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? 20 min
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CT dose reconstruction based on RIS and PACS data · CT dose reconstruction based on RIS and PACS data Hilde M. Olerud. Dr.ing. Head of section, NRPA. 1. Amanuensis II UiO, Inst.
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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
• 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
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CT coordinate system
xy
Fan beam
z
Narrow beam –
Cone beam
MDCT
NxT
Tomographic plane Longitudinal direction
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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
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Current dosimetry in CT ICRU REPORT 74 www.msct.eu
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
CT head/brain : hemorrhage versus thromboses/emboliEffective dose 1.6 mSv (mean)
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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
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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
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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
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.
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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–
• 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
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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!
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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
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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
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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
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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)
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:–