Biomed Imaging Interv J 2007; 3(2):e26
© 2007 Biomedical Imaging and
Patient dose management in digital radiography
E Vano*, PhD,
JM Fernandez Soto, MSc
Medical Physics Department, San Carlos University Hospital;
and Radiology Department, Computense University, 28040 Madrid, Spain
Purpose: To present the experience in patient dose
management and the development of an online audit tool for digital radiography.
Materials and methods: Several tools have been
developed to extract the information contained in the DICOM header of digital
images, collect radiographic parameters, calculate patient entrance doses and
other related parameters, and audit image quality.
Results: The tool has been used for mammography, and
includes images from over 25,000 patients, over 75,000 chest images, 100,000
computed radiography procedures and more than 1,000 interventional radiology
procedures. Examples of calculation of skin dose distribution in interventional
cardiology based upon information of DICOM header and the results of dosimetric
parameters for cardiology procedures in 2006 are presented.
Conclusion: Digital radiology has great advantages
for imaging and patient dose management. Dose reports, QCONLINE systems and the
MPPS DICOM service are good tools to optimise procedures and to manage patient
dosimetry data. The implementation of the ongoing IEC-DICOM standard for
patient dose structured reports will improve dose management in digital
radiology. © 2007 Biomedical Imaging and Intervention Journal. All rights
Keywords: Digital radiography, patient dose, DICOM header audit, quality assurance
While digital techniques in radiology have the potential to
reduce patient doses, they also have the potential to significantly increase
them. This is a technology that is advancing rapidly and will soon affect
hundreds of millions of patients. If careful attention is not paid to the
radiation protection issues of digital radiology, medical exposure of patients
will increase significantly without concurrent benefit .
Patient dosimetry and evaluation of image quality are basic
aspects of any quality control (QC) program in diagnostic radiology. Image
quality must be adequate for diagnosis and obtained with reasonable patient
doses. No dose limit applies to medical exposure to patients but diagnostic
reference levels (DRLs) or reference values (RVs) have been proposed by the
International Commission on Radiological Protection (ICRP) [2, 3], and specific
legislation and guidelines requiring Member States to adopt such DRLs have been
published in the European Union (EU) [4, 5].
The implementation of digital radiography techniques can
entail an increase in patient radiation doses  if a strict QC program is not
launched in parallel. One of the main causes for the increase is the wide
dynamic range of the digital imaging systems, which allows overexposure with no
adverse effect on image quality. In addition, the lack of specific training in
the new digital techniques for some radiographers and the lack of well
established methods to audit patient doses in digital systems can worsen the
problem of patient exposure.
The ICRP became aware of this risk and launched several
specific recommendations to manage patient doses in digital radiology .
These recommendations include appropriate training, particularly in aspects of
patient dose management, revision of DRLs and frequent patient dose audits. In
addition, the ICRP recommended that the industry promote tools that inform
radiologists, radiographers and medical physicists about exposure parameters
and the resultant patient doses.
Some EU countries require patient dose evaluation of a
sample of patients of standard size for a standard procedure in all X-ray rooms
on a yearly basis, as well as comparison of the results with the DRLs. If DRLs
are consistently exceeded, appropriate corrective action and investigation of
the causes are required to reduce doses while maintaining suitable image
quality . The large dynamic range of digital radiology modalities could
result in patient overexposure for long periods if patient dosimetric audits
are only performed on an annual basis, as typically, for conventional
screen-film radiography. With conventional screen-film radiography, systematic
overexposure is readily apparent because of elevated film blackening. This is
not the case with digital techniques, and implementation of continuous patient
dose monitoring instead of isolated annual evaluations will help to improve
patient protection by avoiding systematic overexposures for long periods.
The purpose of this paper is to describe the different
methods of patient dosimetry reporting and the experience with some
software-assisted audit systems to survey patient doses online.
Practical experience and some of the presented results have
been obtained in a university hospital with 965 beds and 336,840 radiological
examinations in 2004. All the digital modalities of the Radiology Department
send their images to a PACS, connected with a workstation of the Medical
Physics Service, to extract the information contained in the DICOM header and
to audit image quality with a dedicated software called “QCONLINE”. Four interventional
cardiology laboratories (working with an independent PACS) have also been
connected to this workstation. The transition from conventional to digital
radiology started in 1999 in that hospital.
The first “online patient dose monitoring system” was
described for CR auditing in a previous publication . Three X-ray generators
(Philips Optimus 50) were linked directly to a personal computer through the
patient data organizer (PDO) system, also from Philips. The technical
parameters for exposure were sent to a workstation in the Medical Physics
Department, where they were kept in a database and an automatic evaluation was
done based on the calculation of the varying average values of patient entrance
dose (PED) and dose-area product (DAP) from the 10 most recent patients, for
each examination type. Comparison of averages with DRLs gave rise to warning
messages when DRLs were exceeded, prompting corrective action.
