This International Standard specifies the performance requirements of RADIOTHERAPY DOSIMETERS, intended for the measurement of ABSORBED DOSE TO WATER or AIR KERMA (and their rates and spatial distributions) in PHOTON, ELECTRON, proton or heavy ion RADIATION FIELDS as used in RADIOTHERAPY. The DOSE MONITORING SYSTEMS incorporated in RADIOTHERAPY treatment machines are not covered by this standard, neither are the re-entrant IONIZATION CHAMBERS used for BRACHYTHERAPY source calibration and constancy check devices. This standard is applicable to the following types of dosimeter: a) FIELD-CLASS DOSIMETERS normally used for 1) the measurement of KERMA or dose in a RADIATION BEAM, either in air or in a PHANTOM; 2) in vivo skin surface or intracavitary measurements of dose on PATIENTS. b) REFERENCE-CLASS DOSIMETERS normally used for the calibration of FIELD-CLASS DOSIMETERS; NOTE REFERENCE-CLASS DOSIMETERS may be used as FIELD-CLASS DOSIMETERS. c) SCANNING-CLASS DOSIMETERS normally used for relative dose distribution measurements with a SCANNING SYSTEM such as an automatic water PHANTOM.