Patient exposure monitoring in medical imaging: Why and how?

Vassileva, ICDA-3 2019, Lisbon
Patient exposure monitoring in
medical imaging: why and how?
Jenia Vassileva, Ph.D.
Radiation Protection Specialist
Radiation Protection of Patients Unit
International Atomic Energy Agency, Vienna, Austria

Objectives
To learn about the main features of a system for recording,
collecting, and analizing dosimetric data
To become familiar with different analytical uses of collected
dose data
To understand how patient exposure monitoring fits into the
framework of continuous optimization of medical imaging




Goal and Strategy
GOAL
What and why we
would like to achieve
STRATEGY
How we will achieve
the goal
PLAN
What actions we will take to
fulfil the strategy and succeed

Effective
diagnosis
Effective
treatment
Positive effect
on patient
health and life
The goal of medical practice

Effective
diagnosis:
•right diagnosis
•timely diagnosis
•minimum risks
The goal of diagnostic imaging practice
✓ Imaging modality
✓ Equipment: availability, performance, operation
✓ Human factor: knowledge, skills, attitude
✓ Patient history and clinical information
✓ Economic factors

Effective
diagnosis:
•right diagnosis
•timely diagnosis
•minimum risks
The goal of diagnostic imaging practice
Radiation protection perspective:
Optimization of protection: Keeping the
exposure of patients to the minimum
necessary to achieve the required
diagnostic or interventional objective.

Diagnostic accuracyVisualization capability
Medical imaging objective: effective diagnosis
Image
production
Image
interpretation

Medical imaging objective: effective diagnosis
Diagnostic accuracy
depends on:
✓ knowledge and experience;
✓ availability of patient history;
✓ availability of other clinical
information;
✓ diagnostic criteria;
✓ viewing conditions
Visualization capability
=Image quality
=Useful diagnostic content
depends on:
✓ imaging modality;
✓ equipment:
✓ availability;
✓ performance;
✓ operation

Radiation risk
Risk of ionizing radiation
depends on:
✓imaging modality;
✓equipment:
✓ design;
✓ performance;
✓ operation;
✓human factor:
✓ education and training
✓ safety culture

Patient
dose
Image
Contrast
SNR
Image quality and patient dose
Photon energy, keV
Attenuationcoefficient
bone
muscle
fat

• Optimisation of protection is not minimisation of dose
• Too low a radiation dose could be as bad as too high a radiation
dose, in that the consequence could be that the images obtained
are not of suitable diagnostic quality.
• It is of paramount importance that the medical exposure leads to the
required outcome.
Optimization of protection (International BSS)

Registrants and licensees and radiological medical practitioners
shall ensure that protection and safety is optimized for each
medical exposure
Components to consider:
1.Design considerations for equipment
2.Operational considerations
3.Dosimetry of patients
4.Diagnostic Reference Levels (DRLs)
5.Calibration
6.Quality assurance
7.Dose constraints (for carers and comforters)
Monitoring patient dose
is a key requirement
toward optimization

Registrants and licensees shall ensure that:
• Dosimetry of patients is performed and documented …, to
determine typical doses to patients for common diagnostic and
for image guided interventional procedures;
• Local assessments… are made at approved intervals for those
radiological procedures for which DRLs have been established;
• A review is conducted to determine whether the optimization of
protection for patients is adequate if typical doses exceed the
relevant DRL, or they fall substantially below the relevant DRL and
the exposures do not provide useful diagnostic information …
• Records are maintained of dosimetry of patients and local
assessments and reviews made with regard to DRLs
13

Terminology
15
•Patient exposure
data
•Exposure
monitoring
•Recording patient
exposure data
•Collecting patient
exposure data
•Tracking patient
exposure data
•Managing patient
exposure data
A process including the mechanism and the operational elements related to
collecting, interpreting, and acting upon quantities associated with clinical
imaging operation
A process of documenting patient exposure data manually or electronically
A process of gathering patient exposure data into a common system. The
term can be used synonymously as recording and collecting together
An analysis process of ascertaining and monitoring temporal trends in
individual or collective stored data
A process of oversight through exposure data recording, tracking, and
analysis towards improvement of radiation protection and patient care
A collection of metrics characterizing patient exposure to ionizing radiation
including both modality-centric and patient-centric quantities

Patient dose metrics
16
Application Dose quantity Dose unit
•Plain radiography,
including dental
•Mammography
•Fluoroscopy &
fluoroscopy guided
interventional
procedures
•Computed tomography
•Nuclear medicine
Entrance surface air kerma, Ke
Kerma-area product, PKA
mGy
μGy.m2
Incident air kerma, Ki
Mean glandular dose, MGD
mGy
mGy
Kerma-area product, PKA
Cumulative air kerma at the
interventional reference point
Gy.cm2
mGy
CT air kerma index, C
Air kerma-length product, LKP
mGy
mGy.cm
Administered activity MBq

