You can convert any spell into a defense.
Prerequisites: Arcane spellcaster, caster level 10th.
Benefit: As a immediate action, you can sacrifice a prepared spell or unused spell slot of 1st level or higher and gain a deflection bonus to AC equal to the level of the spell or spell slot you sacrificed for 1 round. 0-level spells may not be sacrificed in this manner.
Advanced Player’s Guide. Copyright 2010, Paizo Publishing, LLC; Author: Jason Bulmahn.