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P C Shrimpton

Publications and source records attributed to P C Shrimpton.

At least 19 recordsLinked to original sources
PubMed2006

National survey of doses from CT in the UK: 2003.

A review of patient doses from CT examinations in the UK for 2003 has been conducted on the basis of data received from over a quarter of all UK scanners, of which 37% had multislice capability. Questionnaires were employed to collect scan details both for the standard protocols established at each scanner for 12 common types of CT examination on adults and children, and for samples of individual patients. This information was combined with published scanner-specific CT dose index (CTDI) coefficients to estimate values of the standard dose indices CTDI(w) and CTDI(vol) for each scan sequence. Knowledge of each scan length allowed assessment of the dose-length product (DLP) for each examination, from which effective doses were then estimated. When compared with a previous UK survey for 1991, wide variations were still apparent between CT centres in the doses for standard protocols. The mean UK doses for adult patients were in general lower by up to 50% than those for 1991, although doses were slightly higher for multislice (4+) (MSCT) relative to single slice (SSCT) scanners. Values of CTDI(vol) for MSCT were broadly similar to European survey data for 2001. The third quartile values of these dose distributions have been used to derive UK national reference doses for examinations on adults (separately for SSCT and MSCT) and children as initial tools for promoting patient protection. The survey has established the PREDICT (Patient Radiation Exposure and Dose in CT) database as a sustainable national resource for monitoring dose trends in CT through the ongoing collation of further survey data.

Adult↗
PubMed2002

Influence of patient age on normalized effective doses calculated for CT examinations.

Monte Carlo simulations of CT examinations have been performed to estimate effective doses, normalized to axial air kerma, for six mathematical phantoms representing ages from newborn to adult, and for three CT scanner models covering a range of designs. Organ doses were calculated for CT exposures of contiguous, 1 cm wide, transverse slices in each phantom and summed to give normalized effective doses for scans of four regions of the trunk and head. In all cases an inverse trend is observed between normalized effective dose and phantom age, with the dose to the newborn from head and neck scans being 2.2-2.5 times higher than that to the adult, depending on scanner model. Corresponding increases for scans of the trunk region are more variable between scanners and range from a factor of 1.3 to 2.4. If typical clinical exposure conditions for adults are also utilized for children, then, for example, the effective dose to the newborn from a chest scan could be above 15 mSv. It is concluded that CT has the potential to deliver significantly greater radiation doses to children than to adults and in view of their greater susceptibility to radiation effects, special efforts should be made in clinical practice to reduce doses to children by the use of size-specific scan protocols.

Adolescent↗
PubMed1999

Dosimetry for optimisation of patient protection in computed tomography.

The complex conditions of irradiation in computed tomography (CT), involving highly-collimated X-ray beams, necessitate the use of specially-defined dose descriptors such as the computed tomography dose index (CTDI). When used in a weighted form (CTDIW), this concept can describe the absorbed dose from a single slice in standard head and body phantoms. The model can easily be extended to characterise patient exposure for a complete examination by means of the reference dose quantity dose-length product (DLP). Effective dose can also be estimated from DLP, when required.

Humans↗
PubMed1999

Diagnostic medical exposures in the U.K.

Surveys in the U.K. have identified the patterns of patient exposure from diagnostic medical radiological procedures and have led to the development of structured advice to promote optimisation of patient protection, including diagnostic reference levels for some common conventional X-ray examinations. Trends for reductions in individual patient and collective doses from these particular procedures have been offset by increasing application of computed tomography. Practice in diagnostic nuclear medicine is conducted by authorized physicians on the basis of recommended maximum usual activities of radiopharmaceutical for specific procedures.

Data Collection↗
PubMed1988

A comparison of diagnostic radiology practice and patient exposure in Britain, France and Italy.

Surveys have been conducted in Britain, France and Italy, using essentially the same techniques, to establish the level of provision of diagnostic radiology services, the frequency of X-ray examinations and examples of the radiation doses delivered to patients in each country. Different national strategies for conducting some types of X-ray examination and marked differences in the general availability of this aspect of health care indicate that the justification and optimization of medical exposures is not interpreted in the same way in these countries.

Age Factors↗
PubMed1986

Doses to patients from routine diagnostic X-ray examinations in England.

A collaborative survey between the National Radiological Protection Board and the Hospital Physicists' Association has been conducted to ascertain current levels of exposure for patients undergoing 10 routine types of X-ray examination in England. The main part of this study consisted of measurements on nearly 3200 patients attending 20 randomly selected English hospitals. The energy imparted to each patient was determined from a measurement of the total exposure-area product for the examination. In addition, thermoluminescent dosemeters were attached to the patient's skin to enable the derivation of doses to the major radiosensitive organs, either directly or using appropriate conversion factors calculated for a mathematical phantom by a Monte Carlo technique. Histograms are presented showing the wide distributions often observed in the doses for each type of examination. Mean values of exposure-area product, energy imparted to the patient, entrance skin dose per film and organ dose are reported, together with coefficients of variation. Comparison of the results with those from similar surveys in the UK and abroad is complicated by inconsistencies in the reporting of such data, but substantial differences are sometimes apparent, particularly for the estimates of organ doses. The present measurements will provide a useful baseline for future measurements and will be used to evaluate the collective dose to the population from medical exposures and the radiation risks from the various radiological procedures.

Humans↗
PubMed1984

The measurement of energy imparted to patients during diagnostic x-ray examinations using the Diamentor exposure-area product meter.

The mean energy imparted to the patient has been proposed as a practical quantity which may be useful for assessing somatic risk in X-ray diagnostic radiology. A technique is described for estimating energy imparted during most common X-ray examinations of the trunk or complete head from a measurement of exposure-area product conveniently provided by the Diamentor transmission ionisation chamber. The necessary energy imparted calibration for the Diamentor has been deduced from consideration of incident spectral energy fluence and Monte Carlo calculations of the fraction of total beam energy imparted to mathematical phantoms representing the patient. The relationship between energy imparted and exposure-area product depends primarily on the applied potential and total filtration of the X-ray beam, and to a lesser extent on voltage waveform and X-ray target angle. Direct measurements of energy imparted to an Alderson Rando phantom for a range of irradiation conditions provided an excellent verification of the technique developed. Using the energy imparted per exposure-area product factors presented, overall uncertainties of less than +/- 15% and +/- 20% should be possible for measurements of energy imparted during examinations of the trunk and head respectively using the Diamentor.

Adult↗