UNKNOWN
This is entirely arbitrary, this is work that's been carried out by some Chinese workers in Tailing city, Lan and others, and it is based on Chinese standards and looking at radiography in Chinese subjects in all the Chinese over a period of time, and basing it on their work.  We in fact tried to repeat their works and we found that we couldn't.  Personally I think quite frankly, what they are suggesting is perhaps too rigorous and your word "over-kill", I think is quite appropriate in its use.  I think one has to use one's judgement with these sort of cases, and that is precisely what we did.  We are obviously aware of all the different methods involved, but at the end of the day, we use a method which we happy with and we stick by it.  And that is how we do it.