[Formation of small fields using tele-gamma therapy devices].

Radiotherapy of certain tumor sites requires small-size fields of irradiation (less than or equal to 4 cm) with a good dose plateau and a sharp dose gradient on the field border. For this purpose a kit of accessories to beta-beam units includes a device with disposable collimators forming round fields with 20, 30 and 40 mm diameters, an oblong field 20 X 30 mm and segmental fields with axes 20 X 26 and 26 X 32 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.