Mysti was a TDI dog, she did excellent on her test, they base it off the CGC test, and add a few things to it, and if they pass they can get their CGC at the same time. Though I think that may depend on the facility doing the testing, I am not sure. TDI has requirements yearly to recertify, as mentioned above, but they are pretty easy, and a yearly renewal fee as well, which if I recall is not alot. Once certified, you should check with the places you wish to visit and see what their policies are, they might have their own regulations for visiting. The hospital we went to had a list of requirements we had to meet in order to visit. We had to sign up as a volunteer of the hospital and sign some paperwork for them, including insurance waivers and other health related stuff, but it is all pretty standard stuff for volunteers, you should check into it ahead of time though. The work is very rewarding, and gives you a very good feeling of helping others, and the dogs either love it or they hate it. Mysti loved it! It is good for the ones that take to it, it also helps to promote our breed and its always good to get ambassadors for our breed out there doing good things!!
I hope all of this helped you and I hope you and Vader enjoy doing the therapy work as much as Mysti and I did. He is a great looking dobe and I am sure he will have no problem passing his test!! Good luck!