Since this initial experience, the auditing system was
empowered by processing further information from the DICOM header, which
currently is not restricted to only doses. Now, data on relevant exposure
parameters and details on the imaging procedure are also provided. As a link
with images, demographic and technical data have been implemented, allowing
image quality also to be audited and to accomplish the whole QC process on an
individual basis, if required, keeping dosimetric and procedural parameters
related with the clinical images. The analysis of DICOM headers also permits
the evaluation of modalities other than CR, such as flat detectors (DR),
interventional radiology and cardiology (XA), and computed tomography (CT), depending
on the contents of the corresponding header.
The three DR rooms of the Radiology Department are connected
to the online audit system (General Electric Senograph 2000d for mammography,
General Electric Revolution Xqi for chest and Philips Digital Diagnost for
trauma examinations). The department also has eight conventional rooms and four
mobile X-ray units digitised with five CRs (AGFA CR Compact and CR 75), three
helical CT (General Electric HiSpeed), one multislice CT (Philips Brilliance -
64 slices) and two interventional radiology rooms (a Philips Allura FD20
flat-panel unit and a Toshiba DFP2000 unit). All these modalities are connected
to an AGFA Impax 5 PACS through a fast Ethernet network. The Interventional
Cardiology Department includes three Philips Integris rooms (3000 and 5000) and
a Philips Allura FD that are connected to a Philips Inturis PACS. Both
departments are under a quality assurance program developed by the Medical
Physics Department of the hospital.
Images from each examination are sent to the corresponding
PACS and then automatically routed to a workstation at the Medical Physics
Department. Then the in-house software based on Microsoft Visual Basic 6.0
receives and presents the images, extracts the DICOM header and adds it to a database.
At the workstation, a survey of relevant parameters (depending on the
information contained in the DICOM header of each modality) is performed by
comparing their current values for a given imaging procedure with values
considered suitable (DRLs in the case of dosimetric data). A warning message is
presented on the screen for parameters out of range, thus corrective action can
be undertaken if required. By default, images received from flat panels, CR
systems and interventional laboratories (only one frame per series in this
case, initially) are presented on the QC workstation screen for basic image
quality inspection, so that it is possible to monitor it in real time. By
software, images giving rise to a warning are stored in the workstation hard disk
with the alarm source recorded as another attribute in a private field at its
The DICOM header of each modality has been analysed to
identify the fields that are useful for auditing purposes:
CR images contains information about examination, plate identification
and number of uses, exposure level (parameter defined by the manufacturer), and
processing parameters. Audited parameters are the number of exposures in the
plate and exposure level. No information is provided about technique that can
be used to calculate patient doses, so for this modality the first prototype of
the online audit system is still in use, in additional to DICOM header
analysis. It is based on a direct connection between the X-ray generator and a
computed, rather than registered, technical parameters (kVp, mAs, focus,
distance focus-film and collimators position) after each exposure. These data
are sent to a workstation in the Medical Physics Department where the software calculates
the entrance surface dose by using the X-ray tube output, which is measured
periodically as part of the QC program. (PED is the absorbed dose in air at the
surface of the patient in the centre of the irradiated area, including the
backscattered radiation from the patient). For each examination type, a
standard patient thickness is assumed for entrance dose estimation. The
computer application also allows online comparison of the mean patient dose
value for a recent sample with the local diagnostic reference levels in order
to audit dose levels and introduce corrective action if necessary.
Mammography DR images contain all the technique parameters (kVp, mAs,
focus size, distance focus-detector, anode and filter selection, manual or
automatic exposure mode, compression force, compressor position, patient
thickness, detector temperature, etc.), and a calculation of PED and glandular
dose. Most of these parameters are audited and the dose calculations are
verified periodically by using the results of the QC programme.
Chest and trauma DR images also contain all the technique parameters and
a calculation of PED and DAP that are audited and periodically verified.
Interventional radiology and cardiology modalities were acquired with a
DAP meter, which depending on the manufacturer, include this value in the DICOM
header. Other useful information for audit purposes are number of frames per
series, runs per procedure, kVp, mA, pulse time, distances and C-arm
Recent CT units include in its header information, CTDIvol, kVp and mA
that can be used in auditory.
The last development in the system (still a work in
progress) is a new module to collect and process the relevant information
transferred by the MPPS DICOM service, that could be specially useful for XA
and CT modalities because it provides information regarding the whole study
such as total fluoroscopy time or total PDA (and cumulative air kerma for some
of the new systems) in XA procedures, and dose length product (DLP) in CT.
Most of the interventional radiology systems have at
present, the capability to produce “patient dose reports” containing relevant
information to help in the audit process and to detect abnormal dose values,
which are very useful in the optimisation process. Total DAP for fluoroscopy
and image acquisition, total fluoroscopy time, and radiographic techniques for
the different series (including sometimes the DAP per series) are reported.
The International Electrotechnical Commission (IEC) is
working on a standard (recognised as “DICOM-DOSE”) written in concert with
DICOM WG-02. In the standard, it is proposed that an “irradiation object” be
stored for each irradiation event, irrespective of the storage of the images
produced by that irradiation. The irradiation objects, along with other
information, shall be stored in a “Radiation Dose Structured Report” (RDSR).
