www.nrpa.no

CT dose reconstruction based on RIS and PACS dataHilde M. Olerud. Dr.ing.Head of section, NRPA1. Amanuensis II UiO, Inst. of Physics

Hiii, if you understand the

technology you may understand the CT dosimetry also...

Pst, Urvin, what can I say about CT

dosimetry?20 min

www.nrpa.no

What I would like to talk about….

•

Principle of CT–

Registration –

Reconstruction –

Imaging

•

Energy deposit in patient during CT scanning•

Practical dose quantities monitored in i CT–

CTDIvol

and DLP–

ICRU’s new concepts of CT dosimetry

•

Calculation of organ doses

and effective dose–

MC simulations, Conversion factors, Available software

•

Norwegian CT dose surveys–

Dose data available for adults and pediatric patients

•

What do we find in RIS and what in PACS?–

How to estimate organ doses for pediatric patients

www.nrpa.no

Computed Tomography (CT) GIVES TRANSVERSIAL RECONSTRUCTED SLICES

• REGISTRATION The X-ray tube is rotating around the patient who is irradiated with a fan beam. The detectors registrates the transmittedradiation through different body parts• RECONSTRUCTION By interpolation and filtered backprojection the computer reconstructs transversal slices of the volume of interest and enhance small differences in density between tissues and organs• IMAGE VIEWING The pixels are given shades of grey or colours depending of X-ray density. Contrast may be manipulated by window settings (WL and WW). The pixel information may be transferred to workstation for processing.

X-ray tube

X-ray beam in xy plane

Detecto

rs in

xy pl

ane

Continues scan

www.nrpa.no

CT coordinate system

xy

Fan beam

z

Narrow beam –

Cone beam

MDCT

NxT

Tomographic plane Longitudinal direction

www.nrpa.no

Measurment of CT dose index,

CTDI100

IEC 32 cm phantom, 10 cm chamber and electrometer

∫+

−×=

mm50

mm50a100 dz)z(K

TN1CTDI

CTDI

Dmax

NxT

zLongitudinal direction

www.nrpa.no

Current dosimetry in CT ICRU REPORT 74 www.msct.eu

( )dzzKTN

1CCTDI aKa ∫+∞

∞−×==

p,100,PMMA,Kc,100,PMMA,Kw,PMMA,Kw C32C

31CCTDI ⋅+⋅==

TNdfactorpitchCT×Δ

=

factorpitchCT/CfactorpitchCT/CTDICTDI w,PMMA,Kwvol ==

LCTDIDLP vol ×=

CTDI100, c

CTDI100, p 1 cm

www.nrpa.no

The “practical dose parameters”

recorded

•

For radiography and fluoroscopy the practical dose parameter is the dose area product, DAP,•

for mammography it is the calculated “mean glandular dose”, MGD,•

while for CT it is the weighted and pitch corrected CTDIvol

and the dose length product, DLP•

ALL these parameters are recorded as part of DICOM

Radiography and fluoroscopy Mammography CT

DAP

MGD

Dair

CTDIwCTDIvolDLPESD

Effective dose, ICRP 1990• Various organs and tissue are exposed

differently during an X-ray examination• Various organs and tissues have different

sensitivity to radiation• Think of a dose, if given to the whole body,

would result in the same stochastic risk, as if you exposed a part of the body for a higher dose

• This calculated dose is called ”effective dose”, and is given in units of sievert (Sv)

• Effective dose is the sum of doses given to selected ICRP organs, weighted accounting for the organ sensitivity to radiation

E = Σ wT ⋅ H T

ORGAN/TISSUE wT Gonades 0.20 Red bone marrow Colon Lung tissue Stomack

0.12 0.12 0.12 0.12

Bladder Breasts Liver Oesophagus Thyroid

0.05 0.05 0.05 0.05 0.05

Skin Bone

0.01 0.01

Rest 0.05 Σ wT = 1.00

ICRP revised 2007

wT

is tissue weighting factors HT

is the equivalent dose to organ

www.nrpa.no

The basis for organ dose assessments in CT

•

A number of radiation protection organisations around the world have performed Monte Carlo simulations

for a large number of types of x-ray

examination under a range of exposure conditions and published organ and effective dose conversion coefficients to be integrated in software

”Freeware”

Dose calculators for CT :•

Impact http://www.impactscan.org/index.htm

•

CT-Expo http://www.mh-hannover.de/kliniken/radiologie/str_04.html

Voxel phantom series B created at the University of Florida.

