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How to determine examination
frequencies and population dose
estimates for XX-rays and NM?
Jenia Vassileva
National Centre of Radiobiology and
Radiation Protection
Sofia, Bulgaria
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Population dose estimates
Examinations 1, 2, 3, i
Country A, B, C, D, ……
Annual numbers of:
• all examinations
(N1, N2, N3,…..)
• per 1000 population
Ni ∗ Ei
∑
Mean effective dose
per examination
E1, E2, E3, ….
i
Annual collective dose
- total
- per 1000 population
countries - per caputa
∑
Collective dose of the
European population
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Number of categories of
examinations
225 specific types
of examination or
procedure covering
4 radiological
modalities and
based on regions
70 broad
categories of
examinations
based on
regions
20 examinations
with highest
contribution to the
population dose
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Top 20 approach (X-ray)
Frequency
50-70 %
Top 20
Collective dose
70-90%
Top 20
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
28 NM examinations
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Information on the annual numbers of examinations
conducted in a country can be obtained:
• Method A: “Sample survey”
from a sample of hospitals, clinics or practices and
then scaled up to cover the whole country.
• Method B: “Central statistics survey”
from central statistics held by government
departments or insurance companies for all
(or at least a large proportion) of radiology practice
in the country.
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
1. Representativeness
– Steps to ensure that the sample is as representative
of national radiology practice as possible.
– All types of hospital and radiological practice should
be included in the sample in similar proportions to
those occurring nationally.
Which health care providers might offer medical
radiology services?
Which are the most important contributors to
national radiology practice?
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
1. Representativeness
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
1. Representativeness
Are dental radiology conducted by dentists in ‘Dental
Practices’ is included in the population dose
assessments or not?
– little impact on the collective dose
– but a big impact on the frequency examinations
(account for at least 1/3 of all x-ray examinations in
most countries)
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Example
• Bulgaria
–
–
–
–
• Finland:
7,6 million inhabitants
480 intraoral dental systems
96 OPG
62.3/1000 exams
–
–
–
–
5,3 million inhabitants
4565 intraoral dental systems
673 OPG
469.4/1000 exams
1600
1409
1400
11891190
1200
10571087
1000
802
800
867
941
660
523
600
342
400
200
9
30
63
84
140
398
219 230
0
UA HU RO BG PT CR SK UK
LI
FR CZ NO BE DE
FI
DK LU AT CH
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
1. Representativeness
– little impact on the completeness of the frequency
data because of the insignificant contribution:
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Example: Ukraine
• Chest radiography – 6 517 527 (142/1000) exams
– Effective dose 0.1 mSv
– 652 manSv
• Fluorography –
22 894 203 (499/1000)
– Effective dose 3.3 mSv film; 0.42 mSv digital
– 61 045 manSv
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
2. Standardized categorization of exams
and sources of information:
– RIS: National coding system
– RIS: Different coding system in different hospitals
– PACS/RIS (electronic) or paper registers
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
2. Standardized categorization of exams
and sources of information.
The accuracy of the frequency data depends on how
reliably the coded information stored in the RIS can
be translated into actual numbers of examinations.
Coding system may vary with time
Cooperation between those responsible for assessing
the population dose and the designers of examination
code systems
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
3. Scaling up to the whole country:
based on different approaches, depending on what
data are available:
– the relative numbers of radiology service providers;
– the relative numbers of patients;
– the total numbers of x-ray examinations
in the sample
the whole country
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
3. Scaling up to the whole country:
Sample
Scaled by
UK
38 trusts in 2 different regions
(16% of English exams)
Total no. of x-ray
exams per trust
Switzerland
11 big hosp; 2 week survey in 274
medium & small hosp & 2787
practices
No. of hospitals &
practices with x-ray unit
Sweden
From licence holders
covering 25% of population.
Multiply by 4
Denmark
Directly from national hosps.
Chiro–39 clinics (95% survey)
Multiply by 1.05
Netherlands 90% of hospitals
No. of hospital admissions
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
Example from this survey: Switzerland
• National survey to collect the 2008 data: developed an online
database (www.raddose.ch).
• All healthcare providers invited to participate by sending their
annual frequency data for more than 225 examinations.
• Data from about 3,500 users were collected (42% response rate;
45% in terms of X-ray units)
• Extrapolated to cover the whole country according to the number
of X-ray units, taking also into account the type of healthcare
provider.
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
Example from this survey: Italy
• The survey included 5 Italian regions, accounting for
approximately 30% of the population.
• The included radiology procedures in 2006 (reference year)
• For each procedure were requested to each region both the
frequency and the dose.
• When a region was not able to provide data for a specific
examination, the results were interpolated on the basis of the
other regions data.
• Data were extrapolated to the entire Italian population
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
• 10 countries used questionnaire sent to ALL
departments using X-ray
Response rate:
–
–
–
–
–
–
Finland 98%
Greece 20%
Estonia 53%
Iceland 90%
FYR of Macedonia 97%
Montenegro 100%
– Norway 100%
– Slovenia 75% (90% of the
workload)
– Serbia 40%
– Ukraine 85%
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
• Most often used method for collection of frequency
data of NM examinations in this survey.
