The purpose of this report is twofold: to provide guidelines to Secondary Standards Dosimetry Laboratories (SSDLs) on how to establish a standard of absorbed dose to water in a 60Co gamma ray beam, and to provide guidelines to clinical physicists on the changes that can be expected when IAEA Technical Reports Series No. 398 (TRS-398) is adopted in a hospital environment in place of another code of practice based on air kerma standards. The results of measurements made with 60Co beams, low and medium energy X ray beams, high energy photon and electron beams, and proton and heavy ion beams are grouped in tabular and graphical forms for different ionization chambers and beam energies, showing the expected differences in absorbed dose determination between TRS-398 and other existing codes of practice.