You can refuse a feeding tube but the side effect may be death by starvation or dehydration. you should inform yourself about the process. Read more
http://www.livestrong.com/article/39934-process...
Living with a tube may be a better choice. Talk to a therapist or loved one.
Even with a power of attorney or DNR?
You have the choice, although sometimes if you lose consciousness, you may lose that option, papers or not. I have had firsthand experience with this.