Oak Ridge National Laboratory

Cristy and Eckerman, 1987

www.nrpa.no

CT dose calculator ADULTS

http://www.impactscan.org/index.htmInput parameters•

Scanner model

•

kV•

Head/body FOV

•

Scan region•

mA og rotation time

•

”collimation”•

Pitch

The calculation of•

Organ doses

•

CTDIw

– CTDIvol

•

DLP –

effective dose

Scanner Model: Acquisition Parameters:Manufacturer: mA 300 mAScanner: Rotation time 0.8 skV: mAs / Rotation 240 mAsScan Region: Collimation mmData Set MCSET05 Slice Width 5 mmCurrent Data MCSET05 Pitch 1.5Scan range Rel. CTDI 1.02 at selected collimatioStart Position 0 cm CTDI (air) 19.1 mGy/100mAsEnd Position 43 cm CTDI (soft tissue) 20.4 mGy/100mAsPatient Sex: f nCTDIw 5.3 mGy/100mAs

Organ wT HT wT.HT Remainder Organs HT

Gonads 0.2 9.364 1.873 Adrenals 8.461Bone Marrow (red) 0.12 4.371 0.525 Brain 0.001Colon 0.12 9.059 1.087 Upper Large Intestine 10.797Lung 0.12 1.135 0.136 Small Intestine 10.086Stomach 0.12 11.190 1.343 Kidney 12.712Bladder 0.05 11.239 0.562 Pancreas 8.234Breast 0.05 0.317 0.016 Spleen 10.530Liver 0.05 10.240 0.512 Thymus 0.249Oesophagus (Thymus) 0.05 0.249 0.012 Uterus 9.722Thyroid 0.05 0.021 0.001 Muscle 5.240Skin 0.01 4.950 0.049Bone Surface 0.01 6.532 0.065 CTDIw (mGy) 12.6Kidneys 0.025 12.712 0.318 CDTIv ol (mGy) 8.4Remainder 2 0.025 5.191 0.130 DLP (mGy.cm) 361.2

Total Effective Dose (mSv) 6.629

CT Bekken/abdomen ved Lab 2, Indre enfold, HF SØRv/ kvalitetsradiograf Berta Lohne

ImPACT CT Patient Dosimetry Calculatorversion 0.99m, 1/07/2002

Scan Description / Comments

Update Data Set

GEGE HiLight, HiSpeed, CT/i (No SmB)120Body

Look upGet From Phantom Diagram

5

Look up

www.nrpa.no

Effective dose for 7 typical CT exams in 90ties RESULTs BASEDT ON 49 LABORATORIES

Olerud, HM. Radiat Prot Dosim 1997;71(2):123-133

•

NRPB -

SR250 phantom and conversion factors–

Scanner model, kV, mAs, slice thickness, increment, CTDI, scan length

•

CTDOSE software for calculations of effektive dose•

New scanners: http://www.impactscan.org

CT examination E (mSv) Country mean

E (mSv) median

E (mSv) 3. quartile

Max/Min value

Head/brain 2,0 1,8 2,7 8,0 Thorax 11,5 10,0 15,5 19,5 Abdomen 12,8 9,9 17,2 13,3 Lumbal spine 4,5 4,4 5,2 10,5 Liver 11,9 11,1 16,4 8,7 Kidneys 9,9 10,1 14,4 19,7 Pelvis 9,8 8,3 11,8 17,2

www.nrpa.no

Variation in CT doses in Norway

•

www.nrpa.no

publikasjoner/Strålevernrapport 11:1995: "Computer tomografi ved norske sykehus. Undersøkelsesteknikk og stråledose til pasient”

www.nrpa.no

Explanations for dose variation COMPUTED TOMOGRAPHY

•

The difference in scanner technology (manufacturer, model)•

Examination protocol (scan volume, use of contrast, mAs)

•

Clinical question

0

1

2

3

4

5

6

7

0,5 1

1,5 2

2,5 3

3,5 4

Effektiv dose (mSv)

Ant

all s

cann

ere

With and without contrastWith contrastWithout contrast

CT head/brain: suspected tumour/metastaseEffective dose 2.4 mSv (mean)

0

2

4

6

8

10

12

0,5 1

1,5 2

2,5 3

3,5 4

Effektiv dose (mSv)

