The prepublication for the NCS subcommittee on linac QA, including FFF, is online.
Please send your comments to the chair of this subcommittee.
Note that the full publication is still far from completion.
The publication can be found on the website for the subcommittee
https://radiationdosimetry.org/ncs/quality-control-for-linear-accelerators
Best, on behalf of NCS 33,