Abstract: Disclosed is a device for contact radiotherapy, comprising a set of applicators, wherein each applicator comprises a hollow spherical head, with different diameters, the external surface of which is able to be in contact with a cavity of a living tissue and the internal surface of which defines an internal space able to receive a source of x-rays, with at least one area of the head is intended to have x-rays pass through it, and the thickness of said area depends on the diameter of the head configured so that the dose of x-rays produced at the external surface is between 18 and 22 gray. Also disclosed is a system for contact radiotherapy comprising said device. The disclosed device and system apply particularly to per-operative radiotherapy, in that the irradiation is produced in contact with the ablation bed of the tumour, in particular in the breast, during the operation.