In 2007, the European Commission (EC) commissioned a group of experts to undertake the revision of Report Radiation Protection (RP 91) 'Criteria for acceptability of radiological (including radiotherapy) and nuclear medicine installations' written in 1997. The revised draft report was submitted to the EC in 2010, who issued it for public consultation. The EC has commissioned the same group of experts to consider the comments of the public consultation for further improvement of the revised report. The EC intends to publish the final report under its Radiation Report Series as RP 162. This paper describes the background to the selection of the key performance parameters for radiotherapy equipment and sets out the sources of their criteria of acceptability including suspension levels for a wide range of radiotherapy equipment.