Radiation dosimetry for diagnostic medical exposures

The number and complexity of medical procedures using X rays or radioactive materials are both steadily increasing. As a result, the dose from medical exposures now makes up the largest component of the radiation dose to the population in some developed countries. Key developments include the change from film to digital radiography, the increasing sophistication of interventional radiology allowing more complex procedures and the speed and facilities available with multi-slice computed tomography scanners that have extended the range of applications. It is crucial to have accurate dosimetry to monitor the impact of these developments, to ensure that techniques are optimised, and to provide information on health risk that clinicians can consider when justifying exposures. There are two aspects to dosimetry in radiology, assessment of doses to patients and measurement of equipment performance. The techniques that are used will be described, factors that influence doses and that must be considered when making measurements will be discussed, and future developments will be considered.     

Patient dosimetry in paediatric diagnostic radiology

A study of patient exposure in paediatric diagnostic radiology was conducted in three dedicated paediatric departments. The entrance surface dose was assessed by three methods: direct measurement by thermoluminescent dosemeters, calculation from the dose-area product and from the tube output. The results obtained by the these methods were compared, proving that all of them are applicable for the assessment of paediatric doses. Subsequently, the accumulated data were compared with the mean values from other similar studies and to the reference dose levels set by the Commission of European Communities, which clearly demonstrated the need for further investigation of the paediatric dose levels in Bulgaria and for optimisation of the radiological practice.     

New ethical issues for radiation protection in diagnostic radiology

The ethical basis for many medical practices has been challenged over the last two decades. Radiology has seen enormous growth during the same period. Many practices and equipment types, now commonplace, did not exist a generation ago. Yet the fundamental ethical basis for these practices has not seen a corresponding level of development. This is possibly an oversight, and may be particularly important given that these innovations have taken place over a period of changing social attitudes. Areas of concern include, for example, issues around justification, consent/authorisation, inadvertent irradiation of the foetus/embryo during pregnancy and the place of paternalism/individual autonomy in the structure of practice. This paper provides the background to a workshop on these issues held in late-2006 and presents a summary of its findings.     

The ICRU (International Commission on Radiation Units and Measurements): its contribution to dosimetry in diagnostic and interventional radiology

The ICRU (International Commission on Radiation Units and Measurements was created to develop a coherent system of quantities and units, universally accepted in all fields where ionizing radiation is used. Although the accuracy of dose or kerma may be low for most radiological applications, the quantity which is measured must be clearly specified. Radiological dosimetry instruments are generally calibrated free-in-air in terms of air kerma. However, to estimate the probability of harm at low dose, the mean absorbed dose for organs is used. In contrast, at high doses, the likelihood of harm is related to the absorbed dose at the site receiving the highest dose. Therefore, to assess the risk of deterministic and stochastic effects, a detailed knowledge of absorbed dose distribution, organ doses, patient age and gender is required. For interventional radiology, where the avoidance of deterministic effects becomes important, dose conversion coefficients are generally not yet developed.     

System for personal dosimetry in interventional radiology

The progress made in radiological image processing and transmission is being widely applied in new branches of medicine. The increasing use of interventional radiology in research and clinical practice means that new groups of workers are being exposed to radiation and need to be covered by a system of radiation protection. Interventional radiology requires the operator and assisting personnel to remain close to the patient; typically these procedures require placement of the hands within the radiation field. A system of hand dose monitoring was introduced in Poland in 2000. This system uses ring badges with TL dosemeters. The measurements conducted so far characteristically show an asymmetric right-sided distribution of monthly doses. As expected, operators and their assistants are the most exposed groups of medical personnel. Average hand doses may be very dependent on the type of procedure, personal skills and quality of equipment. The hand doses of these personnel are significant from a radiological protection point of view.     

Patient dosimetry in diagnostic and interventional radiology: a practical approach using trigger levels

Patient dosimetry is performed in radiology and interventional radiology to assess whether deterministic injuries may occur and to establish the risk of stochastic effects. A fundamental problem for patient dosimetry is that no single quantity can be used to accurately assess both the risk of stochastic effects and whether deterministic injuries will occur following a specific examination or procedure. In cardiology and interventional radiology, two different approaches to patient dosimetry are commonly used. Effective dose is a quantity which correlates reasonably well with the risk of stochastic effects. Effective dose may be deduced from the dose-area product (DAP) for the procedure if sufficient information is known. DAP does not correlate with maximum skin dose, which may be used to predict whether deterministic injuries may occur. DAP meter readings may be used as a trigger level for the investigation of maximum skin entrance dose. Trigger levels for different procedures are proposed.     

