title: Development and application of a water calorimeter for the absolute dosimetry of short-range particle beams.
abstract: In this work, we describe a new design of water calorimeter built to measure absorbed dose in non-standard radiation fields with reference depths in the range of 6-20 mm, and its initial testing in clinical electron and proton beams. A functioning calorimeter prototype with a total water equivalent thickness of less than 30 mm was constructed in-house and used to obtain measurements in clinical accelerator-based 6 MeV and 8 MeV electron beams and cyclotron-based 60 MeV monoenergetic and modulated proton beams. Corrections for the conductive heat transfer due to dose gradients and non-water materials was also accounted for using a commercial finite element method software package. Absorbed dose to water was measured with an associated type A standard uncertainty of approximately 0.4% and 0.2% for the electron and proton beam experiments, respectively. In terms of thermal stability, drifts were on the order of a couple of hundred µK min-1, with a short-term variation of 5-10 µK. Heat transfer correction factors ranged between 1.021 and 1.049. The overall combined standard uncertainty on the absorbed dose to water was estimated to be 0.6% for the 6 MeV and 8 MeV electron beams, as well as for the 60 MeV monoenergetic protons, and 0.7% for the modulated 60 MeV proton beam. This study establishes the feasibility of developing an absorbed dose transfer standard for short-range clinical electrons and protons and forms the basis for a transportable dose standard for direct calibration of ionization chambers in the user's beam. The largest contributions to the combined standard uncertainty were the positioning (⩽0.5%) and the correction due to conductive heat transfer (⩽0.4%). This is the first time that water calorimetry has been used in such a low energy proton beam.
authors.affiliation: Medical Physics Unit, McGill University, Montréal, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Renaud
authors.forename: S
authors.initials: S
authors.lastname: Rossomme
authors.forename: A
authors.initials: A
authors.lastname: Sarfehnia
authors.forename: S
authors.initials: S
authors.lastname: Vynckier
authors.forename: H
authors.initials: H
authors.lastname: Palmans
authors.forename: A
authors.initials: A
authors.lastname: Kacperek
authors.forename: J
authors.initials: J
authors.lastname: Seuntjens
mesh_terms: D002138:Calibration; D002151:Calorimetry / Q000379:methods*; D017357:Cyclotrons / Q000295:instrumentation*; D004583:Electrons; D011522:Protons; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D013814:Thermal Conductivity; D014867:Water / Q000737:chemistry*
chemical_list: D011522:Protons; D014867:Water