Kevin ODonnell Toshiba Medical Research Institute Michael F.
McNitt-Gray, PhD, DABR, FAAPM Professor, Department of Radiology
Director, Biomedical Physics Graduate Program David Geffen School
of Medicine at UCLA 1
Slide 2
Disclosures K.O. : Employee, Toshiba Corporation M.M-G:
Institutional research agreement, Siemens AG Recipient research
support Siemens AG Instructor, Medical Technology Management
Institute. 2
Slide 3
Learning Objectives 1) Understand integration challenges
involved in Monitoring Radiation Exposure. 2) Learn about capturing
dose information with the DICOM Radiation Dose SR (RDSR) standard.
3) Learn about managing RDSR objects with the IHE Radiation
Exposure Monitoring (REM) Profile. 4) Learn how data such as "CT
dose screens" from legacy systems can be ported into RDSR. 5) Learn
about pre-scan dose pop-ups on the CT console defined by the MITA
Dose Check standard and recent AAPM guidance on their use. 6) Learn
how to specify the above features when purchasing and integrating
Radiology Systems. 7) Learn about components of a dose management
program such as protocol optimization, dose QA programs and
participation in the ACR Dose Registry. 3
Slide 4
Outline CT Dose Definitions MMG IHE REM, DICOM RDSR and
Standards KO How to use dose information in practice - MMG 4
Slide 5
CT Specific Dose Definitions Computed Tomography Dose Index
(CTDI) & its cousins CTDI 100 CTDI w - weighted CTDI vol Dose
Length Product (DLP) Dose Reports
Slide 6
CTDI CTDI is an Index CTDI is dose in a phantom CTDI has LOTs
of good uses: It is a good measure of scanner output It is a good
index when comparing protocols and technical parameter settings It
is a very good indicator of how scanner output is being adjusted
with patient size (think peds protocols) 6
Slide 7
CTDI But CTDI has some limitations (we said it was an index)
Ex: CTDI is not a direct measure of patient dose (more on that
later) 7
Slide 8
CTDI Phantoms Body (32 cm diam), Head (16 cm diam) Holes in
center and at 1 cm below surface
Slide 9
CTDI defined CTDI Does Represent: Average dose in a phantom
along the z direction at a given point (x,y) in the scan plane over
the central scan of a series of scans when the series consists of a
large number of scans separated by the nominal beam width
(contiguous scanning)
Slide 10
CTDI 100 CTDI 100 Measurements are done: In Both Head and Body
Phantoms with 100 mm ion chamber At isocenter and at least one
peripheral position in each phantom 20 mGy 10 20 Body 60 mGy 60
Head Some typical CTDI 100 values
Slide 11
CTDI w CTDI w is a weighted average of center and peripheral
CTDI 100 to arrive at a single descriptor CTDI w = (1/3)CTDI
100,center + (2/3)CTDI 100,peripheral
Slide 12
CTDI vol Calculated, not measured directly Based on CTDI w, but
accounts for pitch CTDI vol = CTDI w / Pitch
Slide 13
CTDI vol in Context of AEC When Tube current modulation is
used: CTDI vol reported is based on the average mA used throughout
the scan
Slide 14
Scan where Tube Current Modulation was used Blue Curve
Represents actual instantaneous mA Red Curve Represents avg mA for
each image Yellow Curve Represents avg mA over entire scan Overall
avg is used for CTDIvol reported in Dose Report
Slide 15
DLP defined Dose Length Product is: CTDI vol * length of scan
(in mGy*cm) Found in most Dose Reports Includes any overscan (extra
scanning for helical scans)
Slide 16
CTDI vol and DLP CTDI vol is reported on the scanner and in
dose reports CTDI vol is Dose to one of two phantoms (16 or 32 cm
diameter) CTDI vol is a good descriptor of scanner output And can
be a good indicator of how output is adjusted for patient size
Think peds protocols here. Larger patients SHOULD have a larger
CTDI vol
Slide 17
Standards & Tools 17
Slide 18
Headers & Screen Shots Useful but limited Missing details
Not machine-readable Duplication issue Size issue 18
22 Other Details in Dose SR Full Patient / Order / Study
Details Unique ID for each Irradiation Event Equipment ID, Ordering
Doc, Performing Tech Patient Size, Orientation, Anatomy Imaged
Imaging Geometry X-Ray Filtering & Collimation Details Anode
Target Material Calibration, Phantom, Dosimeter, Patient Model
Slide 23
23
Slide 24
IHE REM Profile 24 Radiation Exposure Monitoring some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 Numer 12.2 14.5 9.5
10.9
Slide 25
25 IHE in One Slide IHE helps vendors implement & test
functions that span multiple systems Profiles are implementation
guides how to use existing standards to address a specific problem
scenario Connectathons are test events managed testing of Profile
implementations IHE helps users purchase & integrate
multi-system solutions list required IHE Profile support in
RFPs
Slide 26
26 IHE Radiation Exposure Monitoring Profile some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 National Registry
Archive Dose Information Reporter some text: # Numerical Details
12.2 14.5 11.8 7.6 Outlier: # Performing Phys. Over Target: 12.2%
