Applies to medical electron accelerators when used, for therapy purposes, in human medical practice. This standard applies to medical electron accelerators which deliver a radiation beam of either X-radiation or electron radiation with nominal energies in the range 1 MeV to 50 MeV at maximum absorbed dose rates between 0,001 Gy s-1 and 1 Gy s-1 at 1 m from the radiation source and at normal treatment distances between 50 cm and 200 cm from the radiation source. The present standard describes measurements and test procedures to be performed by the manufacturer at the design and construction stage of a medical electron accelerator but does not specify acceptance tests to be performed after installation at the purchaser's site. The accompanying report, IEC 60977, however, does suggest that many of the test procedures are appropriate for acceptance tests. The measurement conditions described in the present standard differ from those previously in use. This applies particularly to the phantom position for measurements and the measurement of distances from the isocentre. These new conditions should be substituted for and not be added to previous methods. This standard specifies test procedures for the determination and disclosure of functional performance characteristics, knowledge of which is deemed necessary for proper application and use of a medical electron accelerator and which are to be declared in the accompanying documents together with the greatest deviation or variation to be expected under specific conditions in normal use. A format for presentation of functional performance values is given in Annex A. It is recognized that inaccuracies in the test methods must be allowed for when assessing performance. However, it was not felt to be advisable to combine the errors into an overall performance tolerance but to keep them separate in the expectation that more accurate test methods will be evolved. It is not intended that this standard should in any way inhibit the future development of new designs of equipment which may have operating modes and parameters different from those described herein, provided that such equipment achieves equivalent levels of performance for the treatment of patients. Except where otherwise stated this standard assumes that the medical electron accelerators have an isocentric gantry. Where the equipment is non-isocentric, the description of performance and test methods may need to be suitably adapted. This second edition cancels and replaces the first edition published in 1989. It constitutes a technical revision. This second edition includes the addition of performance standards and test methods relating to the following new technologies: - dynamic beam delivery techniques, such as moving beam radiotherapy, intensity-modulated radiation therapy (IMRT), image-guided radiotherapy (IGRT) and programmable wedge fields; - stereotactic radiotherapy (SRT) / stereotactic radiosurgery (SRS); - use of electronic imaging devices. This standard, together with IEC TR 60977, should be read in conjunction with IEC 60601-2-1.