Skip to main content
banner image
No data available.
Please log in to see this content.
You have no subscription access to this content.
No metrics data to plot.
The attempt to load metrics for this article has failed.
The attempt to plot a graph for these metrics has failed.
The full text of this article is not currently available.
/content/aapm/journal/medphys/37/11/10.1118/1.3495537
1.
1.P. R. Almond, P. J. Biggs, B. M. Coursey, W. F. Hanson, M. S. Huq, R. Nath, and D. W. O. Rogers, “AAPM’s TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams,” Med. Phys. 26, 18471870 (1999).
http://dx.doi.org/10.1118/1.598691
2.
2.IAEA, “Absorbed dose determination in external beam radiotherapy: An international code of practice for dosimetry based on standards of absorbed dose to water, IAEA Technical Report Series No. 398 (IAEA, Vienna, 2001).
3.
3.L. A. Buckley and D. W. O. Rogers, “Wall correction factors, , for thimble ionization chambers,” Med. Phys. 33, 455464 (2006).
http://dx.doi.org/10.1118/1.2161403
4.
4.J. Wulff, J. T. Heverhagen, and K. Zink, “Monte-Carlo-based perturbation and beam quality correction factors for thimble ionization chambers in high-energy photon beams,” Phys. Med. Biol. 53, 28232836 (2008).
http://dx.doi.org/10.1088/0031-9155/53/11/005
5.
5.L. L. W. Wang and D. W. O. Rogers, “The replacement correction factors for cylindrical chambers in high-energy photon beams,” Phys. Med. Biol. 54, 16091620 (2009).
http://dx.doi.org/10.1088/0031-9155/54/6/014
6.
6.D. M. González-Castaño, G. H. Hartmann, F. Sanchez-Doblado, F. Gomez, R. -P. Kapsch, J. Pena, and R. Capote, “The determination of beam quality correction factors: Monte Carlo simulations and measurements,” Phys. Med. Biol. 54, 47234741 (2009).
http://dx.doi.org/10.1088/0031-9155/54/15/006
7.
7.L. Tantot and J. P. Seuntjens, “Modeling ionization chamber response to nonstandard beam configurations,” J. Phys. Conf. Ser. 102, 012013 (2008).
http://dx.doi.org/10.1088/1742-6596/102/1/012023
8.
8.J. P. Seuntjens, C. K. Ross, K. R. Shortt, and D. W. O. Rogers, “Absorbed-dose beam quality conversion factors for cylindrical chambers in high-energy photon beams,” Med. Phys. 27, 27632779 (2000).
http://dx.doi.org/10.1118/1.1328081
9.
9.A. Krauss and R. -P. Kapsch, “Calorimetric determination of factors for NE 2561 and NE 2571 ionization chambers in and radiotherapy beams of 8 MV and 16 MV photons,” Phys. Med. Biol. 52, 62436259 (2007).
http://dx.doi.org/10.1088/0031-9155/52/20/011
10.
10.H. Palmans, W. Mondelaers, and H. Thierens, “Absorbed dose beam quality correction factors for the NE2571 chamber in a 5 MV and 10 MV photon beam,” Phys. Med. Biol. 44, 647663 (1999).
http://dx.doi.org/10.1088/0031-9155/44/3/002
11.
11.I. Kawrakow and D. W. O. Rogers, “The EGSnrc code system: Monte Carlo simulation of electron and photon transport,” NRC Technical Report No. PIRS-701, v4-2-2-5 (National Research Council of Canada, Ottawa, Canada, 2007). See http://www.irs.inms.nrc.ca/inms/irs/EGSnrc/EGSnrc.html.
12.
12.I. Kawrakow, “Accurate condensed history Monte Carlo simulation of electron transport. I. EGSnrc, the new EGS4 version,” Med. Phys. 27, 485498 (2000).
http://dx.doi.org/10.1118/1.598917
13.
13.J. Wulff, K. Zink, and I. Kawrakow, “Efficiency improvements for ion chamber calculations in high energy photon beams,” Med. Phys. 35, 13281336 (2008).
http://dx.doi.org/10.1118/1.2874554
14.
14.I. Kawrakow, “egspp: The EGSnrc C++ class library,” Technical Report No. PIRS-899 (National Research Council of Canada, Ottawa, Canada, 2005).
15.
15.E. G. A. Aird and F. T. Farmer, “The design of a thimble chamber for the Farmer dosemeter,” Phys. Med. Biol. 17, 169174 (1972).
http://dx.doi.org/10.1088/0031-9155/17/2/001
16.
16.D. J. La Russa, M. McEwen, and D. W. O. Rogers, “An experimental and computational investigation of the standard temperature-pressure correction factor for ion chambers in kilovoltage x rays,” Med. Phys. 34, 46904699 (2007).
http://dx.doi.org/10.1118/1.2799580
17.
17.D. W. O. Rogers, in Clinical Dosimetry Measurements in Radiotherapy, edited by D. W. O. Rogers and J. E. Cygler (Medical Physics, Madison, 2009), pp. 239296.
18.
18.G. Mora, A. Maio, and D. W. O. Rogers, “Monte Carlo simulation of a typical therapy source,” Med. Phys. 26, 24942502 (1999).
http://dx.doi.org/10.1118/1.598770
19.
19.D. Sheikh-Bagheri and D. W. O. Rogers, “Monte Carlo calculation of nine megavoltage photon beam spectra using the BEAM code,” Med. Phys. 29, 391402 (2002).
http://dx.doi.org/10.1118/1.1445413
20.
20.R. Mohan, C. Chui, and L. Lidofsky, “Energy and angular distributions of photons from medical linear accelerators,” Med. Phys. 12, 592597 (1985).
http://dx.doi.org/10.1118/1.595680
21.
21.D. W. O. Rogers, B. Walters, and I. Kawrakow, “BEAMnrc users manual,” NRC Report No. PIRS 509(a), Rev. K, 2006.
22.
22.N. I. Kalach and D. W. O. Rogers, “Which accelerator photon beams are ‘clinic-like’ for reference dosimetry purposes?,” Med. Phys. 30, 15461555 (2003).
http://dx.doi.org/10.1118/1.1573205
23.
23.J. H. Hubbell, “Review of photon interaction cross section data in the medical and biological context,” Phys. Med. Biol. 44, R1R22 (1999).
http://dx.doi.org/10.1088/0031-9155/44/1/001
24.
24.M. J. Berger, J. H. Hubbell, S. M. Seltzer, J. S. Coursey, and D. S. Zucker, “XCOM: Photon cross section database (version 1.2),” NIST Report No. NBSIR 87-3597 (NIST, Gaithersburg, MD, 1999). See http://physics.nist.gov/xcom.
25.
25.M. G. Mitch, L. A. DeWerd, R. Minniti, and J. F. Williamson, in Clinical Dosimetry Measurements in Radiotherapy, edited by D. W. O. Rogers and J. E. Cygler (Medical Physics, Madison, 2009), pp. 723757.
26.
26.ICRU, “Stopping powers for electrons and positrons,” ICRU Report No. 37 (ICRU, Bethesda, MD, 1984).
27.
27.D. W. O. Rogers and I. Kawrakow, “Monte Carlo calculated correction factors for primary standards of air-kerma,” Med. Phys. 30, 521543 (2003).
http://dx.doi.org/10.1118/1.1563663
28.
28.J. Wulff, J. T. Heverhagen, K. Zink, and I. Kawrakow, “Investigation of systematic uncertainties in Monte Carlo-calculated beam quality correction factors,” Phys. Med. Biol. 55, 44814493 (2010).
http://dx.doi.org/10.1088/0031-9155/55/16/S04
29.
29.L. A. Buckley, I. Kawrakow, and D. W. O. Rogers, “CSnrc: Correlated sampling Monte Carlo calculations using EGSnrc,” Med. Phys. 31, 34253435 (2004).
http://dx.doi.org/10.1118/1.1813891
30.
30.I. Kawrakow, “Accurate condensed history Monte Carlo simulation of electron transport. II. Application to ion chamber response simulations,” Med. Phys. 27, 499513 (2000).
http://dx.doi.org/10.1118/1.598918
31.
31.H. Svensson and A. Brahme, in Radiation Dosimetry, edited by C. G. Orton (Plenum, New York, 1986), pp. 87170.
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/37/11/10.1118/1.3495537
Loading
/content/aapm/journal/medphys/37/11/10.1118/1.3495537
Loading