some text: # Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some
text: # Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 some text: #
Numerical Details 12.2 14.5 11.8 7.6 9.5 10.9 Numer 12.2 14.5 9.5
10.9
Slide 27
27 Using SR Dose Reports Radiation QA Periodically Query /
Retrieve Reports from Archive Set policies/standards and flag
deviations Set goals for improvement and track progress Implement
protocol changes and compare difference in dose Patient Impact
Evaluation e.g. if Patient identified as pregnant post-facto Dose
Mapping Store data in realtime from Modality to Mapping
Workstation
Slide 28
28 Using SR Dose Reports National Registries Anonymize and
submit Dose Reports to Registry Compile Population Risk Estimations
Derive Dose Reference Levels (DRLs) Provide Site-Site Comparisons
Individual Dose Record Collect Dose Reports over time Clinical
Trials Collect Dose together with Images Demonstrate both improved
detection & reduced dose
Legacy Extractor What if you cant get REM? Extractors create
(partial) REM objects Based on OCR of dose screens Based on image
header contents Based on MPPS Likely incomplete but still useful
Allows use of uniform infrastructure (RDSR) Current focus: CT, some
XA
Slide 31
Example Extractors Open Source Dose Utility - dclunie.com by
David Clunie (PixelMed) Radiance - radiancedose.com by Tessa Cook
(Hospital of U of Pennsylvania) GROK dose-grok.sourceforge.net by
Graham Warden (Brigham and Women's Hospital) Also Valkyrie
(considering open source) by George Shih (Weill-Cornell) ACR Triad
Site Server (included in ACR participation) by Mythreyi Chatfield
(ACR)
Slide 32
ACR DIR 32 Dose Index Registry
Slide 33
ACR Dose Index Registry nrdr.acr.org Open to facilities
worldwide Anonymized data submission (via IHE REM or legacy
extractor) Provides periodic reports Dose statistics Site
Comparisons Modest annual participation fee 33
Slide 34
ACR Activity Tracking practice Understand current dose patterns
Provide basis for establishing DRLs Not tracking
patient/longitudinal Procedure Naming Issue Comparison requires
consistent naming Local consistency vs National consistency ACR
maps to Radlex Playbook 34
MITA CT Dose Check Initiative Goals Enhance dose awareness
(CTDI/DLP) Help to avoid excessive radiation events Provide data to
sites for QA MITA has published the standard (XR-25)* Manufacturers
worked to ensure Uniformity Speed of implementation Breadth of
deployment *Available at: http://www.nema.org/stds/xr25.cfm
Slide 37
Dose Notification Pop-up message Notifies technologist that
dose for the current scan element will exceed a trigger value Tech
may: confirm and proceed, or go back and adjust scan parameters
System records audit trail Predicted dose, Notification value,
Date/time, diagnostic reason, etc. Clinical sites set values that
will trigger a notification Can set DLP and/or CTDI vol values for
each scan element e.g. head without contrast Defined by the
clinical site for their patient population
Slide 38
Dose Alert Pop-up message Alerts technologist cumulative dose
for current study will exceed a trigger value: CTDI vol (summed at
each patient location) DLP (summed over the current study) Tech
may: enter their name, (& a password if configured), confirm
and proceed, or go back and adjust scan parameters Clinical sites
set values that will trigger an alert Can set DLP and/or CTDI vol
values System must allow at least one global value System tracks
accumulated CTDI vol at each patient location & accumulated DLP
System checks predicted accumulated dose indices when protocols are
saved & when scans are ready
Slide 39
Default Values The FDA has suggested an alert value for CTDIvol
of 1000 mGy, AAPM suggested notification values Can be changed at
local site 39
Slide 40
Audit Trails Pop-up Overridden? System must record: Dose
Notification Predicted dose, Notification value, Date/time,
Diagnostic reason Dose Alert Predicted dose, Alert value,
Date/time, Diagnostic reason, Operator name RDSR has fields to
record all these details May choose to record even if not
overridden Triggers vs DRLs 75 th percentile -> popups on 25% of
scans See AAPM guidance
Slide 41
Implementation Progress IHE REM Testing: IHE Connectathon
http://connectathon-results.ihe.net Product: IHE Integration
Statement http://product-registry.ihe.net DICOM RDSR Product: DICOM
Conformance Statement NEMA XR-25 Vendors commitment; some products
already released 41
Slide 42
Takeaway Data Collection New/recent Modalities IHE REM / DICOM
RDSR to capture dose data Legacy strategies Dose extractors to
generate RDSR data Analysis IHE REM Dose Information Reporter for
local analysis ACR Dose Registry to compare to benchmarks
Prevention CT Dose Check for configurable pre-scan alerts
Slide 43
Things to Implement in Practice Turn On/Upgrade to get these
Informatics Tools Make sure CTDIvol is displayed on all of your CT
