I personally would be very unhappy if this was kept from me. I understand your motivation, but if it were my husband who did that to me, I would have a hard time being ok with it. It's his treatment/health, and not your choice to make.
You obviously know him better than anyone here, so it's your call to make, but my vote is to tell him separate from the rest of the family, and let him choose who to tell.
A few months ago my CT showed an "anomaly". I had to get a follow-up CT in 3 months to compare, so it was stressful, but I would still prefer to know than not. Had that been kept from me, I would have been furious.