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Experimental determination of the effective point of measurement for cylindrical ionization chambers in megavoltage photon beams

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Abstract

Current dosimetry protocols specify an effective point of measurement (EPOM) shift of 0.6r for a cylindrical ionization chamber in photon beams. However, prior studies have reported that this shift was excessively large. The objective of this study was to experimentally evaluate the EPOM shifts in photon beams for cylindrical ionization chambers, which are widely used in clinical practice, and thus determine the appropriate EPOM shift. A microdiamond detector, which is a semiconductor detector with a small sensitive volume, was used as a reference detector, and the EPOM shifts of 11 types of cylindrical ionization chambers were evaluated at 6 MV and 10 MV. The depth shift from the percent depth dose (PDD) of the reference detector to that of the evaluated chamber was calculated using the least-squares method and was defined as the EPOM shift. The EPOM shift of the 10 MV condition was slightly larger than that of the 6 MV condition. However, because this trend was not observed for all chambers, the results of the two energies were averaged, and the EPOM shifts were determined to be 0.33r–0.43r (± 0.05) for 10 types of ionization chambers, and 0.03r (± 0.03) for the A1SL chamber. The shifts for all ionization chambers were smaller than 0.6r, indicating that the recommended EPOM shifts were overestimated and the absorbed dose was underestimated at the calibration depth. Hence, the appropriate EPOM shift of the 10 types of ionization chambers was 0.4r (the geometric center of the A1SL chamber), with a dose uncertainty of 0.05%.

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References

  1. International Atomic Energy Agency. Absorbed dose determination in external beam radiotherapy: an international code of practice for dosimetry based on standards of absorbed dose to water. Vienna, Austria: Technical Reports Series; 2000. 398.

  2. McEwen M, Dewerd L and Ibbott G, et al. Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon beams. Med Phys. 2014. 41(4):041501–041520.

    Article  PubMed  PubMed Central  Google Scholar 

  3. Japan Society of Medical Physics. Standard dosimetry of absorbed dose to water in external beam radiotherapy. Tokyo: Tsusho-sangyokenkyusya; 2012. (in Japanese).

  4. Kawrakow I. On the effective point of measurement in megavoltage photon beams. Med Phys. 2006;33(6):1829–39.

    Article  PubMed  Google Scholar 

  5. Tessier F, Kawrakow I. Effective point of measurement of thimble ion chambers in megavoltage photon beams. Med Phys. 2010;37(1):96–107.

    Article  CAS  PubMed  Google Scholar 

  6. Muir BR, Rojers DWO. Monte Carlo calculations of electron beam quality conversion factors for several ion chamber types. Med Phys. 2014;41(11): 111701.

    Article  CAS  PubMed  Google Scholar 

  7. McEwen M, Kawrakow I, Ross CK. The effective point of measurement of ionization chambers and the build-up anomaly in MV x-ray beams. Med Phys. 2008;35(3):950–8.

    Article  CAS  PubMed  Google Scholar 

  8. von Voigts-Rhetz P, Czarnecki D, Zink K. Effective point of measurement for parallel plate and cylindrical ion chambers in megavoltage electron beams. Z Med Phys. 2014;24(3):216–23.

    Article  Google Scholar 

  9. Wang LL, Rojers DWO. Study of the effective point of measurement for ion chambers in electron beams by Monte Carlo simulation. Med Phys. 2009;36(6):2034–42.

    Article  CAS  PubMed  Google Scholar 

  10. Wang LL, Rojers DWO. Replacement correction factors for cylindrical ion chambers in electron beams. Med Phys. 2009;36(10):4600–8.

    Article  CAS  PubMed  Google Scholar 

  11. Looe HK, Harder D, Poppe B. Experimental determination of the effective point of measurement for various detectors used in photon and electron beam dosimetry. Phys Med Biol. 2011;56(14):4267–90.