scanners Can be turned off, so make sure Make sure Patient Protocol
pages are sent to PACS Not always automatically sent to PACS, so
make sure RDSR (may require software upgrade, so check) MITAs Dose
Check (also may require software upgrade) Consider joining ACRs
Dose Index Registry 43
Slide 44
Things to Implement in Practice Review CT protocols All if
possible, but at least top 10 highest dose and/or usage One key
question Fewer Protocols? Or More Protocols?: Build a basic
protocol that is inclusive and ask techs to adapt (in real time) at
scanner Build protocols for each possible situation and have them
listed separately on the scanner (e.g. peds 16kg) Some combination
of these two 44
Slide 45
Things to Implement in Practice What to review Review
Indications and Requirements for Exam What do you need to see? What
amount of noise can you tolerate? Technical parameters (kVp, mAs,
pitch, etc.) Examine CTDIvol and DLP values for protocols Determine
number of phases necessary for indication Are both pre- and
post-contrast necessary on all patients? Are different enhancement
phases necessary (arterial/venous)? 45
Slide 46
ACR CT Dose Reference Values Based Solely on CTDI vol (not DLP)
Two levels: Reference level and Pass/Fail level Exam Ref Level
Pass/Fail Level Adult Head*75 mGy80 mGy Adult Abdomen*25 mGy30 mGy
Pediatric (5 y/o) Abd*20 mGy25 mGy Pediatric Head*45 mGyNone (yet)
All values pertain to a single phase, NOT cumulative from
multi-phase exams Adult Head, peds abd and peds head are based on
16 cm phantom
Slide 47
AAPM Protocols For All Manufacturers Brain Perfusion already
posted on AAPM public website Coming Soon Routine Head Routine
Chest Routine Abdomen Routine Cardiac Not Meant to be optimal, but
a good starting point 47
Slide 48
Things to Implement in Practice Review Usage Ex.: Summary
Statistics from ACR Dose Index Registry Use tools to help identify
high dose exams and outliers Understand reasons for high dose
values Large Patient (for Body exams) Multiple Phases Ensure
Compliance with Protocols 48
Slide 49
Things to Implement in Practice Reporting Dose in Patient
Record and Radiology Reports? Why are you going to do this?
Required by State Law (e.g. CA)? Its the right thing to do? 49
Slide 50
Limitations of CTDI vol Some things you should know before you
start reporting dose in patient records CTDI vol is Dose to one of
two phantoms (16 or 32 cm diameter) CTDI vol is a good descriptor
of scanner output And can be a good indicator of how output is
adjusted for patient size Think peds protocols here. Larger
patients SHOULD have a larger CTDI vol 50
Slide 51
Limitations of CTDI vol CTDI is not a direct measure of patient
dose See McCollough et al, Radiology. 2011 May;259(2):311-6. PMCID:
PMC3079120 Need other information (such as patient size) to provide
accurate estimate of individual patient dose
Slide 52
CTDI vol and Patient Size For most body exams, it is proper to
adjust scanner output for patient size Larger output for larger
patients Lower output for smaller patients Larger patients will
typically have a larger CTDI vol This is not a bad thing, it
reflects proper adjustments in tube output 52
Slide 53
Scenario 1: No adjustment for patient size 32 cm phantom CTDI
vol = 20 mGy The CTDI vol (dose to phantom) for these two would be
the same 100 mAs
Slide 54
Scenario 2: Adjustment for patient size 32 cm phantom CTDI vol
= 10 mGy CTDI vol = 20 mGy The CTDI vol (dose to phantom) indicates
larger patient received 2X dose 50 mAs 100 mAs
Slide 55
Did Patient Dose Really Increase ? For same technical factors,
smaller patient absorbs more dose Scenario 1: CTDI is same but
smaller patients dose is higher Scenario 2: CTDI is smaller for
smaller patient, but patient dose is closer to equal for both
Slide 56
Limitations to CTDI CTDI vol does not account for patient size
Even though you may see different values for patients of different
size; this is because scanner output is being (usually properly)
adjusted for patient size AAPM Report 204 describes a method to
take into account patient size The Size Specific Dose Estimate
(SSDE)
Slide 57
AAPM Report 204 Report also describes coefficients based on
Lateral Width (from PA CT radiograph) and AP thickness (from Lat CT
radiograph)
Slide 58
CTDI vol and Peak Dose (Perfusion Scans) CTDI vol is a weighted
average of measurements made at periphery and center of cylindrical
phantom Defined to reflect dose from a series of scans performed
w/table movement From Bauhs et al, Radiographics. 2008
Jan-Feb;28(1):245-53
Slide 59
CTDI vol and Peak Dose (Perfusion Scans) CTDI vol is a weighted
average of measurements made at periphery and center of cylindrical
phantom Defined to reflect dose from a series of scans performed
w/table movement Is not patient dose (not even skin dose) Typically
OVERestimates skin dose in cases where scan is performed with no
table movement (e.g. perfusion scans) See article by Zhang et al,
AJR Feb 2012 (in press).
