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Brachytherapy

Introduction

Brachytherapy involves the placement of radioactive sources in or near tissue, usually for the treatment of cancer. The sources can be placed on top of the tissue (surface or mould), in the tissue (interstitial), in a lumen (intraluminal), in a cavity (intracavitary). They can be used  during an operation (intraoperative) that involves surgical removal of diseased tissue with subsequent irradiation of tissues at risk, or in a blood vessel (intravascular) with the source being placed in or close to the lesion. Some sources could be left in for a specified length of time (temporary implants) while others are applied as a permanent implant. The sources could be loaded manually or using a remote control afterloading device. The irradiation could be given by high dose rate (HDR) or a low dose rate (LDR) sources.

Important Principles

Computerized treatment planning for brachytherapy is done by specialized systems designed for HDR treatments or using more generalized radiation treatment planning systems. Brachytherapy treatment planning always involves some form of source localization with respect to the tissues to be irradiated, either using 90 degree or oblique radiographs or using 3-D  image data sets. The dose calculation algorithms tend to be less sophisticated than those used for external beam planning since the geometrical dispersion of photons is the predominate cause of the shape of the dose distribution.

Introduction to References

Chapter 13 of the IAEA Handbook for Teachers and Students gives a good overview the physical and clinical aspects of brachytherapy. The report by the AAPM Task Group provides a brachytherapy code of practice.