependence for electron beam energies between 4 and 12 MeV. No Ḋmdependence was found either. In addition, we obtained excellent consistency between films and TLDs over the entire Ḋprange attainable at the prototype linac confirming the absence of any dose-rate dependence within the investigated range (7 × 103to 8 × 106Gy/s). This aspect was further corroborated by the linear relationship between the dose-per-pulse (Dp) measured by films and the charge per pulse (Cp) measured at the prototype linac exit.
  
  
  CONCLUSIONS
  Our study shows that the use of EBT3 Gafchromic films can be extended to reference dosimetry in pulsed electron beams with a very high dose rate. The measurement results are associated with an overall uncertainty below 4% (k = 2) and are dose-rate and energy independent.
authors.affiliation: Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Maud
authors.initials: M
authors.lastname: Jaccard
authors.affiliation: Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Kristoffer
authors.initials: K
authors.lastname: Petersson
authors.affiliation: Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Thierry
authors.initials: T
authors.lastname: Buchillier
authors.affiliation: Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Germond
authors.affiliation: Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Durán
authors.affiliation: Department of Radiation Oncology, Lausanne University Hospital, Lausanne, Switzerland.|Radio-Oncology Laboratory, DO/CHUV, Lausanne University Hospital Lausanne, Lausanne, Switzerland.
authors.forename: Marie-Catherine
authors.initials: MC
authors.lastname: Vozenin
authors.affiliation: Department of Radiation Oncology, Lausanne University Hospital, Lausanne, Switzerland.|Radio-Oncology Laboratory, DO/CHUV, Lausanne University Hospital Lausanne, Lausanne, Switzerland.
authors.forename: Jean
authors.initials: J
authors.lastname: Bourhis
authors.affiliation: Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: François O
authors.initials: FO
authors.lastname: Bochud
authors.affiliation: Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland.
authors.forename: Claude
authors.initials: C
authors.lastname: Bailat
mesh_terms: D004583:Electrons; D005240:Feasibility Studies; D005373:Film Dosimetry / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D010315:Particle Accelerators; D011829:Radiation Dosage
keywords: EBT3 Gafchromic films; dose-rate dependence; energy dependence; high dose-per-pulse; high dose-rate