Slide 60
CTDI vol and DLP Need other information such as patient size,
body region, clinical indication to determine if scan was done
correctly or Alara
Slide 61
CTDI vol Not patient dose and by itself can be misleading
Should be recorded with: Description of phantom size (clarify 16 or
32 cm diameter) Description of patient size (Lat. Width, Water Eq.
Diam) Description of anatomic region If CTDI vol is recorded
without any patient size information, then some disclaimer could be
added: The dose values reported here are an estimate and represent
dose to a standard phantom; they do not take into account patient
factors such as patient size
Slide 62
Still want/need to Report Dose? Lets look at what is available
to report 62
Slide 63
Which Phantom Was Used for CTDI Currently: ALL HEADS
(Adult/Peds) 16 cm phantom ALL ADULT BODY 32 cm phantom PEDS BODY
(CAUTION!!!!): PEDS BODY (CAUTION!!!!): Siemens, Philips: report
based on 32 cm phantom Toshiba and GE**: report 16 OR 32 cm
(depends on SFOV or patient size) CTDI vol s differ by a factor of
approx 2.5 So, previous example, CTDI vol,32 = 1.71 mGy If report
used 16 cm phantom, CTDI vol,16 ~ 4.1 mGy PLEASE BE AWARE (this
affects DLP, too)
Slide 64
California State Law ( SB 1237) Important Clauses 115111. (a)
Commencing July 1, 2012.. (b) The facility conducting the study
shall electronically send each CT study and protocol page that
lists the technical factors and dose of radiation to the electronic
picture archiving and communications system. Patient Protocol page
or DICOM RDSR fulfills this requirement (d) Subject to subdivision
(e), the radiology report of a CT study shall include the dose of
radiation by either recording the dose within the patients
radiology report or attaching the protocol page that includes the
dose of radiation to the radiology report. Not all scanners are
capable of CT RDSR Would be nice to electronically integrate with
radiology report (f) For the purposes of this section, dose of
radiation shall be defined as one of the following: (1) The
computed tomography index volume (CTDI vol) and dose length product
(DLP), as defined by the International Electrotechnical Commission
(IEC) and recognized by the federal Food and Drug Administration
(FDA). (2) The dose unit as recommended by the American Association
of Physicists in Medicine.
Slide 65
To Comply With State Law We only need to report CTDI and DLPs
But which ones? Individual CTDI/DLPs? Totals? Both?
Slide 66
When Does It Make Sense to Add CTDI vol s When same anatomic
region is scanned repeatedly and assumptions of CTDI apply (table
movement, large anatomic region such as head, chest, abdomen, etc.)
