Abstract
A linear accelerator’s output is periodically checked by using a reference ion chamber which is also periodically calibrated at the accredited standard dosimetry laboratories. We suggest a simple procedure for checking the chamber’s stability between calibrations by comparison with another ion chamber. To identify the long-term stability of chambers, we collected and assessed the dose-to-water conversion factors provided by standard laboratories for three chambers during a period of four years. To develop the chamber constancy check program, we used one Farmer-type reference ion chamber FC65-G, two ion chambers (CC13a and CC13b) and one CC01 ion chamber (IBA). Under the accelerator, each chamber was placed inside the solid phantom and irradiated; the experimental configurations were identical. To check the variation in charge collection of the reference chamber, we monitored the ratios of the FC65-G values over each chamber reading. Based on the error propagation of the two chamber ratios, we estimated the uncertainty of the output calibration from the chamber variation. The calibration factors provided for the three chambers showed 0.04 ∼ 0.12% standard deviations during four years. For procedure development, the reading ratios of FC65-G over CCxx showed very good stability; the ratios of FC65-G over CC13a, CC13b and CC01 varied less than 0.059, 0.087 and 0.248%, respectively, over five measurements. By ascribing possible uncertainties of the ratio to the reference chamber alone, we could conservatively check the stability of the reference chamber for treatment safety. An extension of the chamber calibration period was also evaluated. In conclusion, we designed a stability check procedure for the reference chamber based on a reading ratio of two chambers. This could help the user assess the chamber stability between periodic chamber calibration, and the associated patient treatment could be carried out with enhanced safety.
Similar content being viewed by others
References
International Commission on Radiation Units and Measurement, ICRU Report No. 24, 1976.
American Association of Physicists in Medicine Task Group 40, Med. Phys. 21, 581 (1994).
American Association of Physicists in Medicine Task Group 21, Med. Phys. 10, 741 (1983).
American Association of Physicists in Medicine, Report No. 86: Quality assurance for clinical trials. A primer for physicists (Medical Physics Publishing, Madison, 2004), p. 1.
American Association of Physicists in Medicine Task Group 142, Med. Phys. 36, 4197 (2009).
In Korea, the KRISS is the only PSDL and provides the chamber factors. The MFDS, formerly KFDA, used to provide the chamber factors as the SSDL, but did not at the time of this writing.
American Association of Physicists in Medicine Task Group 51, Med. Phys. 26, 1847 (1999).
International Atomic Energy Agency, IAEA Technical Report Series No. 398, 2001.
G. F. Knoll, Radiation Detection and Measurement, third ed. (John Wiley & Sons, New York, 2000).
P. Castro, F. Garcia-Vicente, C. Minguez, A. Floriano, D. Sevillano, L. Perez and J. J. Torres, J. Appl. Clin. Med. Phys. 22, 2676 (2008).
International Commission on Radiological Units and Measurement, ICRU Report No. 10b, 1962.
C. J. Karzmark, Med. Phys. 7, 574 (1980).
R. J. Barish and I. A. Lerch, Med. Phys. 19, 203 (1992).
M. R. McEwen, Med. Phys. 37, 2179 (2010).
G. A. Ezzell et al., Med. Phys. 30, 2089 (2003).
G. Rikner and E. Grusell, Phys. Med. Biol. 11, 1261 (1983).
M. Kapanen, M. Tenhunen, T. Hamalainen, P. Sipila, R. Parkkinen and H. Jarvinen, Phys. Med. Biol. 51, 3581 (2006).
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Kang, SK., Yoon, JW., Park, S. et al. Indirect check of the stability of the reference ion chamber used for accelerator output calibration. Journal of the Korean Physical Society 65, 1475–1480 (2014). https://doi.org/10.3938/jkps.65.1475
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.3938/jkps.65.1475