Brachytherapy is a descriptive term for a particular delivery of radiation treatment, and the term can be applied to almost any part of the body. Brachytherapy is not a new form of treatment; it was first used for prostate cancer around 1910. With modern computers and imaging however, the current method of delivery of radiation to the prostate is about as far from that as an Airbus jet is from a steam train.

Brachytherapy is a word derived from the Greek word "brachy", meaning close up, or near, and with the "therapy" attached the word can translate to "close treatment". The object of brachytherapy is to deliver a dose of radiation to as small a volume as appropriate or possible. Brachytherapy utilises a basic principle of physics called "the inverse square law" where the dose of radiation falls away much faster when the source of the radiation is close than when the source is further away (as with external beam treatment).

This results in a rapid falloff in dose when the source is adjacent to, or within, the target volume. This technique permits an increased dose of radiation to the target region, and at the same time limits the dose of radiation to surrounding tissue or organs to a lower level. Being able to do this allows a choice of either increasing the dose to the target (and so have better local control) or lowering the dose to adjacent tissues or organs (and so have fewer side-effects).

In many cases both of these goals are achieved. Coupled with the newer methods and equipment for delivering external beam radiotherapy with "conformal techniques" there have been significant advances in the standards of delivery of radiotherapy for prostate cancer in the last 10 years.

Plain X-ray imaging shows the position of the needles but only in relation to bony anatomy, hence the need for CT and ultrasound imaging too.	A grid is used to place the needles into the prostate.

There are two different ways of delivering a brachytherapy treatment. Both involve implanting the radioactive sources into or adjacent to the prostate and so both are often termed "implants" (but they should not be confused with hormone injections which are also called implants). One technique involves placing the radioactive sources in the prostate and leaving them there for the patients’ life-time; the other places the sources into the prostate for a few days (currently only 36 hours). These are consequently respectively called ‘permanent’- or ‘temporary’- brachytherapy implants.

Current belief is that a permanent brachytherapy implant for prostate cancer is only appropriate for small or less aggressive cancers. The criteria set are a PSA less than 10, a Gleason score below 7 and a relatively normal gland. This is because the radioactive iodine used (I-125) in the seeds takes 8-12 months to deliver the radioactive dose and so a more aggressive or larger cancer might grow through the dose delivery and thus fail treatment. Because the temporary implant delivers a similar dose in only 36 hours, this is much less of an issue, and consequently there are no such restrictions on the use of a temporary brachytherapy implant.

A major advantage to an iodine seed implant is the rapidity of the treatment. With the insertion of 80-120 radioactive iodine seeds in about one hour, a patient need not have a course of treatment lasting seven weeks. However, current techniques have the potential to have the seed distribution in a less than ideal placement.

These can be controlled more accurately with a temporary implant, but routinely required with a temporary implant is 5-6 weeks of external beam as well, and this additional time can be inconvenient.

The issues with control of placement arise because of a combination of different reasons, one of which is visibility and certainty of placement of the implant.

Another is a "knock-on" effect where if one seed or needle is out of alignment, then others may well follow on too. An Integrated Brachytherapy Unit is an operating suite that is specifically designed to help minimise many of the issues that currently impact upon the delivery of these needles.

This new machinery will allow much more accurate placement of brachytherapy sources, both temporary and permanent, because it is specifically designed for its purpose. With X-ray and ultrasound imaging directly fed into a planning computer, the position of seeds or needles can be accounted for with "realtime planning" which allows for forward adjustment of the next needle placement depending upon the placement of the previous needle.

This then means that rather than having a static plan pre-prepared and not being able to accurately manage contingencies, one can work from a preprepared plan and also accurately alter it as and when required so that the final placement of the implant is still considered an ideal distribution.

In experimental work underway elsewhere in the world, the use of heat with microwave application is under considerable scrutiny, and with the use of an IBU it may also be possible to explore the addition of microwave/heat treatments in tandem with a brachytherapy implant.

This is still a little way off, but may well bring in very exciting results.

In summary then, we have new ways of delivering doses of radiation to the prostate that permit more accurate placement, and higher dose application that is resulting in better long-term control and with fewer side-effects than previously. We may also see that current equipment will allow other methods of treatment delivery in the foreseeable future.

Dr Michael A Izard

(Dr Izard is a Radiation Oncologist at the Mater Hospital, North Sydney. He has a special interest in prostate cancer and has been involved in brachytherapy for over 7 years).

Dr Katelaris has been performing Brachytherapy with Dr Izard for seven years, this multi-disciplinary co-operation is best for patient care