The RDSR could be archived in the RIS or PACS or perhaps transferred to a “Radiation
Safety Reporting System” (RSRS).
The IEC “new work item proposal”, identified as 62B/645/NP,
and proposed by Germany on 12 January 2007 was circulated for voting until 20 April 2007, with the name “Radiation dose documentation – Part 1: Equipment for
radiography and radioscopy”. The scope of the document encompasses all forms of
projection radiographic equipment incorporating the means for measuring or
calculating dose-related quantities, and capable of producing DICOM compatible
images and/or reports. The document provides specific units and quantities. It
does not apply for dental radiography and radioscopy, mammography and computed
Results are reported for projection radiography as PED is
equivalent to entrance air kerma (with backscatter). DAP values shall be
understood as equivalent to air kerma area product.
At the beginning of the CR system implementation and during
the transition from conventional screen-film to digital radiology in the centre
studied, mean PED values were 30% higher in certain rooms, as compared with
those found in conventional screen-film radiography rooms. This was mainly due
to lack of training of the radiographers with regard to the new systems,
especially in rooms without automatic exposure control, since the image quality
after post-processing was poor only in cases of underexposure.
The QCONLINE system has been in service for more than 3
years. During this time, a significant part of the procedures carried out at
the hospital has been audited as a pilot action. For mammography, images from
over 25,000 patients, over 75,000 chest images, 100,000 CR procedures and more
than 1,000 interventional radiology (IR) procedures, have been used.
Owing to the QA running programme, very few alarm signals
were generated on mean values out of range. For chest examinations, for
example, only three cases of mean values above 0.3 mGy for PA projection were
observed during the initial 18 month period. For IR, alarms were mainly related
to procedures exceeding 2,500 frames (in cardiology). Local reference values
(RVs) (calculated as the 3rd quartile of the dose distributions)
resulted between 30% and 60% lower than the entrance surface dose (ESD) of European
reported RVs, while showing good image quality (as reported by the radiologists
in charge of these evaluations).
Some EU countries’ regulation on quality assurance
programmes requires patient dose evaluation of a sample of patients of standard
size for a standard procedure in all X-ray rooms on a yearly basis, and this
system gives the possibility to evaluate patient doses in all of them instead
of in a sample, thus any deviation can be immediately corrected.
Another important exploitation of the DICOM header
information contained in the cine series of the cardiology procedures is the
orientation of the X ray beam. Figure 1 presents a graph of this orientation
for a sample of 4,020 series. This information allows estimation of the level
of scatter dose in the cardiology laboratories (very dependent on the C-arm
The information on the angulations of the C-arm, together
with the radiographic technique of the different series (or the DAP or cumulative
dose per series) and the geometrical data (distances and radiation field size)
allows calculation of the skin dose distribution. Figure 2 presents one example
of this calculation, which is compared with the experimental skin dose
distribution measured with a slow film position between the table and the
The transfer of the patient dose reports to a database
allows the collection of large samples for statistical calculations of patient
doses and to have access to individual dose data in the case of repeated
procedures or high individual dose data. Table 1 and Figures 3 and 4 show the
results for the cardiology procedures during 2006 at the centre.
Discussion and Conclusion
Systems of QCONLINE have demonstrated their benefits to
manage patient doses in digital radiology. The pilot system described operated
long enough to establish its reliability and has demonstrated the possibility
offered by the contents of the image DICOM header to monitor dose levels in
real time, to compare them with DRLs and later to analyse the causes producing
abnormal values, based on inspection of other chosen parameters such as
exposure mode and technical parameter set. The possibility of implementing this
QC system with a direct link to the modalities, without the need of a PACS, is
another interesting feature. The aim is to implement it in small centres, on
whatever system including the DICOM storage services, and through the intranet
real-time dose monitoring system that has been described as an appropriate
quality control tool to ensure that radiation doses remain within selected
norms. Because of the ease with which doses at CR can be increased, eluding
identification of the problem for an extended period, this type of tool allows
replacement of advantageous annual dosimetric evaluations in patients.
Supported in part by the European Commission (SENTINEL
coordination action FP6-012909), the Spanish Ministry for Science and
Technology (project FIS2006-08186), and the Spanish Nuclear Safety Council.
Figure 1 Common projections in a cardiology room obtained from the DICOM header.
Figure 2 Use of DICOM header information to calculate skin dose distribution.
Figure 3 Patient dose distribution for coronary angiography.
Figure 4 Patient dose distribution for coronary therapeutic procedures.
Table 1 Statistical results of the cardiology procedures during 2006.
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|Received 18 March 2007; accepted 25 March 2007
Correspondence: Medical Physics Department, San Carlos University Hospital, 28040 Madrid, Spain. Tel./Fax: + 34 91 330 3302; E-mail: firstname.lastname@example.org (E. Vano).
Please cite as: Vano E, Fernandez Soto JM,
Patient dose management in digital radiography, Biomed Imaging Interv J 2007; 3(2):e26
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