So you have actually used one @poodlejules ?
The thyroid guard/collar has come up in threads now & then (I started a thread on them in April) - it seems not only are they not often used (I've never been offered one) - I am not sure they are even available, if asked for as we have buses!
Did you have to request it before you arrived for your mammogram? Was it in the Bus or an actual Imaging Office?
https://onlinenetwork.bcna.org.au/discussion/20766/have-you-been-offered-a-thyroid-guard-for-your-mammogram-increase-in-thyroid-cancer-blamed-on-rays#latest