Sparse volume rendering on hardware?

I need to do real-time volume rendering of sparse data (medical and mining), when previously I've only done it using dense data (with straightforward ray marching through a 3D texture in the shader). I notice that since 5.3 Unreal has SVT but don't see any info on the rendering alrogithm used, and overall I get few other hits for sparse volume rendering. I don't see a clear way how rendering sparse data can be made efficient when neighboring ray marches in a thread group will not generally be in lockstep (e.g. variable step number, incoherent texture access, and dependent texture fetches per march iteration all seem quite horrible things). What are solutions?