What is brachytherapy?
Brachy comes from the Greek root meaning short. Brachytherapy means that the radiation travels a short distance into the tissues, whereas with an external beam source the radiation must travel a long distance to reach its target tissue. In essence with brachytherapy the source of radiation is implanted directly into the tissue to be irradiated.
The oncologist can vary certain parameters:
· The dose of the radiation by changing the number of seeds used or by charging the seeds to a particular level of radiation.
· The energy delivered to the tissues by changing the radioactive material.
· The period of radiation by altering the radioactive isotope.
· The field of radiation by the particular placement of seeds.
· Different cancers respond to different forms of radiation treatment. Oncologists have learnt through trial and error what type of radiation is best for each particular cancer.
What types of brachytherapy are available for prostate cancer?
There are basically two forms of brachytherapy:
Low dose brachytherapy (LDR): Low dose brachytherapy is the conventional method whereby radioactive seeds are placed permanently into the prostate gland. In prostate cancers the commonest seeds used are radioactive iodine or palladium. These deliver a low dose of radiation over a period of several months. After a certain time, determined by the isotope, they become inactive. There has never been a report that these seeds can cause any harm over the long term. The method by which the seeds are placed is critical and will be discussed further on in the text.
High dose brachytherapy (HDR): This treatment is not commonly used. It is available only in certain academic institutions. In this form of treatment high dose iridium rods are temporarily placed in the prostate gland for a few minutes. The dose is repeated every six hours until four doses have been given. This form of treatment is used in patients who for some technical reason cannot have LDR therapy. Safety protocols are much more stringent because the radiation is more dangerous. Also the treatment is far more involved technically, requires expensive auxiliary equipment and additional trained personnel. The treatment takes longer and additional external beam radiotherapy has to be given as well.
How are the seeds placed?
Preplanning Technique: In the early nineties a technique to place seeds permanently in the prostate gland was developed. The patient would have the prostate gland imaged carefully prior to the seed placement procedure. The oncologist would then design a plan to place seeds in the prostate according to its dimensions. The seeds would be ordered and the patient would have his procedure about a week later. The patient went to theatre, was anaesthetised and the seeds then inserted through the perineal area into the prostate gland. However what was not well understood was the issue of prostate mobility. Needles were inserted into the prostate gland without direct visualisation of the gland. The needles were inserted according to the position of the gland on the pre-plan scan. Inserting needles into a prostate gland can change its shape and move it up to 20 mm in a headwise direction. The result was that needles were now not positioned correctly and the seeds were therefore placed in the wrong position. This led to damage to surrounding organs and cold zones within the prostate gland. Side-effects where thus common including serious side-effects. Cure rates were not excellent. Amazingly many centres continue to use this technology.
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