[en] Radiotherapy of certain tumor sites requires small-size fields of irradiation (≤ 4 cm) with a good dose plateau and a sharp dose gradient on the field border. Fot this purpose a kit of accessories to isodose curves gamma therapeutic units includes a device with disposable collimators forming round fields with 20, 30 and 40 mm diameters, an oblong field 20x30 mm and segmental field with axes 20x26 and 26x32 mm at a distance of 75 cm from a source. Dosimetric characterization of collimators was studied; dose fields formed by open beams using collimators were compared dosimetric characteristics