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Title: SU-E-T-408: Determination of KQ,Q0-Factors From Water and Graphite Calorimetry in a 60 MeV Proton Beam

Purpose: To reduce the uncertainty of the beam quality correction factor kQ,Q0, for scattered proton beams (SPB). This factor is used in dosimetry protocols, to determine absorbed dose-to-water with ionization chambers. For the Roos plane parallel chambers (RPPICs), the IAEA TRS-398 protocol estimates kQ,Q0-factor to be 1.004(for a beam quality Rres=2 g.cm{sup 2}), with an uncertainty of 2.1%. Methods: A graphite calorimeter (GCal), a water calorimeter (WCal) and RPPICs were exposed, in a single experiment, to a 60 MeV non-modulated SPB. RPPICs were calibrated in terms of absorbed dose-to-water in a 20 MeV electron beam. The calibration coefficient is traceable to NPL's absorbed dose standards. Chamber measurements were corrected for environmental conditions, recombination and polarity. The WCal corrections include heat loss, heat defect and vessel perturbation. The GCal corrections include heat loss and absorbed dose conversion. Except for heat loss correction and its uncertainty in the WCal system, all major corrections were included in the analysis. Other minor corrections, such as beam profile non-uniformity, are still to be evaluated. Experimental kQ,Q0-factors were derived by comparing the results obtained with both calorimeters and ionometry. Results: The absorbed dose-to-water from both calorimeters was found to be within 1.3% with an uncertainty ofmore » 1.2%. kQ,Q0-factor for a RPPIC was found to be 0.998 and 1.011, with a standard uncertainty of 1.4% and 0.9% when the dose is based on the GCal and the WCal, respectively. Conclusion: Results suggest the possibility to determine kQ,Q0-values for PPICs in SPB with a lower uncertainty than specified in the TRS-398 thereby helping to reduce uncertainty on absorbed dose-to-water. The agreement between calorimeters confirms the possibility to use GCal or WCal as primary standard in SPB. Because of the dose conversion, the use of GCal may lead to slightly higher uncertainty, but is, at present, considerably easier to operate.« less
Authors:
 [1] ; ; ;  [2] ; ;  [3] ;  [4] ;  [5] ;  [1] ;  [6] ;  [3] ;  [7]
  1. Universite catholique de Louvain, Brussels (Belgium)
  2. McGill University, Montreal, QC - Canada (Canada)
  3. National Physical Laboratory, Teddington, Middlesex - United Kingdom (United Kingdom)
  4. The Clatterbridge Cancer Centre NHS Foundation, Wirral (United Kingdom)
  5. Ion Beam Applications s.a., Louvain-la-Neuve (Belgium)
  6. (Belgium)
  7. (Austria)
Publication Date:
OSTI Identifier:
22369562
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 41; Journal Issue: 6; Other Information: (c) 2014 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
07 ISOTOPES AND RADIATION SOURCES; 60 APPLIED LIFE SCIENCES; ABSORBED RADIATION DOSES; BEAM PROFILES; CALIBRATION; CALIBRATION STANDARDS; CALORIMETERS; CALORIMETRY; COMPARATIVE EVALUATIONS; CORRECTIONS; DOSIMETRY; ELECTRON BEAMS; GRAPHITE; HEAT; HEAT LOSSES; IAEA; LEAD; MEV RANGE; PERTURBATION THEORY; PROTON BEAMS; RECOMBINATION; WATER