CAN/CSA-C22.2 NO. 60601-2-1A-01 (R2007)

Subclause 29.3.1.1 of IEC 60601-2-1:1998 sets limits to X-ray leakage radiation through beam limiting devices (BLDs) in the patient plane in order to reduce the detrimental effects on the patient due to leakage radiation. This clause restricts leakage through the main X and Y BLDs to a maximum of 2 % and an average of 0,5 %. Multi-element BLDs were assumed to replace a beam shielding block which attenuated the beam to about 5 %, and this was the upper limit applied to multi-element BLDs.

With the growth of techniques such as conformal therapy and IMRT, multi-element BLDs (which allow higher leakage levels) are being used to shield more of the radiation field area than was the case with conventional techniques using beam blocks. It is now proposed in the replacement subclause 29.3.1.1 to set a leakage tolerance on the total beam limiting system (the X and Y BLDs themselves may be single element, multi-element, or a combination of both) and to limit the leakage to an average of 0,75 %.