What is brachytherapy ?
Brachytherapy is the treatment of cancer using radioactive sources which are placed near or within the tumour. When radioactive sources decay they emit X-rays that can be used to destroy tumor cells. The advantage of brachytherapy is that the dose is delivered directly to the tumour thereby reducing the dose to surrounding organs.
Brachytherapy is employed mainly as a treatment for gynaecological cancers where access to the tumour is easily obtained. This type of treatment is called intracavity brachytherapy and involves placing sources in the vaginal cavity, the cervix or the uterus.
Brachytherapy can also be employed in other anatomical sites that are readily accessible, such as the chest, the tongue, and the lip. This involves placing hollow needles through the tumour and loading the needles with radioactive wires sometime after the actual implant. This type of therapy is called interstitial therapy. It is possible to treat less accessible organs within the body using this technique but it requires fairly invasive surgery.
What sort of sources are used ?
In the early days of brachytherapy the only source that was
available to doctors was the naturally occuring radium. This was
fashioned into needles or tubes and encased in stainless steel or
platinum. After the invention of nuclear reactors artificial
radioisotopes could be manufactured by exposing stable elements
to a neutron beam. The neutrons are absorbed by the stable
nucleus of the atom forming an unstable, or radioactive, nucleus. This unstable
nucleus will decay at a later date to a more stable element. This
process made available caesium, cobalt and iridium isotopes
amongst others. These sources are much safer to handle than
radium and radium sources are now, in fact, obsolete.
How does brachytherapy work ?
The rapid fall-off of dose rate around a brachytherapy source
makes it difficult to specify a treatment dose to the tumor site.
Therefore, implantation and dosimetry systems are used to
prescribe the treatment. The two systems used at Cookridge are,
the Paris system for interstitial implants and the Manchester
system for intracavitary implants.