The trace amounts of butane would only be a concern for someone treating themselves for a serious disease like cancer. I believe we have immune systems for a reason, and most of ours could deal with the residue. Someone with a compromised immune system, not so much.
I'm so thrilled that you've improved so dramatically from your first attempt. This gives you one more option, and the concentrates are an excellent way to get a higher cannabinoid load into the system.
Are you using any high CBD strains for the chronic pain? I've found a 1:1 ratio works effectively for me, and a 2:1 CBD:THC works even better. It's still strange wrapping my head around cannabis that doesn't offer euphoria, but damn! Mighty effective stuff. I made CBD capsules and take three a day to eliminate rediculous pain in my upper back. Amazingly effective.
I'm beginning to form an opinion that it's most beneficial to get your cannabis from many different directions. The more varied your menu and delivery methods the greater benefit you should expect. Just a theory right now, and no way to prove it, but it sure feel right.