IEC 60601-2-1:2020 applies to the BASIC SAFETY and ESSENTIAL PERFORMANCE of ELECTRON ACCELERATORS, hereafter referred to as ME EQUIPMENT, in the range 1 MeV to 50 MeV, used for TREATMENT of PATIENTS. NOTE 1 While ELECTRON ACCELERATORS used for TREATMENT of PATIENTS are always ME EQUIPMENT, there are times in this document where they are referred to as EXTERNAL BEAM EQUIPMENT (EBE). Usage of EBE does not remove the requirements placed on the ME EQUIPMENT but is meant to clarify that the ME EQUIPMENT being discussed is the EBE and not some other ME EQUIPMENT that may be part of the system configuration. This particular standard, with the inclusion of TYPE TESTS and SITE TESTS, applies to the manufacture and some installation aspects of ELECTRON ACCELERATORS and their included equipment used to increase the precision, accuracy and volumetric targeting of the TREATMENT delivery – intended for RADIOTHERAPY in medical practice, including those in which the selection and DISPLAY of TREATMENT PARAMETERS can be controlled automatically by PROGRAMMABLE ELECTRONIC SUBSYSTEMS (PESS), – that, under NORMAL CONDITIONS and in NORMAL USE, deliver a RADIATION BEAM of X-RADIATION or ELECTRON RADIATION having • NOMINAL ENERGY in the range 1 MeV to 50 MeV, • maximum ABSORBED DOSE RATES between 0,001 Gy x s–1 and 1 Gy x s–1 at the ERP from the RADIATION SOURCE, and • REFERENCE TREATMENT DISTANCES (RTDs) between 0,5 m and 2 m from the RADIATION SOURCE; and – intended to be • for NORMAL USE, operated under the authority of the RESPONSIBLE ORGANIZATION by QUALIFIED PERSONS appropriately licensed or having the required skills for a particular medical application, for particular SPECIFIED clinical purposes, • maintained in accordance with the recommendations given in the INSTRUCTIONS FOR USE, and • subject to regular QUALITY ASSURANCE performance and calibration checks by a QUALIFIED PERSON. IEC 60601-2-1:2020 cancels and replaces the third edition published in 2009 and Amendment 1:2014. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) alignment with the new relevant collateral standards; b) addition of computer interface and control; c) addition of new technologies in RADIOTHERAPY, including • BEAM GATING, and • ADAPTIVE RADIOTHERAPY.