The dosimetry requirements for healthcare range from levels experienced in diagnostic examinations to those necessary for cancer treatment by radiotherapy.

Radiotherapy

(Image courtesy of Elekta)

Every year 200,000 people are diagnosed with cancer in England, and are treated with radiotherapy, chemotherapy and surgery. Radiotherapy treatment is given to about half of all patients, with intent to cure the cancer or to alleviate suffering. The radiation may be given in the form of external beam radiotherapy using high-energy electrons or X-rays, or it may come from radioactive sources placed inside the patient (brachytherapy, nuclear medicine). For radiotherapy to effect a cure, it is essential that the correct amount of radiation (absorbed dose) be delivered to the patient. Too small a dose, and one or more cancerous cells may survive, leading to recurrence of the disease. Too large a dose, and the healthy tissue surrounding the tumour may be destroyed. Optimal treatment of, for example, some head and neck tumours, requires that the dose delivered should be within only a few percent of that prescribed.

Every treatment is monitored with instruments whose calibration can be traced back, via accurate secondary standard dosemeters, to the primary standard instruments held at national standards laboratories such as NPL. These standards measure absorbed dose or air kerma directly from first principles, and are subject to regular comparisons with other national standards worldwide. Reference instruments are calibrated against these primary standards in order to allow the determination of absorbed dose by following the relevant Codes of Practice recommended, in the UK, by the Institute of Physics and Engineering in Medicine. Accurate dosimetry is essential to maintain and improve radiotherapy and ultimately to improve cancer survival rates.

Diagnostic Radiation

Within the UK over 40 million diagnostic X-ray examinations take place and approximately 450,000 patients receive radionuclides for diagnostic purposes each year. In diagnostic procedures, the radiation dose received by the patient is an unwanted side effect and always to be minimised, subject to acceptable image quality being achieved. There is considerable evidence that the doses received by patients for a given examination can vary considerably from clinic to clinic, however the Ionising Radiation (Medical Exposure) Regulations, IR(ME)R, introduced in May 2000, require a dose reference level to be set for each procedure in every clinic and a demonstration of consistent dosimetry.

As part of the infrastructure for compliance with these regulations NPL set up a calibration service for diagnostic X-ray dosemeters. These calibrations are carried out at present on constant potential industrial sets that are different to clinical sets used in hospitals. Our diagnostic facility is equipped with two clinical X-ray machines: a 40 to 150 kV diagnostic unit and a 20 to 35 kV mammographic unit. The new sets are high frequency X-ray machines typical of the type used in hospitals and clinics for general diagnostic and mammographic X- ray examinations, and are used for the calibration of kVp meters in qualities typical of those used in hospitals and clinics. This enables NPL to offer a calibration service more suited to the requirements of the medical community, helping to reduce the doses received by patients across the UK.

The safe and successful use of radionuclides for medical diagnosis depends critically on accurate measurement of the activity administered to the patient. In order that radiation doses to everybody concerned are kept to levels which are as low as reasonably practicable whilst still ensuring that diagnosis is effective, it is important that the activity of the administrations are known to a reasonable degree of accuracy. It is important too that those activity measurements can be made quickly and be shown to be traceable to national and international measurement standards. The instrument of choice for these measurements is a radionuclide calibrator, the main component of which is an ionisation chamber. In most cases activity measurements are made in hospitals using a relatively simple device called an ionisation chamber. All such devices in UK hospitals are calibrated using reference materials or other standards from NPL, which in turn have been calibrated against NPL's primary standards of activity. Ionisation chambers provide extremely reliable, efficient and economic measurement standards to the medical community.

Nuclear Medicine

The safe and successful use of radionuclides for medical diagnosis depends critically on accurate measurement of the activity administered to the patient.

In order that radiation doses to everybody concerned are kept to levels which are as low as reasonably practicable whilst still ensuring that diagnosis is effective, it is important that the activity of the administrations are known to a reasonable degree of accuracy. It is important too that those activity measurements can be made quickly and be shown to be traceable to national and international measurement standards.

The instrument of choice for these measurements is a radionuclide calibrator, the main component of which is an ionisation chamber. In most cases, activity measurements are made in hospitals using a relatively simple device called an 'ionisation chamber'. All such devices in UK hospitals are calibrated using reference materials or other standards from NPL, which, in turn, have been calibrated against NPL's primary standards of activity. Ionisation chambers provide extremely reliable, efficient and economic measurement standards to the medical community.