IEC 60731:2011 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. IEC 60731:2011 is applicable to the following types of dosimeter: a) field-class dosimeters normally used for 1) in vivo skin surface or intracavitary measurements of dose on patients. 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; c) scanning-class dosimeters normally used for relative dose distribution measurements with a scanning system such as an automatic water phantom. The object of this standard is: - to establish requirements for a satisfactory level of performance for radiotherapy dosimeters; - to standardize methods for the determination of compliance with this level of performance. Three levels of performance are specified: - a lower level of performance applying to field-class dosimeters; - a higher level of performance applying to reference-class dosimeters; - a specific level of performance applying to scanning-class dosimeters. This third edition cancels and replaces the second edition published in 1997 and its Amendment 1 (2002) and constitutes a technical revision. The technical modifications versus the second edition of this standard concerns performance requirements of radiotherapy dosimeters intended for the measurement of absorbed dose to water or air kerma in heavy ion radiation fields and scanning-class dosimeters normally used for relative dose distri...