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.     

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.     

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 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.     

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.     

Quality control of equipment used in digital and interventional radiology

Digital and interventional radiology are increasingly important areas of radiology. Quality control (QC) of such equipment is of particular importance to avoid unnecessary high doses and to help to achieve good image quality. Within the DIMOND III project, equipment requirements and specifications for digital and interventional radiology have been formulated. A protocol for QC tests has been drafted based on various national and international recommendations. Tests are included for various parts of the imaging chain, i.e. X-ray tube and generator, X-ray tube control system, laser printer and display station, and image quality and patient dose. Preliminary tolerance levels have been set for the various tests, after initial measurements. To check the suitability of QC tests and stated tolerance levels, measurements were made at the University Hospital Gasthuisberg in Leuven for equipment used for paediatric radiology and a unit used for chest examinations. The results of the various tests are reported.     

Equipment requirements and specification for digital and interventional radiology

During the past decade there has been a substantial growth in digital and interventional radiology. Equipment requirements and specification for digital (interventional) radiology are necessary to facilitate the purchase of proper installations for specific purposes. Inappropriate equipment might lead to increased dose to patients and staff, insufficient image quality and, for interventional radiology, to inefficient procedures and the potential for deterministic effects to occur. The equipment requirements and specifications are of various types. Requirements for dose displays and dose record keeping are dealt with in a separate contribution to this workshop. Detailed information is presented in this contribution on requirements and specifications in relation to ergonomic, dosimetric and image quality aspects.     

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.     

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.     

ICRP special radiation protection issues in interventional radiology, digital and cardiac imaging

The International Commission on Radiological Protection (ICRP) has published two reports giving recommendations dealing with the avoidance of deterministic injuries in interventional radiology and the management of patient dose in digital radiology in 2001 and 2004, respectively. Another document, on radiation protection for cardiologists performing fluoroscopically guided procedures, will be produced during 2005. This paper highlights some of the topics of the published reports, their relevance to European legislation on medical exposures and the importance of radiation protection research in underpinning the ICRP task groups' work in to producing these documents. It is also anticipated that the results, obtained in the cardiology work package of the European research project, will be used in the new document on radiation protection for cardiologists.     

Doses to operators during interventional radiology procedures: focus on eye lens and extremity dosimetry

The present study is focused on the personnel doses during several types of interventional radiology procedures. Apart from the use of the official whole body dosemeters (thermoluminescence dosemeter type), measurements were performed to the extremities and the eyes using thermoluminescent loose pellets. The mean doses per kerma area product were calculated for the monitored anatomic regions and for the most frequent types of procedures. Higher dose values were measured during therapeutic procedures, especially embolisations. The maximum recorded doses during a single procedure were 1.8 mSv to the finger (nephrostomy), 2.1 mSv to the wrist (liver chemoembolisation), 0.6 mSv to the leg (brain embolisation) and 2.4 mSv to the eye (brain embolisation). The annual doses estimated for the operator with the highest workload according to the measurements and the system's log book were 90.4 mSv to the finger, 107.9 mSv to the wrist, 21.6 mSv to the leg and 49.3 mSv to the eye. Finally, the effect of the beam angulation (i.e. projection) and shielding equipment on the personnel doses was evaluated. The measurements were performed within the framework of the ORAMED (Optimization of RAdiation Protection for MEDical staff) project.     

Patient dosimetry and image quality in digital radiology from online audit of the X-ray system

The present work describes an online patient dosimetry and an image quality system in digital radiology. For the patient dosimetry audit, current mean values of entrance surface dose (ESD) were compared with local and national reference values (RVs) for the specific examination type evaluated. Mean values exceeding the RV trigger an alarm signal and then an evaluation of the technical parameters, operational practice and image quality was begun, using data available in the DICOM header to derive any abnormal settings or performance to obtain the image. The X-ray tube output for different kVp values is measured periodically, to allow for the automatic calculation of ESD. The system allows also for image audit, linking the dose imparted, the image quality and the alarm condition, if produced. Results and the benefits derived from this online quality control are discussed here.     

Monte Carlo calculations on extremity and eye lens dosimetry for medical staff at interventional radiology procedures

There are many factors that can influence the extremity and eye lens doses of the medical staff during interventional radiology and cardiology procedures. Numerical simulations can play an important role in evaluating extremity and eye lens doses in correlation with many different parameters. In the present study, the first results of the ORAMED (Optimisation of Radiation protection of MEDical staff) simulation campaign are presented. The parameters investigated for their influence on eye lens, hand, wrist and leg doses are: tube voltage, filtration, beam projection, field size and irradiated part of the patient's body. The tube voltage ranged from 60 to 110 kV(p), filtration from 3 to 6 mm Al and from 0 to 0.9 mm Cu. For all projections, the results showed that doses received by the operator decreased with increasing tube voltage and filtration. The magnitude of the influence of the tube voltage and the filtration on the doses depends on the beam projection and the irradiated part of the patient's body. Finally, the influence of the field size is significant in decreasing the doses.     

