ABSTRACT
Pedro Andreo and Alan Nahum
This appendix is intended to provide supplementary information on the codes of practice
for absolute dose determination which are described in Chapter 18. The origin of the various
factors involved in dose determination and the questions which are still to be resolved are
discussed. Only megavoltage photon and electron beams are dealt with. The proper choice for
stopping-power ratios and perturbation factors are dealt with in Section D.1 and Section D.2,
respectively. Section D.3 is dedicated to the specification of the beam quality. Section D.4
considers the issue of humidity correction for ionisation chambers. Finally, Section D.5
contains an estimation of the overall uncertainties in absolute dose determination in
reference conditions. For a better understanding of the concepts discussed in this appendix,
it is recommended that the reader familiarise her/himself with the codes of practice presented in
Chapter 18 and with the general characteristics of photon and electron beams presented in
Chapter 20, Chapter 22 and Chapter 24.