Entrance surface air kerma, Ke
Unit: Gy
Direct measurement with TLD
Calculation from the tube output
Ke = Ki. B
В – Backscatter factor (1,2 – 1,4)
Dose quantities: Radiography

Kerma-area product (KAP)
Unit: Gy·m2 (µGy.m2 = cGy.cm2)
Transparent ionization chamber
Dose quantities: Radiography and fluoroscopy
18

Cumulative air kerma at the
interventional reference
point
Dose quantities: Fluoroscopy
Unit: mGy

Dose quantities: Computed tomography
20
Computed-tomography air
kerma index, C
Unit: mGy
Air kerma-length product, LKP
Unit: mGy.cm

Computed-tomography air
kerma index, C
10 cm ionization chamber
Measurement in air or
in a phantom: 16 cm for head
and 32 cm for body
Dose quantities: Computed tomography

RECORDING COLLECTING ANALYZING
Storing
(archive)
Sub-
archives Storing
Patient exposure data workflow
22

• Facility (modality) level
• Multi-facility
• Hospital
• A region in the country
• Country
• Region of more countries
• International
Patient exposure monitoring strategy
23
Hospital A Hospital B Hospital C
Hospital E
Hospital FHospital Z

24
Monitoring at population level
(group)
Tracking at individual level
Hospital A Hospital B Hospital C
Hospital E
Hospital FHospital Z

Exposure monitoring at population level
25
• For group of patients
• No need of patient ID
• Measurable dose quantities (modality specific)
Monitoring at population level
(group)
Used for:
– Optimization
– Benchmarking
– Trends over time
– Quality assurance

• Consistent with the general tendency of patient-centered (personalised) health care
• Unique patient identifier is critical
• Dose metrics related to individual radiation risk (?): ideally to account for patient size,
age; gender; morphology; biokinetics (NM) …
Exposure tracking at individual level
26
Tracking at individual level
Quantities related to individual
risk: organ doses, effective
dose (?) or other risk index?
•Who will have access?
•Education of users

Individual tracking for
justification and
optimization
Referral guidelines,
CDS, Justification;
Epidemiology, Research
At population level (group of patients) For individual patients
Patient data, procedure data and
modality specific dose indices (KAP, CTDIvol, DLP,
CD, PSD, ..), plus IQ indices
Frequencies
(number) of
procedures
Patient
identification
(ID)
DRL; Typical dose
levels; Alert levels
Optimization of
patient protection
and imaging practice
Organ doses
Effective dose
(or other risk index)
Population doses
(trends,
comparison)
Organ doses
Effective dose
(or other risk index)

RECORDING
1. Manual recording (at modality):
- Paper
- Into RIS
2. Electronic recording of radiation exposure
details in a standard format (at modality):
• Non-DICOM dose objects
- Modality Performed Procedure Step (MPPS) to HIS/RIS
- Image “header” attributes
- Bitmap (graphic) images in PACS and Optical character
recognition (OCR) conversion
• DICOM object:
- For each radiation event
- Collected in a unique object (DICOM Radiation Dose Structured
Report): Includes patient demographics, study information,
imaging technique, geometry and dose metrics
Storing
(archive)
Patient exposure monitoring workflow
28

Data to be recorded
• Level 1 (Minimum requirements):
The first order data are relevant to characterize the exposure and contain information that
can be easily derived from the patient and exam records in the RIS and dosimetric
quantities that the equipment can provide (calculated or measured).
• Level 2 (Standard requirements):
The second order data contain more capillary information. In particular data for the single
irradiation events are included for every modality. Scope of this set of data is to refine the
exposure conditions in order to estimate single patient dose. The level of accuracy in the
calculations depends on the amount of information collected.
• Level 3 (Advanced requirements):
The third order of data is used for the optimization and includes derived dosimetric data
(e.g.: organ doses including peak skin dose for IR), information linked.
29

Data to be recorded (example: Radiography)
30
• Level 1:
- Number and type (e.g. AP/PA/Lat) of radiographic projections
- Per projection:
- KAP value
- If KAP meter is not available:
kV, mAs, Source-detector distance, Tube output, ESAK (calculated or measured)
• Level 2:
- kV; mAs; Source-detector distance; Source-patient distance; Entrance surface air kerma; Exposure time;
Filtration; Field size; Grid; Film-screen combination speed, or Exposure index and Deviation Index (for CR/DR)
• Level 3:
- Focal spot size; Post-processing settings
- AEC (Y/N; chamber location)
- Matrix size; Pixel size; Bit stored
- Organ dose
- Image quality
KAP
ESAK

31
•Collection of data from
different dose objects
• Different patients/ X-ray unit/
modality/ facility/ region/ country……
• Using standardized templates
(reflecting the purpose of the
collection
•Means
• Electronic
• Manual (paper)
•Stored for further processing
RECORDING COLLECTING
Storing
(archive)
Sub-
archives