Ant

all s

cann

ere

With and without contrast

With contrastWithout contrast

CT head/brain : hemorrhage versus thromboses/emboliEffective dose 1.6 mSv (mean)

www.nrpa.no

Exposure of the lense of the eyes COMPUTED TOMOGRAPHY

•

May be considerable when repeating CT examinations of the head/brain for follow-up reasons/chronic ill patients

–

Ex. Children with hydrocephalus treated

with shunt• Dependent of the tilt of the gantry

Lense doses (mGy)

Parallel with scull basis

axiale slices

Mean Min Max

3.9 1.1 9.4

80.9 39.1 108.6

ICRP threshold values :•

Measurable changes in lenses 0.5 -

2 Gy

•

Cataract

2 -

10 Gy

www.nrpa.no

Patient ID

age/sex

Clinical question

Examination

Codes

Scan

parameters

Dose

parameters

Images

RiS and PACS a chest of treasures

•

Frequencies of examinations•

Dosedata as defined by DICOM/IEC/IHE profil

•

Gathered from RIS or DICOM/PACS to electronic patient journal or central databases for statistics

RiS/PACS

www.nrpa.no

IEC/DICOM standards for dose reporting in CT

•

When ordering a new examination the agreed dose quantities are

popping up on the operators consol

•

CTDIvol

A measure of the average dose

deposit in a slice–

when the whole organ is covered by the primary scan volume, it is also a measure of the organ dose

•

DLP A measure of the total energy

imparted during the whole examination

•

Desired that the dose parameters are recorded in the patient journal

www.nrpa.noThe work in IEC, DICOM and IHE ... – 09/06/2011 17/15

Dose reporting evolution

•

To overcome limitations of DICOM header, a work was undertaken by DICOM in collaboration with IEC to register, separately from the images, dosimetric and related data.

•

This work led to the creation in 2004 of a DSR (Dose Structured Report) to capture and collect all information dedicated to dosimetry.

•

The DSR contains a set of individual Irradiation Event (IE) which contains the relevant technical and dosimetric details for one single continuous irradiation. Whether or not the images are stored, IE

and DSR are registered.

•

Two Dose SR exist:•

Supplement 94: Diagnostic X-Ray Radiation Dose Reporting (2005)

•

Supplement 127: CT Radiation Dose Reporting (2007)

www.nrpa.no

The new IHE profile was tested in 2009 Integrating the Healthcare Enterprise http://www.ihe.net/

X-ray equip.•GE•Philips•Siemens•Toshiba•xx•yy

RiS/PACS•Agfa•Fuji•Kodak•Sectra•Siemens•aa•bb

IHEprofile

Now everybody’s talking !

www.nrpa.noThe work in IEC, DICOM and IHE ... – 09/06/2011 19/15

IHE REM Profile status (info from IRSN, France)

During Connectathons IHE provides a detailed implementation and testing process to promote the adoption of standards-based interoperability by vendors and users of healthcare information systems.

▌ In 2011 the REM profile was tested at two Connectathons:IHE North America Connectathon 2011 - January 17-21, Chicago (USA)IHE-Europe Connectathon 2011 - April 11-15, Pisa (Italy).

▌The first REM Profile demo was presented at JFR’2009.

www.nrpa.no

Dose reconstruction based on PACS data

•

PerMos: Automatic calculation of organ doses based on PACS data –

Data from the DICOM-header is transferred, no images

–

Pseudonymization, no patient information leave the hospital–

Work on all PACS-systems from all manufacturers

•

Developed by Research Centre Henry Tudor, Luxembourg, www.tudor.lu

•

Based on new software NCICT: beta version available SEP 2011–

New pediatric phantoms, new MC simulations

www.nrpa.no

User can change the scan range by dragging upper and lower lines.

Organ/effective dose are presented here and automatically copied to clipboard. User can “paste”

into Excel spreadsheet or somewhere else.

Predefined scan range for different age phantoms are provided based on common scan protocol. Will be extended.

Scan start/end slice can be entered (e.g. 1 means 1 cm from the top of the head). Scan range bars will be automatically changed.

ED60 and ED103 are effective doses based on ICRP 60 and 103, respectively. “Splitting rule”

in ICRP 60 was applied.

User can select phantoms from newborn to adult male/female. Reference height and weight are provided but not editable.

User can select from four major manufacturers. The list of scanner models are changed depending on manufacturer.

