Pregnant and radiation exposure

I can't think of a good way to word this question,

Basically I'm going to be 31 weeks pregnant and my boyfriend's grandfather was just diagnosed with stage 4 lung cancer and has just started his radiation, my boyfriend's mother will not allow him to go see his grandfather because she says that he could transfer the radiation to me. How long would I have to stay away from him until it's safe to be around him again? And is it harmful for pregnant women to be around other people that have been exposed to someone going through radiation? Sorry it's such a lengthy question!