Exposure data collection
• Definition of the group (classification)
▪ Examination parameters
▪ Patient parameters
▪ Acquisition parameters
32

• the modality (i.e., CT, radiography, etc.),
• the procedure (e.g., abdominal CT, chest
radiography)
• sub-procedure (e.g., PA or lateral view),
• the clinical indication targeted for the examination
(e.g., liver lesions)
• the complexity of procedure
33

• Definition of the group
(classification)
• the patient type (e.g., adult, pediatric,
inpatient, outpatient, emergency patients,
etc.)
• patient characteristics (e.g., gender, age,
weight, body mass index, diameter
34

▪ Acquisition parameters
• specific imaging system used to acquire the
images (make and model, software version)
• the room used to perform the examination
• the timing of the examination (e.g. shift, period
of year, etc)
• the radiographer/ technologist who performed
• the specific imaging protocol invoked in the data
acquisition.
35

36
RECORDING COLLECTING ANALYZING
Storing
(archive)
Sub-
archives Storing
• Statistical analysis
• Trends (per protocol, per group, per facility,….)
• Temporal changes
• Population analysis (DRLs, collective dose to population,
epidemiological studies, research….)
• Individual tracking, etc

Analysis: Establishing DRLs and typical doses
• For DRL setting: Representative survey
–Wide-spread in terms of various types and size of facilities
(rural, urban, private, public), equipment, and geographical locations.
–A snap shot of current practice in the country or region is obtained, reflecting
both good and poor practices, for that particular imaging procedure.
–The DRL is typically the rounded 75th percentile of the distribution of typical
(median) doses for the room or facility
–Excludes high dose ‘tail’ of distribution
37

Analysis: Establishing DRLs and typical doses
• National/ regional dose registries
38

Analysis: Benchmarking against DRLs
39
Courtesy K. Kanal

Analysis: Identifying and investigating
over-exposure and under-exposure
40
Courtesy E. Samei, DUMC

Analysis: Inter-system variability
41
D.Frush; E. Samei, CT Radiation Dose
Monitoring: Current State and New
Prospects, Medscape Radiology, 2015
CT scanner 1
CT scanner 2

Patient exposure monitoring software
• Commercial and open source
• To provide standardized and validated data for transfer to
vendor neutral archieves
42
Interoperability among modalities:
• The IHE profile serves as an
implementation guide for vendors
• REM profile ensures interoperability
among modalities, PACS, dose report
systems and even national archives.

Patient radiation exposure monitoring
Ideally, exposure monitoring need to be integrated with the
general patient information systems (Electronic Health Records,
EHR):
• Patient related data
• Images
• Imaging reports
• Exposure related quantities
and connected to the electronic referral and clinical decision
support (CDS) systems.
43

Patient Organizations ordering
radiology services
Users of exposure monitoring systems
Equipment vendors
(for maintenance and
development)
44
Research
institutions
Radiation
protection
authority
Medical physicist in charge
of patient exposure data
management
Specific needs of different users  Specific rights for extracting and analysing
the patient exposure data  Specific platform (dashboard) for each group with
particular features, objectives and desired outputs.
Radiographers having a
specified role in data
management
Referring
physician
Health
Authority
Radiology department
and/or hospitals providing
radiology services
IT expert services of the
hospital (for maintenance
and development)
Radiological professional
responsible for procedures

Challenges: Data quality and accuracy
•Calibration and checks of the dosimetric information provided by the
equipment (integrated dosimeters and software that calculates, displays and
report dose metrics)
•Verification of the data transmitted to the archives
(PACS, RIS, Dose Tracking System, Dose Registry).
•Verification of data analysis
•QA program
‐ Clearly defined responsibilities
‐ Role of the facility’s medical physicists working with the equipment/ dose
monitoring software vendor
‐ Training of all users - initial and continuous
‐ Regular reports: at least annually
45

Challenges
• Classification (coding) problems:
Need of standardization of examination nomenclature
• Data collection parameters:
Statistical requirements, representativenes, sample sizes, etc.
• Patient group definition:
Distinction of paedaitric examinations, age, weight or size based grouping of
patients; Availability of patient weight
• Information management (IT) problems:
Data protection, access control, privacy and confidentiality regulations, use of
cloud computers, ethical considerations
46

Conclusions
• Patient dose monitoring is a key requirement toward optimization.
• It is an objective tool for impovement of radiation protection, but can serve
also the wider goal of optimizing healthcare resources.
• For most effective use, the exposure management should be integrated into
the electronic health care management systems.
• Human and technologic resources are necessary.
• The automatic exposure management system is a tool to
facilitate the efficient collection and distribution of dose
information, but it needs systematic QC for validation of
data recording, transfer, collection and analysis.
• The team work is crucial for defining the strategy and
implementation plans
47

Vassileva, ICDA-3 2019, Lisbon j.vassileva@iaea.org
Thank YOU!
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Patient exposure monitoring in medical imaging: Why and how?

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