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Radiotherapy -- the use of radiation in the treatment of disease -- is an effective weapon in the treatment of many forms of cancer. With the development of technical refinements it is becoming increasingly successful.

Radiotherapy spread is used to control the growth and spread of abnormal body cells. All living cells are damaged when they absorb energy from X-rays and gamma-rays but growing or dividing cells are damaged more easily than others. It is because cancer cells grow more rapidly than normal cells that they are slow to recover from the effects of radiation.

Radiation from X-rays and gamma-rays also destroys small blood vessels on which tumour cells depend for nourishment, so that following radiotherapy these cells are more susceptible to the body's own natural defences.

While surrounding normal tissue is more resistant to this type of radiation, it is still easily damaged. More than any other factor, damage to healthy tissue limits the doses of radiation used in treatment.

The many types of X-ray machines in everyday use differ in the amount of energy or power of the X-rays that they produce. If a tumour lies in or close to the skin it would be unwise to use high-energy X-rays that would penetrate deep into the body and damage normal tissues. Conversely, there is no point in using low-energy X-rays to treat a lung tumour, for example; the X-rays will not penetrate far enough.

So there are superficial voltage X-ray machines that are used to treat skin cancers, deep X-ray therapy units that are used to treat tumours up to a depth of 10cm (4in), and megavoltage or supervoltage machines that are used to treat deep-lying tumours.

Because it is difficult to produce very high-energy radiation from X-rays, gamma-ray sources are sometimes used for this purpose. Cobalt or caesium are the substances in most common use. A gamma-ray unit consists simply of a quantity of a radioactive isotope of caesium or cobalt encased in thick lead shielding. A small aperture in the shielding is opened during treatment, allowing a gamma-ray beam to emerge.

When powerful X-ray and gamma-ray beams are used it is essential to take great care to protect normal . tissue from exposure. The narrowest possible X-ray beam which will encompass the whole of the tumour is used.

Healthy areas are covered with lead shielding and when this is technically difficult - on an irregular surface such as the face, for example - a mould or mask is specially made to fit over the entire region, with a 'window' cut out over the area to be treated.

It is also possible to give radiotherapy by placing radioactive sources within the body. Needles, tubes, wires, or tiny seeds of radioactive material may be implanted in the tumour or placed in close contact. Because only low-energy sources are used, the radiation emitted has only limited penetration and normal tissues are unlikely to be damaged.

In the treatment of cancer of the cervix (neck of the womb) and of the uterus (womb) tiny radium sources are placed inside the upper part of the vagina and the uterus, giving a much higher dose of radiation than would be possible using other techniques.

The decision to begin radiotherapy treatment is usually taken by a team of doctors, after the alternatives have been fully discussed with the patient.

Treatment is planned by the radiotherapist in conjunction with a radiation physicist. Together they will map out the location of the tumour on an X-ray film or a scan of the diseased area. Using a special computer they will calculate precisely the energy, dosage and position of the treatment beams that will be required.

The beam positions, or 'fields', are marked on the patient's skin using indelible ink or sometimes tattoos. This permanent method of marking the skin is done so that the patient can be accurately re-positioned under the beam each time treatment is given.

Treatment is usually spread over three to six weeks with some three to five divided doses per week. The total dosage determines how many tumour cells are destroyed, but dividing the doses allows much better recovery of normal tissue and increases the total dose that can be tolerated.

Most patients can be treated as outpatients. The treatment is quite painless and involves lying or sitting quite still on an X-ray table beneath the radiation beam for a few minutes at a time, in a special room that has walls shielded with lead and concrete.

The staff who work in radiotherapy departments are at special risk from long-term effects of exposure to radiation and are therefore not allowed to remain in the room while treatment is being given. But the radiographer in charge always keeps a careful watch over the patient through a lead-glass window and is also able to talk to the patient throughout the period of treatment.

The most common side-effect of radiotherapy is redness and soreness of the skin overlying the treatment field. When this occurs, patients are instructed not to wash or shave affected skin for a few days until it improves, since soap and drying with a towel make the soreness much worse.

If the field includes an area of scalp the patient may lose some of his hair, but it will usually grow back after treatment has been completed.

Any exposure of the mouth, gullet, stomach or intestines may cause loss of appetite, dryness of the mouth, vomiting or diarrhoea. A high-calorie, easily assimilated diet is often necessary until these effects wear off. Blood counts taken during treatment are used to monitor harmful effects or radiation of the bone marrow. Radiation sickness is generally treated with anti-nausea drugs and sedation.

A few types of cancer are highly sensitive to radiotherapy, especially some tumours of the lymph glands and tumours of the testes. Complete disappearance of tumours can be expected within the treatment area, and complete cure is often achieved by radiotherapy. Skin cancers are less sensitive but will usually disappear completely following treatment. Less sensitive still are the tumours that can occur in the bladder, uterus, ovary, lung and breast.

Radiotherapy may be used after surgery, just in case any tumour cells have been left behind. In lung cancer, complete disappearance of the tumour following radiotherapy is possible, but spread usually takes place at such an early stage and to so many different parts of the body that curative treatment with radiotherapy is not usually possible, although it can relieve some of the symptoms and the pain that are caused by the cancer.


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