Radiotherapy is another 19th-century technology still going strong in the 21st century. Roentgen made the key observations underpinning modern radiotherapy in 1895 when he observed that invisible rays (which he called X-rays’) were produced when electrons were fired at a target in a vacuum – revealed by their ability to blacken photographic film. It was rapidly realized that X-rays were transmitting energy and that this energy could be potentially focused for treatment as well as imaging. Within a matter of months, the first patients, with skin tumours, were treated, a breathtaking rate of innovation. The technologies of both imaging and therapy have gradually been refined and improved over the last century or so, and now form key components of modern cancer therapy. Indeed, as already noted, the most effective parts of modern cancer therapy remain surgery and radiotherapy, with the additional gain from drug treatment in terms of cure rates being relatively marginal. In wealthy first-world economies, drug treatments can clearly be funded over and above these two key planks of therapy. However, in poorer countries, where difficult choices have to be made, very few drugs offer good value for money in curative terms compared to surgery and radiotherapy.
After the initial observations of the effects of X-rays, either electrically generated or produced by using radioactive isotopes, the technology has been progressively refined. Initial technology based on the vacuum tubes described by Roentgen in the 19th century gave a beam which could penetrate to internal organs but which deposited considerably more of the dose nearer the skin. In the 1950s, much more powerful, so-called mega-voltage machines became available. These were based on the artificial isotope Cobalt-60, now superseded by an electrically based device called a linear accelerator, usually abbreviated to linac. These latter machines used the magnetron valve developed in the Second World War for radar. The pulsed energy can be used to ‘shove’ electrons into the target at much higher energies with much better properties for treating deep-seated tumours – a sort of electronic ploughshare from a high-tech sword.
Modern radiotherapy can be very precisely targeted by integrating treatment delivery with detailed imaging. Side effects arise in two ways. In structures such as skin, gut lining, and the mouth, the effects can be likened to sunburn, with severity depending on the dose received. Effects experienced depend on the site treated and may include diarrhoea with lower bowel treatment, or sore mouth, hair loss, and reddening in treated skin, and so on. The second group of side effects is experienced in solid structures such as lung and kidney. In these organs, there is little immediate effect, but if critical dose constraints are exceeded, the irradiated tissue will progressively fail. Dose to critical organs adjacent to the target tumour is thus a key restriction on the delivery of radiotherapy – a certain amount of toxicity will be worth accepting in order to treat the cancer, but clearly, there comes a point when the damage may outweigh the benefit. Improved radiotherapy such as intensity-modulated radiotherapy (IMRT), involving very sophisticated dose distributions which appear to ‘bend’ dose around critical structures, is increasingly becoming available but increases costs and complexity of delivery. A linked development is on-board imaging in treatment machines which can be used to give image-guided radiotherapy (IGRT) where the treatment tracks movements in the tumour from day to day. The combination of IMRT and IGRT has the potential to both increase tumour control (by ensuring treatment is on target) and decrease side effects by better sparing of uninvolved tissues.