Elaboration of New NDRLs as Part of Third
National Patient Dose Survey in Diagnostic
Radiology in Bulgaria
Asen Dimov, Ivan Tsanev, Desislava Ivanova, and Filip Simeonov
Abstract
Purpose: The aim of this research is to elaborate an update
of National Diagnostic Reference Levels (NDRLs) in
Bulgaria, as required by National and International
legislation. Methods and Materials: Special questionnaires and methodology instructions for submission of
required data were distributed to all hospitals in the
country. Patient dose records and corresponding technical
data were delivered from medical institutions via following three methods: by e-mail, by specialized on-line
system, or by paper. A national patient dose database
build on MS Access was elaborated and employed for
storing, processing and analysing of the collected data.
Results: More than 10,500 patient dose records on more
than 190 X-ray systems from over 90 health establishments have been collected and analysed. New national
DRLs were elaborated and proposed for: Chest PA,
Pelvis AP, Abdomen AP, Thoracic Spine AP, Thoracic
Spine Lat, Lumbar Spine AP, Lumbar Spine Lat,
Skull AP, Scull Lat, Barium meal, Barium enema,
Coronary Angiography and Percutaneous Coronary Intervention—in terms of KAP; for Computed Tomography
(CT) of Head, Abdomen and Lumbar Spine—in terms of
CTDIw and DLP; for Mammography—in terms of ESAK
and AGD. Conclusion: The new DRL values obtained are
proposed as NDRLs for the country. Most are comparable
with other European NDRLs with a few exceptions only.
Those exceptions are most probably related to actual
optimization in existing radiology practices.
Keywords
NDRLs
Patient dose
Diagnostic radiology
A. Dimov (&) I. Tsanev D. Ivanova F. Simeonov
National Centre of Radiobiology and Radiation Protection, 3, Sv.
Georgi Sofiyski Street, 1606 Sofia, Bulgaria
e-mail: adimov_sl@yahoo.com;
a.dimov@ncrrp.org; a.dimov07@gmail.com
1
Introduction
Establishment, regular review and use of diagnostic reference levels (DRLs) for medical radiodiagnostic examination
is required and recommended by international organizations
and by local national legislation [1–4]. Two national patient
dose surveys for establishing and updating National Diagnostic Reference Levels (NDRLs) have been performed in
Bulgaria so far [5, 6]. Third National Patient Dose Survey
(TNS) started by National Centre of Radiobiology and
Radiation Protection (NCRRP) in 2016 with non-financial
support from Ministry of Health (MoH) and regional
Departments of Radiation Hygiene (DRH) to the Regional
Health Inspectorates (RHI) under the umbrella of MoH,
based in 5 of the main cities in the country. In fulfilment of
this task, NCRRP has developed web-based platform and a
set of standard paper forms and instructions for data collection [5–7].
2
Materials and Methods
Methods for elaboration of NDRLs for different anatomic
locations and measurements of patient doses during TNS are
based on the “Recommendations and Guidance for use of
Diagnostic Reference Levels in Radiology” and “National
protocol for measurement methods of patient doses in X-ray
Diagnostics” respectively [8, 9]. Some of the available
International recommendations for elaboration of NDRLs
were taken into account also [1–3]. According to the chosen
methodology patient dose data from at least 20 X-ray systems should be used for each projection or examination for
establishing a DRL. A sample of at least 20 standard sized
adult patients should be collected for each standard projection or examination on each X-ray system. The personal
patient weight should lie in interval of 50–90 kg with an
average of 70 ± 3 kg. The Typical Dose (TD) for each
standard projection is being calculated as an arithmetic mean
© Springer Nature Singapore Pte Ltd. 2019
L. Lhotska et al. (eds.), World Congress on Medical Physics and Biomedical Engineering 2018,
IFMBE Proceedings 68/2, https://doi.org/10.1007/978-981-10-9038-7_7
33
34
of the relevant dosimetric quantity for the sample of patients.
This approach was chosen, since TNS was designed and
started in 2016 prior to the official publication of new recommendations of International Commission of Radiological
Protection (ICRP), as well as for purposes of easier comparison with previous national and international studies
performed so far [1, 10–12]. For children slightly different
approach based on median value of dosimetric quantity for
the sample of patients is employed for elaboration of typical
dose on each X-ray system in accordance with European
Guideline [13].
Bulgarian guidance as well as foreign protocols recommends that for adult patients NDRL shell be defined closer
to the third quartile of distribution of the typical doses
estimated for each projection, examination or procedure.
