Decrement Lines: A New Presentation of data in Cobalt 60 Beam Dosimetry

A method of describing the dose distribution within a beam is outlined in which the dose distribution in a 60 Co beam is related to the central axis depth dose by use of “decrement lines” which are defined and shown to be families of straight lines for the Hunslet apparatus and possibly for the Orbitron. As compared with the usual method of preparing isodose charts, the decrement system is shown to reduce the necessary experimental work to very small amounts without loss of accuracy, and to have advantages in overall accuracy as a method of presentation of beam data.* The practical use of the system in the correction for surface obliquity and in the calculation of moving-field distributions is discussed.