Brachytherapy allows specific or complementary treatment of cancerous tumours, specifically in the ENT field, as well as of the skin, the breast or the genitals.

The main radionuclides used in brachytherapy, in the form of sealed sources, are caesium 137 and iridium 192, which have definitively replaced the radium 226 needles or tubes used in the first half of the 20th century. These two radionuclides have half-lives of 30 years and 74 days respectively.

Brachytherapy techniques involve three types of applications.

Low dose rate brachytherapy, requiring patient hospitalisation for several days, gives dose rates of 0.4 to 2 Gy/h. The iridium 192 sources are used for interstitial applications (inside the tissues). The sources generally come in the form of wires of 0.3 to 0.5 mm in diameter, with a maximum length of 14 cm and which linear activity is between 50 MBq/cm and 250 MBq/cm. Endocavity techniques (inside natural cavities) use either iridium 192 wires or caesium 137 sources. In both cases, the sources remain in place in the patient for the duration of hospitalisation.

Sources are implanted in two stages and at two different locations: in the application room, where source catheters are fitted into the patient and their correct positioning is checked by radiological filming, and then in a room specially reinforced for radiation protection reasons, in which the radioactive sources are implanted. With this technique, it is possible to use a source applicator, in particular for the caesium 137 sources, thereby optimising personnel protection.

Low dose rate brachytherapy requires a room for storage and preparation of the radioactive sources, a room for radiological location and application, and at least 2 protected rooms for hospitalisation of patients implanted with sources.

Room protection must be determined on the basis of a caesium 137 source of 8200 MBq or an iridium 192 source of 5600 MBq, placed in the centre of the patient's bed, which must be fixed in place.

In recent years, low dose rate brachytherapy techniques have been supplemented by the use of sealed sources of iodine 125 (half-life of 60 days) to treat prostate cancers. The iodine 125 sources, just a few millimetres long are permanently installed in the patient's prostate. Their unit activity is between 10 and 25 MBq and treatment requires about one hundred grains representing a total activity of 1500 MBq, delivering a prescribed dose of 145 Gy to the prostate.

Medium dose rate pulsed brachytherapy uses dose rates of 2 to 12 Gy/h delivered by iridium 192 sources of small dimensions (a few millimetres), with maximum activity limited to 18.5 GBq. Each source is applied with a specific source applicator. This technique delivers doses identical to those of low dose rate brachytherapy, and over the same period, but given the higher dose rates, irradiation is split up into several sequences (pulses). The patient does not therefore carry the sources permanently, which is more comfortable and enables him to receive visitors. This technique, which is likely to be increasingly used, significantly improves the radiation protection of the personnel, who can now work with the patient without being exposed, once the source has been returned to the applicator's storage container. This technique can only be carried out in units which already carry out low dose rate brachytherapy; the room(s) set aside for hospitalisation of patients for whom this technique is well suited must have reinforced radiological protection based on an iridium 192 source of 18.5 GBq.

High dose rate brachytherapy uses an iridium 192 source of small dimensions (a few millimetres) and maximum activity of 370 GBq delivering dose rates higher than 12 Gy/h. A source applicator comparable to that employed for pulsed brachytherapy is used. The treatment times are very short (no more than a few minutes), unlike the previous techniques. Irradiation is carried out in a room similar to an external radiotherapy room, with the same safety measures. High dose rate brachytherapy is primarily used to treat cancers of the oesophagus and bronchus.