A national patient dose database build on MS Access was
elaborated and employed for storing, processing and analysing of collected data [14].
A. Dimov et al.
For mammography the reported parameters are: tube
potential (kVp); target/filter combination; exposure tube
current and time product (mAs); half value layer (HVL);
tube output (µGy/mAs); optical density (OD for film-screen
systems); source to breast support distance (mm) and patient
data. In the mammo quality control tests measurements of
incident air kerma (IAK) was also implemented. Incident air
kerma is the air kerma from the incident beam on the central
x-ray beam axis at the focal-spot-to surface distance at the
skin entrance plane. The average absorbed dose in the
glandular tissue in a uniformly compressed breast
(AGD) can be determined by first getting the IAK measurements on the standardized 45 mm PPMA phantom and
standard breast. In TNS AGD is calculated according to the
method recommended by the EUREF European guidelines
for quality assurance in mammography screening [16].
AGD is derived by calculation using the following
formula:
AGD ¼ IAK g c s,
2.1 Organization and Data Collection During
Third National Survey
Four methods of data collection have been employed:
A. Using internet based platform for automatic sending:
www.drl-bg.com [6];
B. Via electronic tables sent by e-mail to the electronic
address of the survey: rzmo@ncrrp.org;
C. Via paper hard copy by post mail;
D. Via information on local typical doses defined in Health
Establishments.
All information including terms and conditions for data
collection and submission was made available on web page
of the TNS [7]. On this web page following information is
available for download on both MS Excel and Adobe
Acrobat format files: a Short and a Full Instruction for data
collection; all necessary forms for registering of X-ray systems properties and patient dose registration forms for all
types of Diagnostic Radiology Examinations. These forms
include patient’s anthropomorphic data; main exposure
parameters; dosimetric quantities recommended by
IAEA TRS 457 and ICRP: measured Kerma Area Product
(KAP); displayed dose index in case of Computed Tomography (CT): CTDIw, CTDIvol or DLP [1, 15]. The web page
has also a link to the on-line platform for registering of
patient doses for those sites, which do prefer to use this
method of data submission to NCRRP [6]. Calls to the
Health Institutions to participate in TNS were published on
the web page of TNS as Circular Letters of the Director of
NCRRP and the Minister of Healthcare [5, 7].
ð1Þ
recommended by European protocols and IAEA TRS 457
Code of Practice [15]. Mammography dose survey included
33 X-ray systems: 17 in hospitals and 16 in Ambulances or
in smaller Medical Centres. Different systems were equipped
with different detectors: 20 X-ray units with Film Screen
Combinations (FSC); 5 with Computed Radiography
(CR) plates and 6 with a Direct Digital Radiography
(DDR) detector.
3
Results
A total number of 10,565 patient dose records from 91
Health Establishments were collected at NCRRP, as corresponding numbers per modality were as follows: 5731;
1793; 1100; 1237; 704, for: Radiography; Computed
Tomography (CT); Mammography; Interventional Cardiology and Fluoroscopy respectively. Those data comprised
195 X-ray systems distributed as follows: 81% in Hospitals
and 19% in Ambulances and smaller Medical Centres. 58 of
the X-ray units were situated in the Capital—Sofia, 41 in
bigger cities and 96 in middle and small size cities. About
67% of patient dose data were submitted via e-mail and
about 22% by post mail on paper—via above mentioned
methods B and C respectively. Submission of data via input
in the web based system (Method A) appeared to be not a
popular choice for Health establishments participated in
TNS, although it was highly recommended by MoH and
NCRRP as the primary submission choice. Submission of
information on local typical doses elaborated in Health
Establishments (Method D) appeared to be not a preferred
choice either. Such dosimetric data were collected mainly for
Elaboration of New NDRLs as Part of Third …
35
Table 1 NDRLs values from TNS and SNS given in KAP (lGy m2) for radiography projections and fluoroscopy Ba examinations
Chest PA
Abd AP
LS AP
LS Lat
Pelv AP
TS AP
TS Lat
Skull AP
Skull Lat
Ba enema
Ba meal
TNS
45
300
240
360
230
110
