I have survived a few pregnacies working in a critical care area. Also had my share of miscarrages when I was young. Good luck. Unfortunately, because of the seriousness of where u work, u almost have to tell ur co workers now. Radiology is always around, invasive procedures being done and such, make one want to be more careful, and ur co workers will help if they know. With universal precautions,you will be protected from most except airborne, so be careful. I really never worried. I am so careful with precautions that I felt fairly safe. I was always careful with lifting in the first three, getting more help then I usually would.
As far as telling ur boss, I would just let them know when u tell everyone else, sooner then later. They r use to planning for leaves. You r under no obligation to tell them right away, but it helps for vacations and such. Many nurses and other employees become pregnant soon after starting a job, one boss of mine would have said, "it is what it is",,,lol. Have fun and good luck!