Original paper| Volume 77, P176-180, September 2020

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Dosimetric impact of failing to apply correction factors to ion recombination in percentage depth dose measurements and the volume-averaging effect in flattening filter-free beams

Published:August 29, 2020DOI:


      • Application of the kS factor in PDD(10) and kvol in FFF beams could be essential.
      • Error combination in dose calibration of FFF beams could otherwise approach 2%.
      • Error combination in FFF beams calibration for most common chambers is within 1%



      To examine whether it is essential to apply correction factors for ion recombination (kS) to percentage depth dose (PDD) measurements and to the volume-averaging effect (kvol) to ensure accurate absolute dose calibration for flattening filter-free (FFF) beams for the most commonly used ionization chambers.


      We surveyed medical physicists worldwide (n = 159) to identify the five most common ionization chamber combinations used for absolute and relative reference dosimetry of FFF beams. We then assessed the overall absolute dose calibration error for FFF beams of the Artiste Siemens and TrueBeam Varian linear accelerators resulting from failing to apply correction factors kS in the PDD(10) and the volume-averaging effect (kvol) to such chamber combinations.


      All the chamber combinations examined—the Farmer PTW 30013 ionization chamber used for absolute dosimetry, and the PTW 31010, PTW 30013, IBA CC04, IBA CC13, and PTW 31021 ionization chambers used for PDD curves measurements—showed non-negligible errors (≥0.5%). The largest error (1.6%) was found for the combination of the Farmer PTW 30013 chamber with the IBA CC13 chamber, which was the most widely used chamber combination in our survey.


      Based on our findings, we strongly recommend assessing the impact of failing to apply correction factors kS in the PDD(10) and kvol prior to using any chamber type for FFF beam reference dosimetry purposes.


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