A cryo-system for treating a body part of an individual by cryotherapy, which includes two parts. The first part is either i) a cryo-probe suitable for internal cooling, which includes a penetrating segment in communication with a cryogen source and is at least smaller than 1/10th of the body part's biggest volume and/or at least one dimension smaller than 1 cm or ii) a cryo-probe suitable for external cooling, which includes a non-penetrating segment in communication with a cryogen source. The second part is either i) an assembly of at least two nanoparticles bound to each other or associated with each other via binding or associating material or ii) at least one nanoparticle, which includes iron and at least one other metal than iron. The assembly of at least two nanoparticles or the at least one nanoparticle may be cooled by the cryo-probe or by switching on the cryo-probe.