Sorry, LAST thing. I promise. :)
I also meant if the multiple exposures (as opposed to one) would affect the (theoretical) question about how it would affect the sperm, physically or genetically.
Radiation damage is permanent and cumulative. So yes, multiple exposures to the same area would increase the radiation dose received.
One more time - the sperm that may have been in your body at the time of your VCUGs are no longer viable. They have been expelled and new sperm have taken their place.
I almost hate to say this, but if your testes were damaged by radiation, there is a slight possibility that they would produce defective sperm. It's a long shot, but it could happen.
Hope I didn't open a new can of worms with my last statement. I'm not sure I can give you any more advice than this. If you have any other questions, I recommend you ask my colleague Michael K. or another radiologist.
Try not to worry about things that haven't happened yet or those over which you have no control.