Staff dosimetry protocols in interventional radiology

Assessment of effective dose (E) for workers performing interventional radiology is particularly problematic due to the conditions of partial body exposure, so very few estimates of E are found in the literature. Two simple algorithms (the Rosenstein-Webster and the Niklason algorithms) are available that combine the readings of two dosemeters, one worn under the protective apron and one on the neck outside the apron, to estimate E for the range of imaging conditions typical of medical fluoroscopy. The algorithms are reviewed and their suitability for estimating E for personnel performing interventional radiology is analysed by comparison with the most recent experimental data. It can be concluded that the Niklason algorithm's estimates are in better agreement with the experimental assessments of E.     

Biological and physical dosimetry for radiation protection

In the 5^th Framework Programme (5FP) of the European Commission(EC), the European Late Effects Project Group (EULEP) and theEuropean Radiation Dosimetry Group (EURADOS) were funded toco-ordinate research in radiation protection based on theirwell-established experience. This was termed ‘clustering’and was intended to encompass research funded by National Agenciesand that funded directly by     

Radiation dosimetry by potassium feldspar

The thermoluminescence (TL) properties of raw and annealed feldspar have been studied for their use in gamma dosimetry. The raw gamma exposed feldspar shows glow peaks at 120°C and 319°C. Gamma dose beyond 500 cGy can be measured without any significant fading even after 40 days of termination of exposure. The annealed feldspar shows a glow peak at 120°C after gamma exposure. This peak can be used to measure gamma doses beyond 25 cGy when the TL is measured after 24 h from termination of exposure.     

Patient dosimetry protocols in digital and interventional radiology

Dosimetry requirements and protocols for performing measurements in digital and interventional radiology are discussed. Calculated entrance surface dose (ESD) is predicted to be of increasing interest in the future, replacing direct measurement with thermoluminescence (TL) dosemeters. The quantities proposed for establishment of reference values for interventional radiology are reviewed briefly, and the methods of collecting the data required for estimation of their values by means of traditional manual and new automatic methods are compared. It is concluded that the manufacturers of X ray units can largely solve the dosimetry problems of interventional radiology in machines with fully digital control systems after they have received sufficient data on patient dosimetry requirements.     

Patient and staff dosimetry problems in interventional radiology

Interventional radiology has developed into a dynamic part of radiology over the past twenty years, combining diagnostic and therapeutic methods. On the other hand, it is associated with high radiation doses to patient and staff, due to extended fluoroscopy times and the large number of radiographs. Also, occupational exposures from interventional radiology procedures have a tendency to be greater than other radiological examinations. The need for measuring and evaluating patient and staff doses is apparent. However, dose estimations depend on a large number of factors making these procedures very complex. The aim of this study is to review all the different approaches that appear in the literature on this matter, to delineate the different dosimetry protocols that are proposed and to focus on the practical problems that arise when an evaluation or comparison of dosimetry results is attempted.     

Calibration measurements and standards for radiation protection dosimetry

The safe use of ionising radiation for applications in medicine, electric power production and industrial processes requires accurate measurements that are traceable to national standards. Radiological calibration laboratories provide measurements that may be used to determine the calibration coefficients for personal dosemeters and survey meters. The wide range of ionising radiation applications results in the need for a wide range of reference radiation types and intensities to be available in the calibration laboratory. The methods used and the problems encountered while developing reference radiations are discussed.     

Comparison of double dosimetry algorithms for estimating the effective dose in occupational dosimetry of interventional radiology staff

'Double dosimetry' i.e. measurement with two dosemeters, one located above the protective apron and one under has been recommended in interventional radiology (IR) to determine the effective dose to staff. Several algorithms have been developed to calculate the effective dose from the readings of the two dosemeters, but there is no international consensus on what is the best algorithm. In this work, a few of the most recently developed algorithms have been tested in typical IR conditions. The effective dose and personnel dosemeter readings were obtained experimentally by using thermoluminescent dosemeters in and on a Rando-Alderson phantom provided with a lead apron. In addition, the effective dose and personnel dosemeter readings were calculated by the Monte Carlo method for the same irradiation geometry. The results suggest that most of the algorithms overestimate effective dose in the selected IR conditions, but there is also a risk of underestimation by using the least conservative algorithms. Two of the algorithms seem to comply best with the chosen criteria of performance, i.e. no underestimation, minimum overestimation and close estimation of effective dose in typical IR conditions. However, it might not be justified to generalise the results. It is recommended that whenever personnel doses approach or exceed the dose limit, IR conditions should be further investigated and the possibility of over- or under-estimation of effective dose by the algorithm used should be considered.     

