Determination of consensus kQ values for megavoltage photon beams for the update of IAEA TRS-398

P. Andreo*, D. T. Burns, R. P. Kapsch, M. McEwen, S. Vatnitsky, C. E. Andersen, F. Ballester, J. Borbinha, F. Delaunay, P. Francescon, M. D. Hanlon, L. Mirzakhanian, B. Muir, J. Ojala, C. P. Oliver, M. Pimpinella, M. Pinto, L. A. De Prez, J. Seuntjens, L. SommierP. Teles, J. Tikkanen, J. Vijande, K. Zink

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


The IAEA is currently coordinating a multi-year project to update the TRS-398 Code of Practice for the dosimetry of external beam radiotherapy based on standards of absorbed dose to water. One major aspect of the project is the determination of new beam quality correction factors, kQ, for megavoltage photon beams consistent with developments in radiotherapy dosimetry and technology since the publication of TRS-398 in 2000. Specifically, all values must be based on, or consistent with, the key data of ICRU Report 90. Data sets obtained from Monte Carlo (MC) calculations by advanced users and measurements at primary standards laboratories have been compiled for 23 cylindrical ionization chamber types, consisting of 725 MC-calculated and 179 experimental data points. These have been used to derive consensus kQ values as a function of the beam quality index TPR20,10 with a combined standard uncertainty of 0.6%. Mean values of MC-derived chamber-specific fch factors for cylindrical and plane-parallel chamber types in 60Co beams have also been obtained with an estimated uncertainty of 0.4%.

Original languageEnglish
Article number095011
JournalPhysics in Medicine and Biology
Issue number9
Number of pages13
Publication statusPublished - 7 May 2020


  • Dosimetry
  • Ionization chambers
  • Monte Carlo
  • MV photon beams
  • TRS-398


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