IEC 62985:2019

IEC 62985 ®
Edition 1.0 2019-09
INTERNATIONAL
STANDARD
Methods for calculating size specific dose estimates (SSDE) for computed
tomography
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IEC 62985 ®
Edition 1.0 2019-09
INTERNATIONAL
STANDARD
Methods for calculating size specific dose estimates (SSDE) for computed

tomography
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 11.040.50 ISBN 978-2-8322-7290-9

– 2 – IEC 62985:2019 © IEC 2019
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Verification of method used to calculate D (z) . 9
W
4.1 General . 9
4.2 Characteristics of the water PHANTOMS . 9
4.3 Characteristics of the anthropomorphic PHANTOM . 10
4.4 Generation of D (z) for the water PHANTOMS . 10
W,REF
4.5 Verification of D for the water PHANTOMS . 10
W,REF
4.6 Generation of D for the water PHANTOMS . 10
W,IMP
4.7 Verification of D (z) against D (z) for the water PHANTOMS . 11
W,IMP W,REF
4.8 Generation of D (z) for the anthropomorphic PHANTOM. 11
W,REF
4.9 Generation of D (z) for the anthropomorphic PHANTOM . 12
W,IMP
4.10 Verification of D (z) against D (z) for the anthropomorphic
W,IMP W,REF
PHANTOM . 12
5 Requirements and limitations . 12
5.1 Calculation of SSDE and D for CT SCANNERS and RDIMS . 12
W
5.2 Pre-scan display of SSDE for CT SCANNERs . 12
5.3 Post-scan updating of SSDE and D for CT SCANNERS . 12
W
5.4 Pre and post-scan display of SSDE and D for CT SCANNERS . 13
W
5.5 Post-scan recording of SSDE and D for CT SCANNERS . 13
W
5.6 Limitations of calculation and display of SSDE and D . 13
W
5.7 Requirements for identification of limitations in the ACCOMPANYING
DOCUMENTS . 13
5.8 Updating SSDE conversion factors, ƒ . 14
Annex A (normative) SSDE conversion factors . 15
A.1 Clarification regarding the use of effective diameter versus D . 15
W
A.2 Equation for determination of SSDE conversion factor . 15
Annex B (normative) Language regarding the general limitations of the SSDE
methodology for use in the ACCOMPANYING DOCUMENTS . 17
Annex C (informative) Estimates of the magnitude of uncertainties from special clinical
scenarios . 18
C.1 General . 18
C.2 Neck included in scanned anatomy . 18
C.3 Range of scan projection radiograph exceeded . 18
C.4 Single or bilateral extremities scanned . 18
C.5 PATIENT not positioned at the centre of rotation along the source/detector
direction . 19
C.6 PATIENT anatomy outside the scan field of view . 19
C.7 Foreign objects within the scanned projection radiograph or scan volume . 19
Bibliography . 20
Index of defined terms used in this document . 21

Figure A.1 – Visualization of ƒ(D ) versus D for the body and head parameters
w W
provided in Table A.1 . 16

Table 1 – Anthropomorphic PHANTOM regions to be scanned . 11
Table A.1 – SSDE Conversion factor as a function of D . 15
W
– 4 – IEC 62985:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
METHODS FOR CALCULATING SIZE SPECIFIC DOSE
ESTIMATES (SSDE) FOR COMPUTED TOMOGRAPHY

FOREWORD
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International Standard IEC 62985 has been prepared by subcommittee 62B: Diagnostic
imaging equipment, of IEC technical committee 62: Electrical equipment in medical practice.
The text of this International Standard is based on the following documents:
FDIS Report on voting
62B/1133/FDIS 62B/1144/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
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– requirements and definitions: roman type;

– informative material appearing outside of tables, such as notes, examples and references: in smaller type.
Normative text of tables is also in a smaller type;
– TERMS DEFINED IN CLAUSE 3, IN CLAUSE 3 OF IEC 60601-1:2005 AND
IEC 60601-1:2005/AMD1:2012, OF THE COLLATERAL STANDARDS, OF IEC TR 60788:2004 OR
AS NOTED: SMALL CAPITALS.
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implementation nationally not earlier than 3 years from the date of publication.
The contents of the corrigendum 1 (2022-06) have been included in this copy.

– 6 – IEC 62985:2019 © IEC 2019
INTRODUCTION
The SIZE SPECIFIC DOSE ESTIMATE (SSDE) is an estimate of the average ABSORBED DOSE to the
scan volume that takes into account the ATTENUATION of the anatomy being scanned (using
the WATER EQUIVALENT DIAMETER D ) and the RADIATION OUTPUT of the CT SCANNER (using
W
CTDI ).
VOL
SSDE is intended to provide a dose estimate for PATIENTs of all sizes. SSDE, which is given in
units of mGy, is especially important for small paediatric PATIENTS since the corresponding
applied level of RADIATION (CTDI , also given in units of mGy) does not adequately indicate
VOL
the absorbed RADIATION DOSE.
SSDE is calculated using a SSDE CONVERSION FACTOR AT LONGITUDINAL POSITION Z (ƒ) and the
...