7 - Radiotherapy: principles and applications

Summary

Introduction

The therapeutic use of radiation in gynaecological cancer quickly followed the discovery of X-rays by Roentgen in 1895 and radium by the Curies in 1898. The aim of radiotherapy is to destroy the cancer if possible without damaging the surrounding normal tissues. The application of a cancericidal dose of radiation to the cancer must be balanced against the inevitable collateral damage caused to local normal organs at risk. Radiotherapy treatment can involve a combination of external beam radiotherapy and brachytherapy. External radiotherapy (teletherapy) employs the use of a high-energy photon (X-ray) beam generated from a linear accelerator. Brachytherapy (Greek brachy, short) involves the use of sealed radiotherapy sources placed close to the treated tissue. The sources may be placed in the natural cavities of the vagina or uterus (intracavitary treatment) or needles or tubes inserted into the tissues (interstitial brachytherapy). The two modalities of external beam radiotherapy and brachytherapy can be combined or used individually.

Radiobiology

Radiotherapy uses the damaging effects of ionising radiation on cellular DNA. X-rays and, less commonly, gamma-rays are the commonly used forms of ionising radiation. The 'four Rs' form the basis of radiobiology: repair, repopulation, reoxygenation and redistribution.