In LDR brachytherapy, tiny radioactive particles the size of a grain of rice (see Figure 1) are implanted directly into the site of the tumour. These particles are known as 'seeds', and they can be inserted linked together as strands, or individually. Because the seeds are inserted or implanted directly into, or very close to, the tumour, they deliver high doses of radiation to the tumour without affecting the normal healthy tissues around it.