NOTE 1 If, for certain medical electrical systems, special radiation fields are required such that the scope of IEC 60806 does not apply (e. g., using CT collimators with bow-tie filters), the appropriate system particular standard applies.

NOTE 2 In practical use air kerma or air kerma rate are the most practical physical measures to quantify X-ray patterns.

NOTE 3 The maximum symmetrical radiation field can change from its initial value as the X-ray tube ages through use.