Examples: Non-con chest followed by post-contrast chest
Slide 67
When Does It NOT Make Sense to Add CTDI vol s Different
anatomic regions No table motion (perfusion scan)** Examples: chest
followed by abdomen/pelvis ** CTDIvol OVER estimates Peak Dose
(e.g. Skin or Eye Lens in Neuroperfusion scans) Adding these
CTDIvols may be the best we can currently do, but the sum ONLY
Pertains to limited area of perfusion scan
Slide 68
When Does It Make Sense to Add DLPs Similar to CTDIvols When
same anatomic region is scanned repeatedly and assumptions of CTDI
apply (table movement, large anatomic region such as head, chest,
abdomen, etc.) Examples: Non-con chest followed by post-contrast
chest
Slide 69
When Does It NOT Make Sense to Add DLPs Again, Similar to
CTDIvols Different anatomic regions No table motion (perfusion
scan) Examples: Head followed by C/A/P Even Chest followed by
abdomen/pelvis
Slide 70
Reporting Dose: How To Do It Right? Phase 0 (We Are Currently
Here): Patient Protocol Page, Info. Manually Dictated into
Radiology Report Phase 1 (We are Part of the Way Here): DICOM SR,
Still Manually Dictated into Radiology Report Some scanners create
DICOM SR, not easy to read and dictate Phase 2 (We WANT to be Here
before July 1, 2012) DICOM SR, Auto-insert into Radiology Report
Phase 3: DICOM SR, Body Region and Size Adjusted, Auto-insert into
Radiology Report Phase 4: DICOM SR, Body Size Adjusted, Organ
Doses; Auto-Insert into Radiology Report Phase 5: ????
Slide 71
A Final Word - Effective Dose Effective Dose is a concept
borrowed from health physics (people who work in radiation industry
including nuclear power plants, radiologists, rad. Techs, med.
Physicists). Effective Dose was never intended for dose to an
individual; intended for populations
Slide 72
Effective Dose E = T (w T *D T,R ) w T = tissue weighting
factor (next page) D T,R = average absorbed dose to tissue T Units
are: SI - Sieverts (Sv); English -rem 1 rem = 10 mSv; 1 Sv = 100
rem Looks simple, doesnt it?
Slide 73
Effective Dose Tissue ICRP 60 Tissue weightsICRP 103 tissue
weights Gonads (avg male/female)0.200.08 Red Bone Marrow 0.120.12
Colon (wall, not contents)0.120.12 Lung0.120.12 Stomach (wall, not
contents)0.120.12 Bladder (wall, not contents)0.050.04 Breast
(glandular)0.050.12 Liver0.050.04 Esophagus0.050.04 Thyroid0.050.04
Skin0.010.01 Bone Surface0.010.01 Brain(part of remainder)0.01
Remainder0.050.12
Slide 74
One approximation: E= DLP * k, where E = Effective Dose in mSv
DLP = Dose Length Product in mGy*cm k = conversion coefficient in
mSv/mGy*cm k =.0021 mSv/mGy*cm for adult head k =.014 mSv/mGy*cm
for adult chest k =.015 mSv/mGy*cm for adult abdomen/trunk DLP*k
Method to Estimate Effective Dose
Slide 75
Formula is based on approximation of a curve fit for several
scanners (circa 1990) between E and DLP based on Monte Carlo
simulations Patient model was standard man size 20-30 year old
MALE, 70 kg, 57 tall With both male and female organs k values are
based on ICRP 60 organ weights
Slide 76
Effective Dose Again, effective Dose was never intended for
dose to an individual; intended for populations Simple method
(DLP*k) has several limitations Does not adjust for patient size
Not designed for Tube Current Modulation methods
Slide 77
Summary (1) Dose Metrics CTDI vol is reported on the scanner
and in dose reports CTDI vol is Dose to one of two phantoms (16 or
32 cm diameter) CTDI vol is a good descriptor of scanner output And
can be a good indicator of how output is adjusted for patient size
(e.g. peds protocols). Larger patients SHOULD have a larger CTDI
vol
Slide 78
Summary (2) Reporting Tools Data Collection New/recent
Modalities IHE REM / DICOM RDSR to capture dose data Legacy
strategies Dose extractors to generate RDSR data Analysis IHE REM
Dose Information Reporter for local analysis ACR Dose Registry to
compare to benchmarks Prevention CT Dose Check for configurable
pre-scan alerts 78
Slide 79
Summary (3) Implementation Hints Turn On/Upgrade to get these
Informatics Tools Review CT protocols Review Technical parameters,
CTDIvol and DLP values Determine number of phases necessary for
indication Review ACR CT Accreditation Program Guidelines Review
AAPM protocols Review Usage ACR Dose Index Registry Use tools to
help identify high dose exams and outliers
Slide 80
Summary (4) Reporting Patient Dose CTDI vol Is not patient dose
Is not skin dose overestimates skin dose for perfusion scans Is
dose to a reference sized phantom Reference can vary from Peds to
Adult or it might be same Will vary with patient size.and that is
ok. Needs to be adjusted for patient size (SSDE) Need methods to
determine when to add CTDIs and when not to (especially in
automated fashion)