Dr Tim Squire Radiation oncologist and director of training at Townsville University Hospital, Queensland.

First published online on 19 April 2024

BACKGROUND

THE origin of radiotherapy began

with the discovery of X-rays in 1895. This makes radiotherapy one of the oldest forms of cancer therapy, second to surgery, there being evidence of the latter from about 3000 BC in archaeological studies. 1 Radiotherapy has evolved and advanced rapidly in recent times largely because of improvements in technology. 2D radiotherapy planning was used in the 1960s-70s and involved the radiation oncologist estimating the dose and distribution of radiation based on X-ray films( see figures 1A and 1B). 3D radiotherapy planning utilised the introduction of 3D data sets made available through the first CT scanner in 1970s-80s. This allowed radiation oncologists to prescribe the radiation dose more accurately to visualised soft tissue structures and avoid nearby normal structures( see figure 2). In the 1990s, intensity modulated radiation therapy( IMRT) began to be used. Here multiple small beams of radiation could be shaped by the treating machine to create an even more conformal dose distribution( see figure 3). More recently, volumetric modulated arc

therapy( VMAT) combined the principles of IMRT with the movement of the treatment machine around the patient, further improving conformality of treatment plans( see figure 4). VMAT combined with movement of the patient on the bed is known as tomotherapy.

Stereotactic radiotherapy is a form of external beam radiotherapy that delivers very high doses to small tumours. There is emerging evidence that this treatment technique may be particularly useful in treating early metastatic disease aggressively. 2

A further advancement in radiation therapy delivery is the MRI-linear accelerator that combines an MRI with the radiation treatment machine; this delivers radiotherapy with greater precision compared with conventional CT guidance. The first of these machines in Australia was installed at the Townsville University Hospital( see figure 5).

The previously mentioned treatment machines deliver radiation in the form of photons( X-rays) or electrons, depending on the clinical requirement. The Australian Bragg Centre in Adelaide will be the first facility in Australia to use protons as

a means of delivering radiation therapy. 3 This will likely benefit paediatric patients the most because of the improved radiation dose distribution compared with standard X-rays.

This How to Treat is a broad overview of what radiotherapy is, how it works and the management of common side effects. It aims to provide a basic understanding of radiotherapy and the process of the treatment, in order to aid GPs in advising patients on what to expect.

HOW IT WORKS

RADIOTHERAPY is the utilisation

of high energy X-rays( sometimes other types of radiation) to damage the DNA of cancer cells and destroy them. The aim of treatment varies over a spectrum, from complete eradication of the tumour at one end, to shrinkage to reduce symptoms in the palliative setting at the other.

The process of X-ray production involves a linear accelerator, which accelerates electrons almost to the speed of light into a dense target to generate X-rays. These X-rays can be shaped into position by small pieces of shielding material in the treatment head. If electrons are being utilised

for treatment, then the dense target is removed so that electrons then enter the patient to cause damage to the tumour.

Importantly, radiotherapy is a local treatment modality; this differs significantly from systemic therapies like chemotherapy, hormone therapy, immunotherapy or targeted therapy, as these therapies treat cancer throughout the body.

Very high energy X-rays have the ability to penetrate deeply and treat deep-seated tumours over a distance of many centimetres. If a tumour is more superficially located, such as a skin cancer, electrons may be used. This is because of the fundamental nature of electrons in that they are relatively light and have a negative charge. This means that when they are delivered, they do not penetrate deeply, which spares deeper tissues from a radiation dose.

Most radiotherapy is delivered externally into the patient, known as external beam radiotherapy. However, in some cases, internally inserted radiotherapy, known as brachytherapy, is used. Brachytherapy may be administered alone or in conjunction with external beam