I have a willow tree that I pruned back most of the top. Now I have sprouts coming out all over the trunk. I can cut off the new sprouts in unwanted areas, But is there a way to keep them from coming back?
Your basic problem is that the harder you prune the tree, the more it will try to grow, until you finally go a step too far and kill it.
But the chances of killing a well established willow tree are just about zero. They will even regrow after a stump grinder has taken out the root ball to a foot (30cm) below ground level!
Willow is also one of the fastest growing trees, even before you provoked into growing even faster.
What you did to your tree is called "pollarding" which was traditionally done to produce lots of thin, fast growing branches which can be harvested for weaving baskets, etc, or as firewood. The new growth was cut right back every one or two years, and the tree will continue producing more indefinitely.
Coppicing is basically the same as pollarding, except you cut right down to ground level rather than leaving a few feet of the original trunk. Pollarding had the advantage that animals like rabbits can't eat the new shoots as soon as they appear, but apart from that there is no real difference.
A couple of pictures here of how your willow is trying to develop after you pruned it, if you just let it do it's thing for a couple of years. Trying to fight it is going to be tough!
Trying to turn your willow back into "something that looks like a tree" is probably a lost cause. If you want to start a new tree, you can easily grow one from a cutting. Just wait till a few of the shoots are two feet long, cut them off at the base, stand them in a bucket full of water, and ignore them (except for topping up the water as required). They will grow roots in a few weeks. Then plant them and give them a bucket of water every day until they get going. It is impossible to over-water willow trees.
Alternatively, use the new growth to make a "living sculpture" or a garden feature like a shelter for a seat. There are plenty of videos on the web with more detail, but you won't do any damage by "getting it wrong" - just prune off your mistake, and start again!