Can you say 

> 
> Despite initial success, method A has not found its way into the canon
>  of cancer treatments.
> 
> 
> 

What I mean by "canon" is simply that method A is not one of those that a normal doctor at a normal hospital would suggest or would have learned about during his studies.

Looking at [Merriam-Webster's](https://www.merriam-webster.com/dictionary/canon) definition, I think that the 4.th meaning might cover my usage, but I am not sure because the focus there is on 'principles', not 'methods'. Similarly, [most other definitions](https://dictionary.cambridge.org/dictionary/english/canon) [that I looked at](https://en.oxforddictionaries.com/definition/canon) are even more limited to religious, poetic, or musical meaning.