CHAPTER ONE
INTRODUCTION 1.1
Background
Brachytherapy is a term used to describe the short distance treatment of cancer with radiation from small, encapsulated radionuclide sources. This type of treatment is given by placing sources directly into or near the volume to be treated. The dose is then delivered continuously, either over a short period of time (temporary implants) or over the lifetime of the source to a complete decay (permanent implants). Most common brachytherapy sources emit photons; however, in a few specialized situations beta or neutron emitting sources are used. There are generally two main types of brachytherapy treatment; intracavitary in which the sources are placed in body cavities close to the tumor volume and interstitial, in which the sources are implanted within the tumor volume (Podgorsak et al., 2005). There are also two types of brachytherapy that are used in the treatment of prostate cancer: permanent low dose radiation (LDR) and temporary high dose radiation (HDR). LDR brachytherapy uses iodine-125 and palladium-103 stored in titanium cases usually referred to as brachytherapy seeds. As the name permanent brachytherapy suggests, the seeds are permanently left inside the prostate gland. Over the course of their radioactive lives, the seeds will continuously emit low radiations until they decay completely. HDR brachytherapy uses a single radioactive seed made of iridium-194 which is sometimes referred to as an iridium wire. Soft flexible plastic catheters are inserted through the perineum and into the prostate gland. HDR brachytherapy entails an overnight stay in the hospital during which a patient undergoes two or three treatments with the wire through each catheter. In LDR brachytherapy, tiny radioactive particles each of the size 3.8 x 0.5 mm2 are implanted 2 directly into the site of the tumour. These particles are known as ‗seeds‘, and they can be inserted linked together as strands, or individually into the prostate. Because the seeds are inserted or implanted directly into, or very close to, the tumour, they deliver high doses of radiation to the tumour with minimum effect to the normal healthy tissues around it. This means that the procedure is less damaging than conventional radiation therapy where the radioactive beam irradiates other organs (Khan, 2003; Podgorsak et al., 2005).