220
80
75
1840
1570
SNS
40
–
300
400
400
–
–
4000
1800
Table 2 NDRLs values from TNS, SNS and other NDRLs for ca and PCI given in KAP (lGy m2)
Survey
TNS
SNS
CA
4600
4000
PCI
13400
14000
EU
IE, 2009
6000
5310
AU, 2014
5865
3600
UK, 2010
–
8400
12900
4000
Table 3 NDRLs values from TNS, SNS and EU for CT of head, chest, abdomen and lumbar spine given in DLP (mGy cm), Cw (mGy) and Cvol
(mGy)
Head
TNS
Chest
Abdomen
Lumbar spine
DLP
Cvol
Cw
DLP
Cvol
Cw
DLP
Cvol
Cw
DLP
Cvol
Cw
1000
60
80
500
16
18
470
18
17
580
20
19
SNS
1000
–
60
550
–
25
600
–
30
–
–
–
EU
1000
60
–
400
10
–
800
25
–
500
35
–
Table 4 Third quartile values for AGD and ESAK obtained at phantom and patients studies at TNS and NDRLs obtained from SNS
Patients
Phantom
Phantom
AGD (mGy)
3-rd quartile
ESAK (mGy)
2.4
SNS NDRL
2.3
12
2.3
12
Table 5 Preliminary NDRLs from TNS for paediatric radiography of chest
0–1 years old
1–5 years old
5–10 years old
10–15 years old
8
10
16
2
KAP (µGy m )
TNS
6
mammography units with assistance and input from an
external medical physics group providing quality control
(QC) service to most of mammography systems participated
in TNS.
NDRLs obtained from TNS and SNS for
Anterior-Posterior (AP), Posterior-Anterior (PA), or Lateral
(Lat) Radiography projections of: Chest; Abdomen (Abd);
Lumbar Spine (LS); Pelvis (Pelv); Thoracic Spine (TS);
Skull (SK); as well as Fluoroscopy Barium (Ba) Contrast
studies are shown in Table 1 [6]. Respective data for Coronary Angiography (CA) and Percutaneous Coronary
Intervention (PCI) obtained from TNS, SNS, European
(EU) and some foreign surveys are shown in Table 2 [6, 10].
NDRLs for CT given in DLP (mGy cm), CTDIw (Cw)
(mGy) and CTDIvol (Cvol) obtained from TNS, SNS and EU
study are shown in Table 3 [6, 10].
Table 4 shows calculated AGD and ESAK from Phantom
and AGD from Patient mammography exposure data. Last
are recommended as NDRLs for mammography.
Preliminary NDRLs for paediatrics in frame of TNS are
obtained for Chest X-ray radiography projection only. Their
values are displayed at Table 5.
A more complete set of tables with detailed statistics can
be obtained from the author.
4
Discussions
Most values of Bulgarian NDRLs determined during TNS
for Radiography projections and Fluoroscopy Barium Contrast studies are closer to other European countries NDRLs
with exception for Chest PA [12]. Higher NDRL for
36
A. Dimov et al.
Chest PA is mainly due to commonly used non-optimal
“soft” technique with potential of the tube significantly
lower than recommended along with anti-scatter grid put
always in place which is a commonly observed practice [17].
Differences in SNS and TNS results are due mainly to
change in equipment technology of X-ray imaging systems
in place. Decrease in NDRLs is observed in all examinations
with an exceptions for CA. Increase in NDRL value for this
examination is explained with smaller and not so representative patient samples in SNS in comparison with TNS.
For PCI for example, this trend is not valid and during TNS
we obtained lower then SNS value as a NDRL [11].
Difference in NDRL values for AGD obtained from
phantom and patient exposure data is related probably to
lack of precise information for Anode-Filter combinations
on some of X-ray systems in study, which decreased the
number of systems included in Phantom based AGD
assessment.
The smaller proportion of patient data submitted by the
health establishments using the “on-line data collection
platform” (Method A.) might be related to its present user
interface design and a need for its further development,
improvement and promotion.
5
Conclusions
Third national patient dose survey collected significantly
bigger amount of data than first and second national surveys
and hence appeared to be more representative for the
country. NDRLs are determined for more Diagnostic Radiology Examinations. Successful realization of TNS became
possible due to joint efforts of NCRRP staff, active
involvement of Radiation control departments of Regional
Health Inspectorates (RHI), medical physicist and other
responsible staff in the health establishments in the country
and principal support from Management of NCRRP and the
Ministry of Health.
Conflict of Interest The authors declare that they have no conflict of
interest.
Statement of Informed Consent Informed consent was obtained from
all individual participants included in the study.
