Weather radar points forward. You know this. Does that mean its safe? Who the heck knows.
What I believe is this...if you're worried about wx radar and health issues, you should also be worrying about the affect on your body of all the other electro magnetic thingeys we deal with in aviation and in everyday life. All those wire bundles under the floor in the aircraft...lovely electrical fields! Your mobile phone? Hope you don't get brain cancer (or, for that matter, testicular cancer from having it in your pocket).
I can't really see any reason to turn it off in flight...what little danger there is would be if you were directly in front of it and, at altitude, thats not real likely.
At the end of the day, if you want to turn it off in flight if the weather is nice,and it doesn't violate your ops manual, fill your boots.
(And before you say, 'what does he know about wx radar', my helo has weather radar...I just don't use it at 30,000').
HP