Yes to radiotherapy. It might not be strictly necessary, but you just don't know that for sure. Also, presumably you agreed to chemo because you wanted to take precautions, so why go through all the grot of chemo and not finish the job ?. It's like taking out an insurance policy you know won't give you full cover.
Of course nobody should subject themselves to radiation unecessarily, and there is no guarantee that RT will make any difference, but it's a case of deciding what your greatest threat is at the moment (and I would say it's BC).
Try not to let scare stories about RT being nasty influence you. I've had RT several times / know many people who have had it, and have never heard anyone say it is worse than chemo. It sometimes causes tiredness, and soreness for a few days (and a few people experience sickness), but SE's are nothing compared to the zombie chemo, FEC T.
