ABSTRACT
As well as its physical advantages, there are also biological advantages. Low dose rate (LDR) brachytherapy is a type of extreme hyperfractionation and is therefore relatively sparing to normal tissues. The dose rate may be low but it is delivered continuously, which shortens overall treatment time and reduces the opportunity for tumour repopulation during treatment. Conversely, high dose rate (HDR) brachytherapy must be fractionated to avoid normal tissue morbidity. Three dose rate bands are defined: LDR (1 Gy/h), medium dose rate (MDR) (1 to 12 Gy/h) and HDR (12 Gy/h). It is important to remember that if the dose rate is increased, a dose reduction is needed to give a biologically isoeffective dose. When changing from low to medium dose rate (e.g. changing from LDR intracavitary brachytherapy to MDR), a dose correction of approximately minus 15 per cent is needed. Other advantages of brachytherapy include the accurate localisation and immobilisation of the tumour, which removes the problems of organ movement and set-up errors seen with external beam radiotherapy (EBRT).