Data & Media loading...

Loading

Article metrics loading...

/content/aapm/journal/medphys/37/11/10.1118/1.3495537
2010-10-27
2016-06-29

Abstract

Purpose:

To use EGSnrc Monte Carlo simulations to directly calculate beam quality conversion factors,, for 32 cylindrical ionization chambers over a range of beam qualities and to quantify the effect of systematic uncertainties on Monte Carlo calculations of . These factors are required to use the TG-51 or TRS-398 clinical dosimetry protocols for calibrating external radiotherapy beams.

Methods:

Ionization chambers are modeled either from blueprints or manufacturers’ user’s manuals. The dose-to-air in the chamber is calculated using the EGSnrc user-code egs_chamber using 11 different tabulated clinical photon spectra for the incident beams. The dose to a small volume of water is also calculated in the absence of the chamber at the midpoint of the chamber on its central axis. Using a simple equation, is calculated from these quantities under the assumption that is constant with energy and compared to TG-51 protocol and measured values.

Results:

Polynomial fits to the Monte Carlo calculated factors as a function of beam quality expressed as and are given for each ionization chamber. Differences are explained between Monte Carlo calculated values and values from the TG-51 protocol or calculated using the computer program used for TG-51 calculations. Systematic uncertainties in calculated values are analyzed and amount to a maximum of one standard deviation uncertainty of 0.99% if one assumes that photon cross-section uncertainties are uncorrelated and 0.63% if they are assumed correlated. The largest components of the uncertainty are the constancy of and the uncertainty in the cross-section for photons in water.

Conclusions:

It is now possible to calculate directly using Monte Carlo simulations.Monte Carlo calculations for most ionization chambers give results which are comparable to TG-51 values. Discrepancies can be explained using individual Monte Carlo calculations of various correction factors which are more accurate than previously used values. For small ionization chambers with central electrodes composed of high-Z materials, the effect of the central electrode is much larger than that for the aluminumelectrodes in Farmer chambers.

Loading

Full text loading...

/deliver/fulltext/aapm/journal/medphys/37/11/1.3495537.html;jsessionid=0HjqsEh97f3WXY9T3w3W5SJI.x-aip-live-02?itemId=/content/aapm/journal/medphys/37/11/10.1118/1.3495537&mimeType=html&fmt=ahah&containerItemId=content/aapm/journal/medphys
true
true

Access Key

  • FFree Content
  • OAOpen Access Content
  • SSubscribed Content
  • TFree Trial Content
752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
/content/realmedia?fmt=ahah&adPositionList=
&advertTargetUrl=//oascentral.aip.org/RealMedia/ads/&sitePageValue=online.medphys.org/37/11/10.1118/1.3495537&pageURL=http://scitation.aip.org/content/aapm/journal/medphys/37/11/10.1118/1.3495537'
Right1,Right2,Right3,