S. Karrer, “Repetitive Daylight Photodynamic Therapy versus Cryosurgery for Prevention of Actinic Keratoses in Photodamaged Facial Skin: A Prospective, Randomized Controlled Multicentre Two-armed Study”, Acta Derm Venereol, vol. 101, no. 1, p. adv00355, Jan. 2021.