User can select from head and body filters.

CTDIw normalized to 100 mAs will be displayed from

Choonsik Lee, PhD

National Cancer Institute, NIH, DHHS

Rockville MD 20852

leechoonsik@mail.nih.gov

NCICT β.v.

www.nrpa.no

Dose reconstruction based on RIS data TO ALLOCATE DOSE VALUES TO CHILDREN EXAMINAED BEFORE PACS

FROM RIS• Date• CT room/Hospital• Patient ID, i.e. AGE/SEX• Examination type

– hospital terminology • NORAKO codes• Clinical indication

• FROM PREVIOUS CT SURVEY 1993– 49 CT rooms

• CT manufacturer/Model•

Typical scan protocol for various

examination types ADULT–

head, thorax, abdomen, liver, kidney,

spine, pelvis– 12 clinical indications

• Assumption– adult protocols were used for pediatrics

•

Use new software, NCICT, to calculate organ doses

– for the protocols used at site in the 90thies– for all age groups/both sexes

When cohort is created from RIS the calculated doses can

be allocated individual children based on 1993 site info

www.nrpa.no

EPI-CT: Estimates of organ doses in pediatric CT

Cohort of childrenfound in RIS

Retrospective based on RIS•

NRPA will estimate organ

doses to children –

for CT scanners used in

the 90thies– for typical CT procedures– for different age/sex–

based on new software,

NCICT•

From the RIS cohort or

manual collected info– the name of the hospital– the CT scanner model– age/sex of the child– CT procedure

•

General dose values can be allocated to individuals

When PACS data available•

Automatic gathering of CT

scan parameters for individual patients by the program

PerMos–

From DICOM header the

scanner model, scan region,

FOV, kV, mA/rotation time,

collimation, pitch….–

New NCICT will calculate the

organ doses for individual

children

•

Individual dose values can be allocated to individuals

www.nrpa.no

New knowledge and spin-off from EPI-CT•

Organ doses in CT may exceed 50 mGy for adults–

Even higher for children previously

•

We are in the range epidemiological proofs of possible risks may be found–

the cohort has to be followed for a long time

•

National experience in use of new CT software and image quality phantoms

•

Automatic gathering of data from PACS/DICOM–

Can be used in all radiology for QC, optimisation and dose records

…… Thank you for the attension!

www.nrpa.no

Effective dose from CT examinations 2002 –

2008 country mean values from national surveys ADULTS

CT exam Effective dose mSv2002

Effective dose mSv2008

Change mSv2002-2008

Head/brain 1,8 1,5 -0,3

Neck 3,4 2,6 -0,8

Thorax 11,5 4,7 -6,8

Columna 4,3 5,6 +1,3

Abdomen 12,6 10 -2,6

Pelvis 9,3 7,3 -2

www.nrpa.no

Trends in CT dosesCT doses should increase because:•

”Overbeaming”

•

High spatial resolution claims more dose if the noise level in images are to be maintained

•

Larger scan volume per CT serie•

More fast CT series to follow different contrast phases

CT doses should decrease because:•

More sensitive detectors

•

Use of pitch>1 •

Tube current modulation/AEC

•

Focus on quality control and optimisation–

Development of new CT protocols is a multidisciplinary task –

The use of diagnostic reference levels (DRL’s)–

Regulations: authorization, inspection and audits

Technical developmentstandardisation

QA,regulation

www.nrpa.no

EU EPI-CT WP4 Dose reconstruction/Norway

•

RIS information alone may be used to establish estimates of the radiation doses in cases when PACS data are not available. This would increase the statistical power in the EPI-CT project.

•

NRPA have information of the range of CT scan parameters used during the 90’thies in Norway for adult patients. The national survey included 49 CT rooms, all vendors and scanner models in use at that time were represented (GE, Siemens, Thoshiba and Phillips).–

7 exam types, 12 indications

•

We could recalculate the paediatric organ doses using the NCI-CT (Choonsik Lee/National Cancer Institute/Rockville MD) software based on the range of known adult scan protocols, and provide this information to the EPI-CT project.

•

In the 90’thies adult protocols were more commonly used also for children, resulting in quite high organ doses. We may approximate that adult protocols were quite generally used

•

Good estimates of organ doses may be allocated to individual children having CT during the ninethies just based on RIS

www.nrpa.no

NCICT SEP 2011 mail•

Please go ahead with installing the software and begin the test.

