Queen sac to break 1900


A correspondance game that allowed me to break 1900 for the first time.  The opening went really well for me & my opponent missed a tactic.  I have to admit that I was running low on ideas by move 18 and spent two days considering the move.  Alternatives:

c4 seemed to lead to pawn exchanges (maybe a & b going) freeing my opps position somewhat.

doubling rooks i felt i wouldnt really penetrate.

Any thoughts on a plan from move 18????