Protection of Human Subjects and Animals in Research All procedures performed in studies involving human participants were in
accordance with the ethical standards of the institutional and/or national
research committee and with the 1964 Helsinki declaration and its later
amendments or comparable ethical standards.
References
1. Diagnostic reference levels in medical imaging. ICRP Publication
135. Ann. ICRP 46(1) (2017).
2. Radiation protection and safety of radiation sources: International
basic safety standards. IAEA safety standards series No. GSR Part
3. IAEA, Vienna (2014).
3. Council Directive 2013/59/Euratom of 5 December 2013 laying
down basic safety standards for protection against the dangers
arising from exposure to ionising radiation, and repealing Directives
89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom
and 2003/122/Euratom. Official Journal of the European Union, L
13, 17 January 2014, 1–73 (2013). ISSN 1977-0677.
4. Ordinance N.o30 of the Ministry of Health for protection of
individuals at medical exposure, promulgated in State Gazette №
91 of November 15 (2005) (in Bulgarian).
5. Vassileva J, Dimov A, at al. Bulgarian experience in the
establishment of reference dose levels and implementation of a
quality control system in diagnostic radiology. Radiation Protection Dosimetry, Vol. 117, No. 1–3, 131–134 (2005).
6. Vassileva J., Ingilizova K. Dimov A., et al. National survey of
patient doses in diagnostic and interventional radiology and
nuclear medicine 2002–2013. NCRRP, Sofia (2013), ISBN:
978-619-90135-4-0.
7. Karadjov, A. Dimov, A. Vassileva, J. Anatschkowa, E. Recommendations and guidance for the use of the diagnostic reference
levels in radiology. EC Phare Project: Radiation protection and
safety in medical use of ionising radiation, Reference Number:
BG/2000/IB/EN 01–05, National Centre of Radiobiology and
Radiation Protection, Bulgaria (2003).
8. Karadjov, A. Dimov, A. Vassileva, J. Anatschkowa, E. Protocol on the
methods for patient dose measurements in x-ray diagnostics. EC Phare
Project: Radiation protection and safety in medical use of ionising
radiation, Reference Number: BG/2000/IB/EN 01–05, National Centre
of Radiobiology and Radiation Protection, Bulgaria (2003).
9. European Guidelines on DRLs for Paediatric Imaging. Final
complete draft (2016) (in press), available online at: http://www.
eurosafeimaging.org/wp/wp-content/uploads/2014/02/EuropeanGuidelines-on-DRLs-for-Paediatric-Imaging_Revised_18-July2016_clean.pdf, last accessed: 2017/09/02.
10. European Commission. Radiation Protection N 180. Diagnostic
Reference Levels in Thirty-six European Countries: Part 2/2.
Directorate-General for Energy, Directorate D - Nuclear Safety &
Fuel Cycle, Unit D3 — Radiation Protection (2014).
11. Dimov A, Ivanova D, at al. Design, methodology and purposes of
the third national patient dose survey in diagnostic radiology.
Scientific works of the union of scientists in Bulgaria – Plovdiv.
Series G. Medicine, Pharmacy and Dental Medicine, Vol. XIX,
House of Scientists, Plovdiv (2016). ISSN 1311 – 9427.
12. Vassileva J., Simeonov F., at al. On-line data collection platform
for national dose surveys in diagnostic and interventional radiology Radiation Protection Dosimetry 165 (1–4): 121–124 (2015).
13. National Centre for Radiobiology and Radiation Protection. Web
page of National Survey DRL2016. URL: http://www.ncrrp.org/
new/bg/DRL2016-c437, last accessed on 2017/11/25.
14. European Communities. European guidelines for quality assurance
in breast cancer screening and diagnosis. Fourth edition Supplements. Luxembourg: Office for Official Publications of the
European Communities (2013).
Elaboration of New NDRLs as Part of Third …
15. TECHNICAL REPORTS SERIES No. 457. Dosimetry in diagnostic radiology: an international code of practice. International
Atomic Energy Agency, Vienna (2007), ISBN 92–0–115406–2.
16. Dimov A., Simeonov F., Tsanev I., at al. National patient dose
surveys of chest radiography: 2002–2017. Is radiology practice in
37
the country optimized? Roentgenologia & Radiologia (in
manuscript).
17. Tsanev IM, Dimov AA. (2016) National database for patient dose
registration and analysis in diagnostic radiology. In: Proceedings
of 12-th National medical physics and biomedical engineering
conference-NMPEC, pp. 51–60. Sofia (2016).