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Medical Physics / Volume 37 / Issue 7 / RADIATION MEASUREMENT PHYSICS

Med. Phys. 37, 3541 (2010); http://dx.doi.org/10.1118/1.3427317 (10 pages)

Direct absorbed dose to water determination based on water calorimetry in scanning proton beam delivery

A. Sarfehnia, E. Chung, and J. Seuntjens

Medical Physics Unit, McGill University, Montréal, Québec, H3G-1A4, Canada

B. Clasie, H. M. Lu, J. Flanz, E. Cascio, M. Engelsman, and H. Paganetti

Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114

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(Received 14 December 2009; accepted 19 April 2010; revised 20 March 2010; published online 15 June 2010)

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Purpose: 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.

© 2010 American Association of Physicists in Medicine

ACKNOWLEDGMENTS

This work has been supported in part by Grant No. RGPIN 298181 of the Natural Sciences and Engineering Research Council of Canada. The assistance of all BPTC technical staff is acknowledged. A.S. is a recipient of a CIHR doctoral fellowship. The water calorimeter in this work was constructed with the help of Robin Van Gils at McGill, while the thermistors were built and provided by David Marchington of Ionizing Radiation Standards division of National Research Council of Canada.

Article Outline

  1. INTRODUCTION
  2. METHODOLOGY
    1. Water calorimeter
    2. Delivery plan
    3. Dose calculation
    4. Heat transport
      1. Conduction and convection
      2. Geometrical considerations
    5. Ionization chamber reference dosimetry
  3. RESULTS AND DISCUSSION
    1. Effects of heat loss by conduction
    2. Uncertainty budget
    3. Absorbed dose
  4. CONCLUSIONS
Digital Object Identifier
http://dx.doi.org/10.1118/1.3427317

KEYWORDS and PACS

Keywords

dosimetry, particle calorimetry, radiation therapy, water calorimetry, primary standard, absolute dosimetry, double scattering, spot scanning, proton radiation, absorbed dose

PACS

  • 87.55.dk

    Dose-volume analysis

  • 87.53.Jw

    Therapeutic applications, including brachytherapy

  • 87.53.Bn

    Dosimetry/exposure assessment

PUBLICATION DATA

ISSN

0094-2405 (print)  

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physicists in Medicine

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