Staff dosimetry in interventional cardiology

In interventional cardiology (IC) staff can be exposed to high dose levels due to the long fluoroscopy procedures performed. Staff dosimetry can yield information on the optimisation level of radiation protection, which is influenced by the equipment performance, auxiliary protection devices, training in radiation protection and procedure complexity. Staff exposure data assessed in haemodynamic laboratories of four hospitals in Spain, Greece and Italy participating in the DIMOND concerted action are analysed and compared with data in the literature.     

The value of digital personal dosemeters in angiography/interventional radiology: preliminary experience

New interventional procedures tend to involve longer screening times than were hitherto used in radiology. A careful audit of technique and shielding facilities needs to be performed to ensure that patient and operator doses are optimised. This paper explores the use of digital dosemeters to evaluate operator dose. Equipment related parameters, e.g. screening time, dose-area-product (DAP) readings, were not found to be strongly correlated to operator dose. The real time display on the electronic dosemeter is a non-intrusive indicator of the efficacy of operator protection strategies.     

Deterministic effects in interventional radiology

Since the development of interventional radiology, the number and complexity of procedures has increased significantly and continues to grow. Interventional radiology procedures offer substantial health care benefits. However, associated with the increasing complexity as well as a lack of quality control programmes and specific training in radiation protection, there is an increase in the occurrence of deterministic effects in both patients and staff. There is a growing literature of case reports describing deterministic effects. A review of some case reports and the response of various international organisations is presented. It is important that workers in interventional radiology are aware of the potential for deterministic effects and the dose threshold for their onset, so that patients can be followed up appropriately.     

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.     

Quantification of risk-benefit in interventional radiology

The increased use of interventional radiological procedures brings with it an increased risk of cancer induction due to the possible high radiation levels used. This risk must be balanced against any viable alternatives and should take into account the individual risks and benefits. The purpose of this study is to quantify this risk benefit in terms of quality-adjusted life years (QALYs) of a procedure and its alternatives, including the risk due to the radiation. Uterine fibroid embolisation was chosen as a model study with data collected both on the outcomes of procedures in terms of complications and quality of life in the long-term and on radiation dose delivered to the patient. Dosimetry data were obtained from University Hospital Galway. The risk was then calculated using the BEIR VII model of dose-response for low linear energy transfer (LET) radiation. In this case, it was found that the radiological technique has distinct advantages over hysterectomy and myomectomy in terms of QALYs. The increased risk due to radiation from the procedure is small when compared with the overall benefit to the patient. Probability of stochastic effects based on the average dose per procedure carries an attributable risk (fatal and non-fatal cancer and hereditary effects) of 0.4% or a relative risk of 1.09%. The method described here can readily be adapted to other interventional procedures.     

Quality control and patient dosimetry in digital radiology. On line system: new features and transportability

New features have been added to a system (QCONLINE) for auditing patient dosimetric and technical parameters 'on line', working on a digital radiology department and using the information contained in the DICOM header of some modalities. The audit of other parameters than patient doses have been included, setting alarm conditions to alert on malfunction of the X-ray system or bad operation modes, in addition to the evaluation of patient doses. A new module to analyse, collect and process the relevant information transferred by the modality performed procedure step (MPPS) service has been launched. Several examples with the exploitation of the new features are presented. The transportability of the system has been tested in two remote hospitals during several months. The new MPPS module has demonstrated to be a good tool to complement the information existing in the DICOM header. The system allows to help in the optimisation of digital radiology departments managing patient dosimetry and procedure data in real time.     

Overview of double dosimetry procedures for the determination of the effective dose to the interventional radiology staff

In interventional radiology, for an accurate determination of effective dose to the staff, measurements with two dosemeters have been recommended, one located above and one under the protective apron. Such 'double dosimetry' practices and the algorithms used for the determination of effective dose were reviewed in this study by circulating a questionnaire and by an extensive literature search. The results indicated that regulations for double dosimetry almost do not exist and there is no firm consensus on the most suitable calculation algorithms. The calculation of effective dose is mainly based on the single dosemeter measurements, in which either personal dose equivalent, directly, (dosemeter below the apron) or a fraction of personal dose equivalent (dosemeter above the apron) is taken as an assessment of effective dose. The most recent studies suggest that there might not be just one double dosimetry algorithm that would be optimum for all interventional radiology procedures. Further investigations in several critical configurations of interventional radiology procedures are needed to assess the suitability of the proposed algorithms.