The paper describes the Monte Carlo calculation of diaphragm correction factors for free-air ionization chamber standards. Although not submitted for publication until December 2008, this work was carried out in 2006 and preliminary results were presented at the World Congress on Medical Physics and Biomedical Engineering of that year (Kessler 2006). Subsequently, Mainegra-Hing et al (2008) published the results of similar calculations for their own standard. In retrospect, the authors regret that they did not take the opportunity to revise their manuscript to include a citation to the work of Mainegra-Hing et al.

The following sentence should be added at the end of the second paragraph of section 7 (Discussion) on page 2744 (following the text '...correction for diaphragm scatter.'):

'In a more recent work, Mainegra-Hing et al (2008) calculated a combined correction for diaphragm transmission and scatter of 0.9984 for their 250 kV measurement conditions. This is in agreement with the value 0.9983(3) obtained in the present work.'

References

Kessler C 2006 Calculation of the aperture scatter and transmission correction factors for the BIPM free-air chamber standards using the code PENELOPE World Congress on Medical Physics and Biomedical Engineering (27 August–1 September 2006, Seoul, Korea)

Mainegra-Hing E, Reynaert N and Kawrakow I 2008 Novel approach for the Monte Carlo calculation of free-air chamber correction factors Med. Phys. 35 3650–60