title: Direct absorbed dose to water determination based on water calorimetry in scanning proton beam delivery.
abstract: OBJECTIVE
  The aim of this manuscript is to describe the direct measurement of absolute absorbed dose to water in a scanned proton radiotherapy beam using a water calorimeter primary standard.
  
  
  METHODS
  The McGill water calorimeter, which has been validated in photon and electron beams as well as in HDR 192Ir brachytherapy, was used to measure the absorbed dose to water in double scattering and scanning proton irradiations. The measurements were made at the Massachusetts General Hospital proton radiotherapy facility. The correction factors in water calorimetry were numerically calculated and various parameters affecting their magnitude and uncertainty were studied. The absorbed dose to water was compared to that obtained using an Exradin T1 Chamber based on the IAEA TRS-398 protocol.
  
  
  RESULTS
  The overall 1-sigma uncertainty on absorbed dose to water amounts to 0.4% and 0.6% in scattered and scanned proton water calorimetry, respectively. This compares to an overall uncertainty of 1.9% for currently accepted IAEA TRS-398 reference absorbed dose measurement protocol. The absorbed dose from water calorimetry agrees with the results from TRS-398 well to within 1-sigma uncertainty.
  
  
  CONCLUSIONS
  This work demonstrates that a primary absorbed dose standard based on water calorimetry is feasible in scattered and scanned proton beams.
authors.affiliation: Medical Physics Unit, McGill University, Montréal, Québec, H3G-1A4, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Sarfehnia
authors.forename: B
authors.initials: B
authors.lastname: Clasie
authors.forename: E
authors.initials: E
authors.lastname: Chung
authors.forename: H M
authors.initials: HM
authors.lastname: Lu
authors.forename: J
authors.initials: J
authors.lastname: Flanz
authors.forename: E
authors.initials: E
authors.lastname: Cascio
authors.forename: M
authors.initials: M
authors.lastname: Engelsman
authors.forename: H
authors.initials: H
authors.lastname: Paganetti
authors.forename: J
authors.initials: J
authors.lastname: Seuntjens
mesh_terms: D002151:Calorimetry; D061766:Proton Therapy; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D011879:Radiotherapy Dosage; D013814:Thermal Conductivity; D035501:Uncertainty; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water