• Questionnaire sent to ALL NM departments
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method A: “Sample survey”
• Results collected and analyzed by the coordinating
institution (authority, institute, etc)
• Response rate of NM departments:
–
–
–
–
–
–
–
–
Bulgaria 100%
Estonia 100%
Finland 100%
Latvia 100%
FYR of Macedonia 100%
Montenegro 100%
Norway 100%
Slovenia 100%
–
–
–
–
–
–
–
–
Lithuania 100%
Ukraine 100%
Iceland 90%
Greece 70%
Serbia 71%
Portugal 73%
Belgium 66%
UK 66%
Scaling up
to the whole
country
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method B: “Central statistics survey”
Central statistics held by:
– insurance companies
– government departments
for all (or at least a large proportion) of radiology practice
in the country.
usually for a large proportion – or even the total –
of radiology practice in the country
scaling up to cover the whole country may be
still necessary
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method B: “Central statistics survey”
Sample
Scaled by
Germany
From statutory health insurance: 89%;
private health insurance: 9%; other kinds of
/ no health insurance: 2%
for about 80% of x-ray exams (out patients)
Scaling factors to estimate
inpatient data
Luxemburg
Annual nos from Nat Health Ins
(99% survey)
No scaling necessary
Belgium
Annual nos from Nat Health Ins Inst
(97-100% survey)
No scaling necessary
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method B: “Central statistics survey”
Examples from this survey
Using health insurance data:
–
–
Belgium, Germany,
Croatia (+ direct survey in 7/9 major NM dept, 5
interventional cardiology departments and one University
hospital )
Central government department statistics:
–
Bulgaria (Ministry of Health) for X-ray procedures
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method B: “Central statistics survey”
Examples from this survey
Using both:
–
–
Czech Republic - Health insurance company + Institute of
Health Information and Statistics
Slovakia - National Health Information Centre and the main
Slovak Health Insurance Companies, covering about 80% of
all X-ray and NM exams
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Method B: “Central statistics survey”
Scaling up to the whole country
Example: Romania
• Number of procedures reported to the regional Ionizing Radiation
Hygiene Laboratory, and they send data to the National Institute of
Public Health.
• In 2010: reported 29 out of 41 counties;
• Scaling up to the whole population: take into account the number of
X-ray units per type in different regions, e.g.:
"m" is the total number of reported CT examinations from
“M" CT units; "N" is the real number of CT units at country level;
"c" - the estimated number of CT examination at country level:
c=mN/M
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Mixed method A & B
France
• Survey conducted in 2007 by the Institute for radiation
protection and nuclear safety (IRSN) and the National institute
for public health surveillance (InVS).
The frequency data was obtained from two sources:
• for private practice : from the national health insurance data for
a representative sample of 1% of the population (about 500 000
persons),
• for public practice: 2 surveys in public hospitals:
– in radiology - 50 hospitals (about 12% of the public
hospitals).
– in NM, a questionnaire has been sent to the 127 public NM
departments (response rate 72%).
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Mixed method A & B
Portugal
• Frequency data from the Civil Servants' reimbursement system
(10% of exams);
• frequency data from the reimbursements of the exams
performed under the "conventioned" regime (roughly 20%);
• hospital survey by a questionnaire to obtain the annual frequency
of the exams performed in the "general regime" i.e. reimbursed
on a hospital basis); 23% representation.
• For Angiography and PTCA: information from Portuguese
Association of Cardiovascular Intervention
• summed the values
• The remainder of the exams (~5% ) not considered
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Sources of frequency data
N/A
32%
Questionnaire
22%
RIS/PACS
15%
Others
7%
Insurance
12%
Health
authorities
12%
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Using Top 20 approach to estimate
overall total collective effective dose
Frequency
50-70 %
Top 20
Collective dose
70-90%
Top 20
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Extrapolation from Top 20 to the total
• 12 countries reported total frequency of Top 20 examinations
and overall total frequency from all X-ray examinations.
• Average correction factor calculated (total overall/total TOP
20) for each main group of x-ray procedures (plain
radiography, fluoroscopy, CT and interventional radiology)
• Correction factors used to estimate overall total frequencies
from the total frequencies evaluated by TOP 20 approach
Frequency correction factors Overall total/TOP 20 total
Plain
Computed Interventional
radiography Fluoroscopy tomography radiology
2,13
2,12
1,12
2,73
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Extrapolation from Top 20 to the total
• 6 countries reported total collective effective dose of Top 20
examinations and overall total collective effective dose from
all X-ray examinations.
• Average correction factor calculated (total overall/total TOP 20)
for each main group of x-ray procedures (plain radiography,
fluoroscopy, CT and interventional radiology)
• Correction factors used to estimate overall collective effective
dose from the total evaluated by TOP 20 approach
Correction factors Overall total/TOP 20 total
Plain
radiography Fluoroscopy
CT
1,12
1,55
1,18
IR
2,61
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece
Workshop on European Population Doses from Medical Exposure
24-26 April 2012, Athens, Greece