Sorry to hear that Levi has cancer but happy to tell you that I believe that you made the right decision. I too struggled with the decision. Actually at the time of diagnosis I was like "No Way!!! I am not cutting off my Dog's leg!!!!! " The vet told me we could keep her more comfortable with pain meds until the pain got to be too much. He told me she had about 6 months to live. When her pain got to be too much then we would have to put her to sleep. Well for some reason I thought I would have months before the pain was too bad for her to live with because at the time of diagnosis the pain meds initially worked great. I took her for walks and everything. But it wasn't long before the pain meds stopped working. We upped the dosages and added in new ones but nothing helped. She was just miserable and that's when I decided that I would indeed amputate my Dog's leg. It became so clear to me when she was in so much pain. I was not ready to let her go yet. At this point it had been 6 weeks since her diagnosis and I scheduled the surgery for as soon as possible. My situation was a bit worrisome though because I have a very large Great Dane and I worried that she wouldn't be able to hold her huge body up on only one front leg. She has a very large upper body with a very wide chest. It just seemed like she wouldn't be able to get around with a missing leg. Even the vet said he was unsure of how she would do with that. Then I started investigating extra large Dogs and amputation on the computer and I found loads of inspiration. Especially on this site. On other sites also I found lots of stories and videos of plenty of Great Danes and other Xlarge dogs that had amputations and were doing great. I couldn't believe my eyes to see Great Danes running around on three legs like it had always been that way! I showed them to my husband and I was crying saying "I think she can do it!!!"  My Dog's name is Valentina and she is such a strong muscular Dog and after seeing all of the videos of other Dog's I felt confident that she would be able to walk as a tripawd. Seeing her for the first time after the surgery was very shocking and frightening but I stayed strong and acted normal while visiting her. Of course I broke down after I left but I knew I had to be strong around her to get her through this. Valentina did end up having some complications after her surgery and she had a long hard road to recovery. About 5 weeks until things started to get better.  But it was so worth it. She is Vibrant and happy now and we have spent so much quality time together and I will be forever thankful for that. She is now 14 weeks and 4 days post op and we couldn't be happier!!! We decided not to do chemo because after her rocky recovery I didn't want to do anything else to her to make her possibly feel bad.   Good Luck with Levi's recovery. It will be hard and yes you will probably doubt if you did the right thing. I definitely did. Especially when Val had the complications. I think I took everything harder than she did though. Having her back to her normal self is priceless and I would never go back and change my decision. By the way I also have a Doberman. She is not a tripawd nor does she have cancer. She is a 9yr old red Dobie. Her name is Emalee. She is an awesome Dog. Very serious and protective and she is extremely well behaved. Praying for you and your beautiful Doberman as the two of you together travel through this experience. It will change you. But I believe for the Good!!!