    Article  PubMed  Google Scholar 

  12. Paul KC, Hartmann GH, Zakaria GA. Study on the displacement effect at cylindrical ionization chambers in high energy photon of flat and true beams. J Bangladesh Acad Sci. 2017;41(2):227–35.

    Article  CAS  Google Scholar 

  13. Delfs B, Kapsch RP, Chofor N, et al. A new reference-type ionization chamber with direction-independent response for use in small-field photon-beam dosimetry—an experimental and Monte Carlo study. Zeitschrift Med Phys. 2019;29(1):39–48.

    Article  Google Scholar 

  14. Wegener S, Sauer OA. The effective point of measurement for depth-dose measurements in small MV photon beams with different detectors. Med Phys. 2019;46(11):5209–15.

    Article  CAS  PubMed  Google Scholar 

  15. Huang Y, Willomitzer C, Zakaria GA, et al. Experimental determination of the effective point of measurement of cylindrical ionization chambers for high-energy photon and electron beams. Phys Med. 2010;26(3):126–31.

    Article  PubMed  Google Scholar 

  16. Seif F, Karbalayi M, Bayatiani MR, Tahmasebi-Birgani MJ, et al. Effective point of measurement in cylindrical ion chamber for megavoltage photon beams. Iran J Med Phys. 2013;10(3):147–55.

    Google Scholar 

  17. Laub W, Kaulich TW, Nüsslin F. Clinical radiation therapy measurements with a new commercial synthetic single crystal diamond detector. J Appl Clin Med Phys. 2014;15(6):92–102.

    Article  PubMed Central  Google Scholar 

  18. Ravichandran R, Binukumar JP, Al Amri I, et al. Diamond detector in absorbed dose measurements in high-energy linear accelerator photon and electron beams. J Appl Clin Med Phys. 2016;17(2):291–303.

    Article  PubMed  PubMed Central  Google Scholar 

  19. Marinelli M, Prestopino G, Verona C, et al. Experimental determination of the PTW 60019 microDiamond dosimeter active area and volume. Med phys. 2016;43(9):5205–12.

    Article  PubMed  Google Scholar 

  20. National Institute of Technology and Evaluation Certification Center. "An Introductory guide of uncertain measurement". https://www.nite.go.jp/data/000050641.pdf. Accessed 18 May 2021.

  21. Lacroix F, Guillot M, McEwen M, et al. Extraction of depth-dependent perturbation factors for parallel-plate chambers in electron beams using a plastic scintillation detector. Med Phys. 2010;37(8):4331–42.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  22. Simiele E, Smith B, Culberson W. Experimental determination of the effective point of measurement in electron beams using a commercial scintillation detector. Radiat Meas. 2017;107:1–6.

    Article  CAS  Google Scholar 

  23. Tessier F, Hooten B, McEwen M. Zero-shift thimble ionization chamber. Med Phys. 2010;37(3):1161–3.

    Article  PubMed  Google Scholar 

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Acknowledgements

Authors are thankful for the material support of Takahiro Isohama from TOYO MEDIC corporation, Takushi Senda from EURO MEDTECH corporation and Hiroaki Ushiba from CHIYODA TECHNOL corporation.

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Authors and Affiliations

  1. Nagoya University Graduate School of Medicine, Nagoya, Aichi, Japan

    Yukiko Iwafuchi, Hiroshi Oguchi & Kota Yamamoto

  2. Nagoya University Hospital, Nagoya, Aichi, Japan

    Kuniyasu Okudaira

Authors
  1. Yukiko Iwafuchi
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  2. Hiroshi Oguchi
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  3. Kuniyasu Okudaira
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  4. Kota Yamamoto
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Correspondence to Hiroshi Oguchi.

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Iwafuchi, Y., Oguchi, H., Okudaira, K. et al. Experimental determination of the effective point of measurement for cylindrical ionization chambers in megavoltage photon beams. Radiol Phys Technol 15, 291–297 (2022). https://doi.org/10.1007/s12194-022-00669-z

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  • DOI: https://doi.org/10.1007/s12194-022-00669-z

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