Never think you are copping out! I got very close to stopping around number 9. My feet were painful, badly nerve affected (it's possible to lose feeling and have pain at the same time I discovered) and I was fearful about not being able to walk. My oncologist was sympathetic but keen for me to continue so we took it week by week, checking nothing for worse. I would definitely not have finished all 12 if I hadn't discovered a lump under my right arm (unrelated and totally benign)! Nearly five years later I still have damaged feet, it doesn't always rectify completely. It doesn't affect me much, I was never a runner, but it's annoying at times. You have had two thirds of the recommended amount and to be honest most consider 80% of the recommended treatment will be therapeutic (or not). You still have other treatment regimes to go through so if your oncologist feels the impact is too great, I'd be inclined to listen. Best wishes whatever you decide.