Radiotherapy
In radiotherapy doses of radiation many thousands of times higher than those used in diagnostic radiology are used to treat cancers. The aim is to cure the cancer or at least to alleviate the most distressing symptoms. For a cure, sufficiently high doses must be delivered to kill all the living cells within the tumour and this will inevitably cause some damage to surrounding healthy tissues. Modern radiotherapy techniques are designed to reduce the amount of such damage to a minimum.
In external beam therapy a beam of x-rays, gamma rays or electrons from an accelerator is directed at the tumour. The beam is tightly collimated and is rotated around the patient so that it irradiates the tumour from many different directions and so does not continuously pass through the same healthy tissues. Also to help reduce possible side-effects, the dose is delivered in many small fractions over a period of days or weeks.
In brachytherapy, sealed radioactive sources in the form of small wires or rods are surgically inserted into the tumour to produce a highly localised dose to destroy it. Alternatively, unsealed radioactive material in a form that is selectively absorbed by a specific tissue or organ may be given to the patient, in a therapeutic variant of nuclear medicine. For example, radioactive iodine may be swallowed to treat cancer of the thyroid.
Radiation doses of many tens of gray are needed to kill the cancer cells effectively. Great care is required to deliver accurate doses since doses that are too low or too high may lead to incomplete treatment or unacceptable side-effects. Radiotherapy is consequently only used when the outlook for a cure for a life-threatening disease or for relief from unbearable pain is good and when other methods of treatment would be less effective. In these circumstances, radiological protection against the possible long-term effects of radiotherapy exposures is of less importance and NRPB has no current plans for studies in this area.