Review of dosimetry instrumentation in digital and interventional radiology

Some dosimetry instruments and products are reviewed, the main emphasis being on patient dosimetry, recommendations for accuracy in different measurement applications and the results of some intercomparisons. It seems to be a common problem that the users of the general purpose air kerma (Ka) meters, dose-area product (DAP) meters or products such as thermoluminescence (TL) dosemeters are not always able to select the correct ionisation chamber, the calibration factor of a DAP meter or the TL dosemeter material and type, respectively, for different radiation conditions. The combined DAP and Ka meters developed recently, as well as the exposure data acquisition systems designed for monitoring one or more quantities or for determining the effective dose of a complicated examination, are described briefly. The most advanced software of these systems is able to display the dose distributions for the most exposed areas of the skin, on-line.     

Patient dosimetry measurements in 50 radiology departments in Belgium

Since July 2001, the Belgian law requires a yearly quality control measurement on all medical radiological equipment. The medical physicists of the AV Controlatom are certified experts in Belgium and perform these quality control measurements, including a patient dosimetry study. In this study, patient dosimetry results since January 2002 are presented for the following examinations: chest PA and LAT, abdomen and pelvis. Since conventional film-based imaging is currently being replaced by phosphorplate technology, a comparison between both technologies is made. In some radiology departments, digital imaging is already in use. These dosimetry results are also analysed. Dose reductions of >70% can be achieved. For the chest examinations, several departments still use fluoroscopy for positioning the patient. Results show that about half of the patient dose is due to the fluoroscopy. A comparison between the dose results and the European Diagnostic Reference Levels (EDRL) is made.     

The calibration of dosimetry instruments used in interventional radiology

No general agreement about the definition of the patient dose exists. As regards the radiation health risk, the doses to specific organs, Hi, are the ultimate measures for a patient dose. Values of the calibration measured, Hi, are provided only by calculational means. Out of the whole process of patient dose determination, the instruments to measure X ray spectra, FSD, field dimensions and Ka can be calibrated, X ray quality is derived from the total filtration and kV value. The actual dynamic and X ray quality ranges shall be considered when air kerma and DAP meters are calibrated. A DAP meter measurement averages the uniform radiation field specific for the X ray tube assembly used and for the beam shaping technique performed. Therefore, a DAP meter calibrated on site is preferable for patient dosimetry in interventional radiology.     

Radiation protection issues for laser-based accelerators

Radiation particles, besides their application to fundamental research, are widely applied in all fields of science (medicine, material science, chemistry, etc.). Up to today the radiations were produced by radiation sources such as accelerators, X-ray tubes, radioactive sources with the well-known problems of costs, parameters and safety. For the last few years, following the development of lasers able to focus ultra-short high-intensity pulses onto targets, the generation of ionising radiation by intense lasers has become possible. The paper will focus on some radiological protection aspects around the Frascati Laser for Acceleration and Multidisciplinary Experiments, 300 TW laser being commissioned at National Laboratories of Frascati.     

Occupational radiation protection dosimetry in Nigeria

The general features of occupational radiation protection dosimetry in Nigeria within the period 1990-1999 have been summarised. About 640 personnel, representing about 25% of the estimated number of radiation workers in Nigeria, were monitored by the TL dosimetry technique during the period, with the majority being the personnel of the teaching hospitals across the country. Most private establishments, especially the X ray diagnostic centres, operate without dosimetry coverage or supervision by a regulatory authority. The weighted mean of the annual effective dose ranged between 0 and 28.97 mSv with the upper limit of collective effective dose being 18.47 man.Sv per year. The individual risk estimate due to this is about 1.5 x 10(-3) per year and this was among the medical personnel. The value could be more if all radiation workers in the country were monitored.     

A training syllabus for radiation protection in dental radiology

The EU Council Directive 97/43/EURATOM (MED) states that Member States shall ensure that adequate theoretical and practical training is provided for dental practitioners working with ionising radiation; this also includes the provision of continuing education and training programmes, post-qualification. The area of dental radiology is specifically mentioned in this legally binding document. The Department of Medical Physics and Bioengineering, St James's Hospital, Dublin, is particularly interested in the area of radiation protection training and routinely provides educational courses both at national and international levels. A recent review of their dental radiation protection course was undertaken in conjunction with a number of Principal Dental Surgeons within the Health Service Executive in Ireland. The revised course was delivered to over 200 dental staff members at two separate meetings during 2006. The response from attendees was very positive. It is proposed to extend this course to other dental professionals, working both in the Irish private and public health sectors in the future.