I have absolutely no idea of an accurate answer to your question. However I would be very interested to know which meds your Dr is advising against (preds, Imuran, cellcept are the three used most often with other immunosuppressants being used with not so much statistical success. Have you had a IgG4 test done? If yes and if positive result, then I think that the med most often used is Rituximab infusions instead of imuran or cellcept.
Please remember that your treatment to date (as outlined above) is only treating the symptoms of RF. The ureterolysis wrap surgery only protects your ureter from future RF growth. It does not stop or slow down RF. However there have been cases where the RF has spontaneously stopped growing and in a few even receeded. The reason for this has not been published, but my personal thought is that the patient's diet and outlook may have a lot to do with it. Thinking positively can not hurt. As to diet see if you can eat what is referred to as anti-inflammatory foods. See:
There are a few places on-line where you might be able to get answers that have a lot more activity that this site.
When you post it would help for you to give a brief history including who, where, age, care, meds, diagnosis, how was it determined, and most importantly are your Drs familiar with the disease. It sounds like they are from what you posted and you listed some of the answers already.
Since I see multiple messages on/from multiple RF/RPF support groups, I offer the following in response to your note. Maybe it will help others in the same quandry and won't get the higher-ups at Careplace too mad at me.
Yahoo RF World (https://groups.yahoo.com/neo/groups/retroperitoneal_fibrosisworldsupport/info) has over 650 members and very extensive files, information, links, etc and is a very resource rich group with multiple daily postings.
There is also a very active Facebook group (https://www.facebook.com/groups/60126946140/) which has many posts per day and is the easiest place to discuss any issues, but does not have the resources that the Yahoo World group has. There are a few other FB groups with memberships numbering perhaps a total of a few dozen with lots of overlap, so probably only a dozen or two individuals.
As here at Careplace, there are multiple Drs and other medically trained members, but it is rare for Dr to respond to a medical question for legal and professional reasons. Many of the Nurses who are members do respond, but none of them boast of their credentials.
Membership in either of these groups is easy. All that you have to do is sign in with a Yahoo ID to join the Yahoo World group. (Joining the Yahoo World group will result in a welcome message and two attachments, one which hopefully explains how to navigate the Yahoo world sit, the other which might help you understand RF and the customary treatment process.) Joining the FB group requires approval by an existing member. Approvals are usually done within hours of a request to join.
A major difference in the groups structure is that membership lists, emailing, reference materials, links to other support information, etc appears to be most open (and most easily accessible) on the yahoo world group and hardest to access on Careplace.
It's been so long since I received a message from this Careplace group that your post came as a surprise. (yes I belong to all three, but rarely respond to other than Yahoo World and FB since they are the active ones.)
Hope that this helps and isn't too longwinded.