CT dose reconstruction based on RIS and PACS data

Transcription

1 Pst, Urvin, what can I say about CT dosimetry? 20 min CT dose reconstruction based on RIS and PACS data Hiii, if you understand the technology you may understand the CT dosimetry also... Hilde M. Olerud. Dr.ing. Head of section, NRPA 1. Amanuensis II UiO, Inst. of Physics

2 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? How to estimate organ doses for pediatric patients

3 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-ray beam in xy plane Continues scan Detectors in xy plane

4 CT coordinate system Fan beam Narrow beam Cone beam MDCT y x z NxT Tomographic plane Longitudinal direction

5 Measurment of CT dose index, CTDI 100 IEC 32 cm phantom, 10 cm chamber and electrometer Longitudinal direction z CTDI + 50 mm = K a ( z ) dz N T 50 mm CTDI D max NxT

6 Current dosimetry in CT ICRU REPORT 74 CTDI 100, c CTDI 100, p 1 cm CTDI a = C K = 1 N T + K a ()dz z CTDI w = CT pitch C K,PMMA,w factor = = 1 3 Δd N T C K,PMMA,100,c C K,PMMA,100,p CTDI vol = CTDI w / CT pitch factor = C K,PMMA, w / CT pitch factor DLP = CTDI vol L

7 The practical dose parameters recorded Radiography and fluoroscopy Mammography CT ESD DAP CTDI w CTDI vol DLP D air MGD 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

8 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 ORGAN/TISSUE w T Gonades 0.20 Red bone marrow 0.12 Colon 0.12 Lung tissue 0.12 Stomack 0.12 Bladder 0.05 Breasts 0.05 Liver 0.05 Oesophagus 0.05 Thyroid 0.05 Skin 0.01 Bone 0.01 Rest 0.05 Σ w T = 1.00 ICRP revised 2007 E = Σ w T H T w T is tissue weighting factors H T is the equivalent dose to organ

9 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 CT-Expo Oak Ridge National Laboratory Cristy and Eckerman, 1987 Voxel phantom series B created at the University of Florida.

10 CT dose calculator ADULTS ImPACT CT Patient Dosimetry Calculator version 0.99m, 1/07/2002 Scanner Model: Acquisition Parameters: Manufacturer: GE ma 300 ma Scanner: GE HiLight, HiSpeed, CT/i (No SmB) Rotation time 0.8 s kv: 120 mas / Rotation 240 mas Scan Region: Body Collimation 5 mm Data Set MCSET05 Update Data Set Slice Width 5 mm Current Data MCSET05 Pitch 1.5 Scan range Rel. CTDI Look up 1.02 at selected collimatio Start Position 0 cm Get From Phantom CTDI (air) Look up 19.1 mgy/100mas End Position 43 cm Diagram CTDI (soft tissue) 20.4 mgy/100mas Patient Sex: f nctdi w 5.3 mgy/100mas Organ w T H T w T.H T Remainder Organs H T Gonads Adrenals Bone Marrow (red) Brain Colon Upper Large Intestine Lung Small Intestine Stomach Kidney Bladder Pancreas Breast Spleen Liver Thymus Oesophagus (Thymus) Uterus Thyroid Muscle Skin Bone Surface CTDI w (mgy) 12.6 Kidneys CDTI vol (mgy) 8.4 Remainder DLP (mgy.cm) Total Effective Dose (msv) Input parameters Scanner model kv Head/body FOV Scan region ma og rotation time collimation Pitch The calculation of Organ doses CTDI w CTDI vol DLP effective dose Scan Description / Comments CT Bekken/abdomen ved Lab 2, Indre enfold, HF SØR v/ kvalitetsradiograf Berta Lohne

11 Effective dose for 7 typical CT exams in 90ties RESULTs BASEDT ON 49 LABORATORIES CT examination E (msv) E (msv) E (msv) Max/Min value Country mean median 3. quartile 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 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: Olerud, HM. Radiat Prot Dosim 1997;71(2):

12 Variation in CT doses in Norway publikasjoner/strålevernrapport 11:1995: "Computer tomografi ved norske sykehus. Undersøkelsesteknikk og stråledose til pasient

13 Explanations for dose variation COMPUTED TOMOGRAPHY The difference in scanner technology (manufacturer, model) Examination protocol (scan volume, use of contrast, mas) Clinical question Antall scannere CT head/brain: suspected tumour/metastase Effective dose 2.4 msv (mean) ,5 1 1,5 2 2,5 3 3,5 4 Effektiv dose (msv) With and without contrast With contrast Without contrast CT head/brain : hemorrhage versus thromboses/emboli Effective dose 1.6 msv (mean) Antall scannere ,5 1 1,5 2 2,5 3 3,5 4 Effektiv dose (msv) With and without contrast With contrast Without contrast

14 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) Mean Min Max Parallel with scull basis axiale slices ICRP threshold values : Measurable changes in lenses Gy Cataract 2-10 Gy

15 RiS and PACS a chest of treasures RiS/PACS Patient ID age/sex Clinical question Examination Codes Scan parameters Dose parameters Images 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

16 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 are recorded in the patient journal

17 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) The work in IEC, DICOM and IHE... 09/06/ /15

18 The new IHE profile was tested in 2009 Integrating the Healthcare Enterprise X-ray equip. GE Philips Siemens Toshiba xx yy IHE profile RiS/PACS Agfa Fuji Kodak Sectra Siemens aa bb Now everybody s talking!

19 IHE REM Profile status (info from IRSN, France) The first REM Profile demo was presented at JFR In 2011 the REM profile was tested at two Connectathons: IHE North America Connectathon January 17-21, Chicago (USA) IHE-Europe Connectathon April 11-15, Pisa (Italy). 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. The work in IEC, DICOM and IHE... 09/06/ /15

20 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, Based on new software NCICT: beta version available SEP 2011 New pediatric phantoms, new MC simulations

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

22 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 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

23 EPI-CT: Estimates of organ doses in pediatric CT 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 Cohort of children found in RIS 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

24 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!

25 Effective dose from CT examinations country mean values from national surveys ADULTS CT exam Effective dose msv Effective dose msv Change msv 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

26 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 Technical development standardisation 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 QA, regulation

27 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

28 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 [email protected] [email protected]

29 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 CTDI 100 John Boone 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

30 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

31 Two approaches for CT dosimetry 100mm active length 0,3 mm active lenght CT ion chamber CT-SD16 solid state detector

32 CT-SD16 Program and application (RTI Electronics AB, Sweden) Only one measurement in the central hole is needed to collect data when using the CT-slice probe for routine QA. CT-slice probe collecting Dose profile based on manuel trig (Timed mode) CtDIw (mgy) DLP (mgycm) Print

33 Size specific dose estimates Provide a method to estimate CTDI vol 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?

34 Useful links ImPACT Group, St. George s Hospital, London: European Comission. Europrean guidlines on quality criteria for computed tomography. EUR EN (1999) The 2004 CT Quality Criteria EU DOSE DATAMED prosjektene ( ) & DDM2 ( ) IAEA/IDOS symposium Nov 2010 Vienna John M. Boone, chair ICRU committe on CT dosimetry and image quality