In this phase 3 , randomized , double-blind , vehicle-controlled study ( NCT01541553 ) , patients 18 years with four to eight clinically typical , visible , discrete AKs within a contiguous 25-cm2 treatment area on the face or scalp underwent cryosurgery followed 3 weeks later by once-daily ingenol mebutate 0.015 % or vehicle gel for 3 consecutive days .