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

Journal Article · Sun Jun 01 00:00:00 EDT 2014 · Medical Physics

DOI:https://doi.org/10.1118/1.4888741· OSTI ID:22369562

Rossomme, S ^[1]; Renaud, J; Sarfehnia, A; Seuntjens, J ^[2]; Lee, N; Thomas, R ^[3]; Kacperek, A ^[4]; Bertrand, D ^[5]; Vynckier, S ^[1]; Palmans, H ^[3]; MedAustron, Wiener Neustadt ^[6]

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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. Austria

Purpose: To reduce the uncertainty of the beam quality correction factor k_Q,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 k_Q,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 k_Q,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 of 1.2%. k_Q,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 k_Q,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.

• OSTI ID: 22369562
• Journal Information: Medical Physics, Vol. 41, Issue 6; Other Information: (c) 2014 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-2405
• Country of Publication: United States
• Language: English

Related Subjects

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