CT dose reconstruction based on RIS and PACS data

www.nrpa.no

CT dose

reconstruction

based on RIS

and PACS data

Hilde M. Olerud. Dr.ing. Head of section, NRPA

1. 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?

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

– CTDI_vol 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?

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 transmitted radiation 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 -ra y b ea_m in x y p la ne Det ecto rs in xy plan e Continues scan

www.nrpa.no

CT coordinate system

x

y

Fan beam

z

Narrow beam –

Cone beam

MDCT

NxT

www.nrpa.no

Measurment of CT dose index,

CTDI

₁₀₀

IEC 32 cm phantom, 10 cm chamber and electrometer

∫

×

=

K

(

z

)

dz

T

N

1

CTDI

CTDI

D

z

www.nrpa.no

Current dosimetry in CT

ICRU REPORT 74 www.msct.eu

( )

z

dz

K

T

N

1

C

CTDI

∫

×

=

=

C

3

2

C

3

1

C

CTDI

=

=

⋅

+

⋅

T

N

d

factor

pitch

CT

×

Δ

=

factor

pitch

CT

/

C

factor

pitch

CT

/

CTDI

CTDI

=

=

L

CTDI

DLP

=

×

CTDI

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 CTDI_vol and the dose length product, DLP

• ALL these parameters are recorded as part of DICOM

Radiography and fluoroscopy _Mammography CT

DAP MGD D_air CTDI_w CTDI_vol DLP ESD

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

w

⋅

H

ORGAN/TISSUE

_w

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

w

= 1.00

ICRP revised 2007

w

is tissue weighting factors

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.htm

Input parameters

•

Scanner model

•

kV

•

Head/body FOV

•

Scan region

•

mA og rotation time

•

”collimation”

•

Pitch

The calculation of

•

Organ doses

•

CTDI

– CTDI

•

DLP –

effective dose

Scanner Model: Acquisition Parameters:

Manufacturer: mA 300 mA

Scanner: Rotation time 0.8 s

kV: mAs / Rotation 240 mAs

Scan Region: Collimation mm

Data Set MCSET05 Slice Width 5 mm

Current Data MCSET05 Pitch 1.5

Scan range Rel. CTDI 1.02 at selected collimatio

Start Position 0 cm CTDI (air) 19.1 mGy/100mAs

End Position 43 cm CTDI (soft tissue) 20.4 mGy/100mAs

Patient Sex: f nCTDIw 5.3 mGy/100mAs

Organ wT HT wT.HT Remainder Organs HT

Gonads 0.2 9.364 1.873 Adrenals 8.461

Bone Marrow (red) 0.12 4.371 0.525 Brain 0.001

Colon 0.12 9.059 1.087 Upper Large Intestine 10.797

Lung 0.12 1.135 0.136 Small Intestine 10.086

Stomach 0.12 11.190 1.343 Kidney 12.712

Bladder 0.05 11.239 0.562 Pancreas 8.234

Breast 0.05 0.317 0.016 Spleen 10.530

Liver 0.05 10.240 0.512 Thymus 0.249

Oesophagus (Thymus) 0.05 0.249 0.012 Uterus 9.722

Thyroid 0.05 0.021 0.001 Muscle 5.240

Skin 0.01 4.950 0.049

Bone Surface 0.01 6.532 0.065 CTDIw (mGy) 12.6

Kidneys 0.025 12.712 0.318 CDTIv ol (mGy) 8.4

Remainder 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 SØR v/ kvalitetsradiograf Berta Lohne

ImPACT CT Patient Dosimetry Calculator

version 0.99m, 1/07/2002

Scan Description / Comments

Update Data Set

GE

GE HiLight, HiSpeed, CT/i (No SmB) 120

Body

Look up

Get From Phantom Diagram

5

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

With and without contrast With contrast

Without contrast

CT head/brain: suspected tumour/metastase

Effective 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) Antall scannere

With and without contrast With contrast

Without contrast

CT head/brain : hemorrhage versus thromboses/emboli

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

www.nrpa.no

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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

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

• CTDI_vol

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

www.nrpa.no

The 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)

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

IHE

profile

www.nrpa.no

The 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

ƒ IHE North America Connectathon 2011 - January 17-21, Chicago (USA)

ƒ IHE-Europe Connectathon 2011 - April 11-15, Pisa (Italy).

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

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

[email protected]

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 _coho rt is c reated _from RIS th_{e ca} lculate_{d dose} s ca_n be allo cated _indivi dual ch ildren _base d on 1 993 s ite info

www.nrpa.no

EPI-CT: Estimates of organ doses in pediatric CT

Cohort of children found 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

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

www.nrpa.no

Effective dose from CT examinations 2002 –

2008

country mean values from national surveys ADULTS

CT exam Effective dose mSv

2002 Effective dose mSv 2008 Change mSv 2002-2008 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 doses

CT 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 development standardisation

QA,

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

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

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

www.nrpa.no

100mm active length

CT –ion chamber

0,3 mm active lenght

CT-SD16 solid state detector

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

www.nrpa.no

Size specific dose

estimates

•

Provide a method to

estimate CTDI

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

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