For many years we have known that radiation and radioactivity can seriously harm health and even kill. Yet in controlled doses, and when concentrated on a specific site of the body, radiation can also cure or bring temporary relief. The trick is to kill the diseased cells or tissues without doing too much harm to normal body organs.
When radiation beams such as X-rays are used to treat a person, that treatment is called radiotherapy. About one person in ten, including children, receive radiotherapy at some time during their lives.
How does radiotherapy work?
Radiation beams cause damaging chemical changes in the nucleus – which is the control centre – of a living cell. This means that genetic damage occurs and the cell usually dies when it attempts to divide to form two new cells. Radiotherapy is used mainly for malignant tumours (cancers) with the aim of killing the harmful, cancerous cells as they attempt to proliferate. Radiotherapy is also used for other conditions unrelated to cancer such as overactivity of the thyroid gland (thyrotoxicosis), some skin rashes, rare forms of arthritis and to prevent excessive scarring.
Different forms of radiotherapy
External beam therapy uses radiation beams originating from a source outside the patient, often one metre or so away. The beam is carefully aimed at, and focused to maximum intensity on, a target area within the patient. Usually the patient lies flat and treatment takes a few minutes each day. This is the commonest form of radiotherapy in general use. There are several types of external beam X-rays produced from electrically operated machines. The type of X-ray depends on the voltage used in the machine. When extremely high voltages are employed, as in larger machines such as the linear accelerator which operates at between 4 and 20 million volts (megavolts), the beams are so energetic that they pass through skin and affect deeper tissues. These treatments are called high-voltage or megavolt-age radiotherapy and belong to a group called X-ray therapy. (X-rays were discovered by W.C. Rontgen in 1895.)
When smaller X-ray machines are used at lower voltages the beams are not so energetic and do not penetrate tissues so deeply. They are also located much nearer the patient. Such beams are used for treating disorders of skin and the tissues near the body surface. These treatments are called superficial, orthovoltage or low voltage radiotherapy and also belong to X-ray therapy.
The radioactive form of metal cobalt emits gamma rays which are similar to high-energy X-rays produced at voltages of one to two million volts. The cobalt source is usually 80 to 100 centimetres away from the patient and can rotate to any position. Implant treatments
For this form of radiotherapy, radioactive iridium wires or small radioactive gold pellets are inserted into tissues, following a local or general anaesthetic.
The implants expose the surrounding tissues to radiation. Wires are removed after a few days but gold pellets are left in because they soon become inert and harmless.
This technique is similar to the implant procedure above. Small radioactive sources are placed in a specially-made applicator which, under a general anaesthetic, is fitted securely within a hollow organ or natural cavity in the body. The uterus, vagina and anus can be treated in this way.
In this technique radiation is provided by a radioactive liquid, given to the patient in the form of a drink or injection. Radioactive iodine given in one of these ways can effectively destroy a diseased thyroid gland without the need for difficult surgery. Marie Curie (1867-1934) received the Nobel Prize twice (1903 for physics, and in 1911 for chemistry) in recognition of her discovery of polonium and radium and for her research on radioactivity. Her work pioneered the way for the treatment of some cancers.
Modern radiation equipment is quick and efficient and does not look threatening. The shaft of rays from this linear accelerator can reach the patient from different directions (for example, the shaft can turn through 360° as well as a combination of other movements).
Tissues containing rapidly dividing cells are also disturbed. The skin can become red and blistered above certain doses, especially when low voltage X-rays are used. Temporary hair loss may occur but only in the areas where the beams are aimed. Diarrhoea and sickness can follow treatment of large areas of the abdomen. A fall in the numbers of circulating red blood cells, white blood cells and platelets may also occur, especially when large parts of the skeleton, which contains the bone marrow that makes blood cells, are treated.
Sometimes side-effects can occur many years after radiotherapy. Examples are thinning of the skin and cataracts in the lens of the eye.
In modern radiotherapy everything possible is done to minimize these side-effects. The dosage of treatment given is carefully selected, with the aid of computers, for each patient. Medicines may be prescribed to reverse some inevitable side-effects. Many younger patients can continue their normal work or routine while having daily radiotherapy, which may go on for as long as six weeks. For others, including the very ill, it is necessary to stay in hospital.
The effects of radiotherapy
Because radiation beams do not directly affect the senses, people feel nothing when they receive the treatment. However, patients can experience abnormal side-effects following their treatment. The side-effects depend on which parts of the body are treated, to what extent, and for how long. Radiation is not capable of differentiating between healthy and disordered tissue. Because radiation has most effect on the cells in fast-dividing tissues, the normal, healthy body
Diseases treated by radiation
Radiotherapy can now cure around 90 per cent of small cancers in the skin, vocal cords and uterus, and it plays an important role in the cure of other cancers together with surgery and chemotherapy. Even when complete cure is not possible, radiation can provide palliative effects such as relief of pain, control of bleeding, reduction in coughing, and less difficulty in swallowing as a result of inoperable tumours that affect the normal function of the esophagus.