I appreciate your comments and help to improve this tool.Your comment on the different CT scanner is exactly what we (together) need to deal with.

•

Currently, the organ dose provided from the NCICT is normalized to CTDIw of the Siemens Sensation 16 scanner which was actually modeled. To deal with other scanners, the NCICT is using the library of CTDIw for a total of

70 old and current CT scanners as you can see when you install the NCICT.

•

Looks like the scanner list you sent me is pretty much covered by the list I'm using. •

However, I definitely need to extend the library to cover more scanners. I plan to visit Dr. Paul Shrimpton at HPA UK to discuss this issue during the visit to Newcastle University to work on UK CT study with Mark Pearce. I also work with US FDA to extend the library.

•

Do you have any resources to help? I need CTDIw for head (16 cm)

and body (32 cm) phantoms for more CT scanners.

Choonsik Lee, PhD

National Cancer Institute, NIH, DHHS

Rockville MD 20852

leechoonsik@mail.nih.gov

choonsiklee@gmail.com

www.nrpa.no

EU EPI-CT WP7 Optimisation/Norway

•

The new ICRU phantom presented by John M.

Boone Chairman, ICRU committee on CT Image

Quality and Patient Dosimetry

•

Evaluates image quality (CNR, MTF) and dose

(z-sensitivity profile) in the same phantom, ends

the out of date concept of CTDI100

•

In collaboration with the partner in Luxembourg/Henry Tudor

–

Have this phantom

manufactured by PTW–

Develop software that

automatically evaluates image

quality and dose •

Scan it with current paediatric CT

protocols for the range of current CT scanner models

– Survey as input to EPI-CT WP7•

Compare results with results from

survey of clinical images using the same protocols

•

Input to further development of the phantom for paediatric use

John Boone [john.boone@ucdmc.ucdavis.edu]

www.nrpa.no

http://www.rti.se/products/barracuda/CT-SD16 CT Slice Detector

•

The CT-SD16 is based on solid-state technology, it is robust and it fits into existing standard phantoms used for CTDI measurements.

•

The CT-SD16 detectors are very thin (width 250 μm). Thanks to their small width, the detectors are completely irradiated when the table is moving and the CT scans over the probe.

•

The dose is measured in every point of the X-ray beam and the total dose profile is acquired regardless of how wide the beam is.

•

There is no limitation of the beam width due to limited length of the probe. This makes it possible to measure without the limitation of traditional probes:–

CTDI100–

CTDIvol–

CT dose profile–

Scan speed–

Performance of the AEC

www.nrpa.no

100mm active length

CT –ion chamber

0,3 mm active lenght

CT-SD16 solid state detector

Two approaches for CT dosimetry

www.nrpa.no

CT-slice probe collecting Dose profile based on manuel trig (Timed mode)

Only one measurement in the central hole is needed to collect data when using the CT-slice probe for routine QA.

CtDIw (mGy)DLP (mGycm)

Print

CtDIw (mGy)DLP (mGycm)

Print

CT-SD16 Program and application (RTI Electronics AB, Sweden)

www.nrpa.no

Size specific dose estimates

•

Provide a method to estimate CTDIvol

for individual patients based on–

Their circumference/ AP-lat dimensions

–

Conversion factors from measurements either related to 16cm or 32 cm phantoms

–

How to apply this report for measurements with the new ICRU 30cm phantom…?

–

For EPI-CT individual children…?

www.nrpa.no

Useful

links

•

ImPACT

Group, St. George’s Hospital, London: http://www.impactscan.org/

•

European Comission. Europrean guidlines on quality criteria for computed tomography. EUR 16262 EN (1999)

http://www.drs.dk/guidelines/ct/quality/index.htm The 2004 CT Quality

Criteria

http://www.msct.eu/CT_Quality_Criteria.htm

•

EU DOSE DATAMED prosjektene (2003 –

2007) & DDM2 (2011 –

2013) www.ddmed.eu

•

IAEA/IDOS symposium 8. –

12. Nov 2010 Vienna http://www-pub.iaea.org/mtcd/meetings/announcements.asp?confid=38093

John M. Boone, chair

ICRU committe

on

CT dosimetry

and image quality

•

http://www.nrpa.no•

http://www.uio.no/studier/emner/matnat/fys/FYS4760/index.xml

http:/ec.europa.eu/energy/nuclear/radioprotection/publication_en-htm