♦ Intracavity—radioactive material into body cavities

Uses—gynae cancers —bronchial cancers —oesophageal cancers —bile duct cancer

♦ Interstitial—radioactive material in tissues

Uses—breast cancer —tongue cancer —floor of mouth cancer —anal cancer

♦ Surface of tumour

Implants can be classified as manually inserted, after-loading, or remote after-loading. Manual insertion of radiation sources should be avoided if possible owing to the radiation hazards to operating staff and nurses. After-loading is when radioactive material is loaded into hollow needles, catheters, or applicators that have been inserted into the tumour area previously. Manipulation of these 'cold' applicators carries no radiation hazard to medical and nursing staff, so that time can safely be taken to ensure optimal source geometry.

After-loading with radioactive material can be manual or remote (using machines such as the Selectron, commonly used to treat gynaecological cancer). For remote after-loading stainless steel pellets containing, for example, caesium in glass, are moved pneumatically from a computer-controlled lead-lined safe into intrauterine and vaginal applicators. This completely eliminates irradiation of theatre and nursing staff.

Some remote after-loading devices work at a very high dose rate e.g. the Microselectron (high-intensity iridium sources) or the Cathetron (high-intensity cobalt sources) and treatment is over in a matter of minutes.

Most implants are of the removable type—the radiation sources are removed after the delivery of the prescribed treatment dose. However, permanent implantations can be performed using relatively short half-life isotopes such as 125I or 198Au, which are implanted into the tumours in the form of seeds which remain after the radiation has decayed virtually completely.

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