1 General Aspects

6 General Aspects

High Dose Rate (HDR) brachytherapy (Fig 1.8B and C) has been widely accepted over the past two decades, particularly for the treatment of gynaecological tumours and for tumours at other sites which are not easily accessible for Low Dose Rate (LDR) techniques because of the relatively larger size and lower strength of LDR sources. Most recently Pulsed Dose Rate (PDR) brachytherapy (Fig 1.9) has been developed. (12,18) PDR brachytherapy like HDR brachytherapy utilises a single miniaturised source which moves step by step through implanted afterloading devices to achieve the desired dose distribution. In PDR such a sequence of steps, also called a pulse, is repeated a number of times to obtain the prescribed total dose. By choosing an appropriate number of pulses one can simulate, from a radiobiological point of view, a continuous low dose rate treatment. This and other newly developed techniques allow brachytherapy to be used in a very wide variety of tumour types and sites. (32)

Fig 1.9: VariSource (Varian) More and more sophisticated treatment planning systems are used. They can be combined with modern image information; the dose distribution is more and more conformal to the PTV (Planning Target Volume). (2,20,32,34)

2

Brachytherapy Definitions

Brachytherapy consists of a very local irradiation. The dose is delivered by one or several sealed sources. Different kinds of brachytherapy have been defined: (13,14,15,16,17,19,34) 2.1 characterised by the positioning of the radionuclides: − interstitial brachytherapy: radioactive sources are inside the tumour − contact brachytherapy or plesiobrachytherapy: radioactive sources are close to the tumour. Contact brachytherapy is divided into four different kinds of brachytherapy: intracavitary, intraluminal, endovascular and surface brachytherapy.