Monitoring radiation exposure 2013 update standards tools and ihe rem
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Monitoring Radiation Exposure (2013 Update): Standards, Tools and IHE REM. Michael F. McNitt-Gray, PhD, DABR, FAAPM Professor, Department of Radiology, David Geffen School of Medicine at UCLA Kevin O’Donnell Toshiba Medical Research Institute Tessa Cook, MD, PhD

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Monitoring Radiation Exposure (2013 Update): Standards, Tools and IHE REM

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Monitoring radiation exposure 2013 update standards tools and ihe rem

Monitoring Radiation Exposure (2013 Update): Standards, Tools and IHE REM

Michael F. McNitt-Gray, PhD, DABR, FAAPMProfessor, Department of Radiology, David Geffen School of Medicine at UCLA

Kevin O’Donnell

Toshiba Medical Research Institute

Tessa Cook, MD, PhD

Assistant Professor, Department of Radiology, University of Pennsylvania

1


Disclosures

Disclosures

  • K.O. :

    • Employee, Toshiba Corporation  

  • M.M-G:

    • Institutional research agreement, Siemens AG

    • Recipient research support Siemens AG

    • Consultant, Flaherty SensabaughBonasso PLLC

    • Consultant, Fulbright and Jaworski, LLC

2


Learning objectives

Learning Objectives

  • 1) Learn about key radiation exposure metrics, such as CTDI, and how to interpret them.

  • 2) Learn about radiation exposure monitoring methods and tools.

  • 3) Capturing dose information with the DICOM Radiation Dose SR (RDSR) standard.

  • 4) Managing RDSR objects with the IHE Radiation Exposure Monitoring (REM) Profile.

  • 5) Integrating "CT dose screens" from legacy systems into RDSR.

3


Learning objectives1

Learning Objectives

  • 6) Pre-scan dose pop-ups on the CT console defined by the MITA Dose Check standard.

  • 7) Recent AAPM guidance on their use.

  • 8) Learn how to specify the above features when purchasing and integrating Radiology Systems.

  • 9) Learn about components of a dose management program such as protocol optimization.

  • 10) Participation in the ACR Dose Registry, and reporting requirements such as California SB-1237.

4


Outline

Outline

  • CT Dose Definitions and Uses – MMG

  • IHE REM, DICOM RDSR and Standards – KO

  • How to use dose information in practice - TC

5


Ct specific dose definitions

CT –Specific Dose Definitions

  • Computed Tomography Dose Index (CTDI) & its cousins

    • CTDI100

    • CTDIw- weighted

    • CTDIvol

    • Dose Length Product (DLP)

  • Dose Reports


Monitoring radiation exposure 2013 update standards tools and ihe rem

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)

7


Monitoring radiation exposure 2013 update standards tools and ihe rem

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)

8


Ctdi phantoms

CTDI Phantoms

  • Body (32 cm diam), Head (16 cm diam)

  • Holes in center and at 1 cm below surface


Ctdi defined

CTDI – defined

  • CTDI Does Represent:

    • Average dose in a phantom

    • along the z direction

    • at a givenpoint (x,y) in the scan plane

    • over thecentral scan of a series of scans

    • when the series consists of alarge number of scansseparated by the nominal beam width (contiguous scanning)


Ctdi 100

CTDI100

  • CTDI100 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

Some typical CTDI100 values

60 mGy

20

20

10

60

60

60

60

20

Head

Body


Ctdi w

CTDIw

  • CTDIw is a weighted average of center and peripheral CTDI100 to arrive at a single descriptor

  • CTDIw = (1/3)CTDI100,center + (2/3)CTDI100,peripheral


Ctdi vol

CTDI vol

  • Calculated, not measured directly

  • Based on CTDIw, but accounts for pitch

  • CTDIvol = CTDIw/ Pitch


Ctdi vol in context of aec

CTDIvol in Context of AEC

  • When Tube current modulation is used:

    • CTDIvol reported is based on the average mA used throughout the scan


Monitoring radiation exposure 2013 update standards tools and ihe rem

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


Dlp defined

DLP – defined

  • Dose Length Product is:

    • CTDIvol* length of scan (in mGy*cm)

  • Found in most “Dose Reports”

  • Includes any overscan (extra scanning for helical scans)


Takeaway ctdi vol dlp

Takeaway – CTDIvol, DLP

  • CTDIvol is reported on the scanner and in dose reports

  • CTDIvol is Dose to one of two phantoms

    • (16 or 32 cm diameter)

  • CTDIvol is a good descriptor of scanner output

    • Indicator of how output is adjusted for patient size

    • Larger patients SHOULD have a larger CTDIvol


Mita s xr 25 dose check alert

MITA’s XR-25 Dose Check – Alert

  • Alert Value: A value of CTDIvol or DLP used to trigger an alert when system projects that prescribed scans in an exam would result in a cumulative dose index value that exceeded this alert value.

  • An alert value is associated with a complete examination protocol, not with individual scans

  • The cumulative dose index value is compared to the alert value at each anatomic position throughout an examination.

  • Based on cumulative dose index value. So while any individual scan might not trigger a notification or alert, if the cumulative value at any anatomic position were expected to exceed the alert value when the next scan was performed, an alert would be triggered prior to scanning.

18


Mita s xr 25 dose check alert1

MITA’s XR-25 Dose Check – Alert

  • Notification is a Pop-up window PRIOR to scanning

  • User can verify settings are correct or change settings

  • To proceed with scanning following an alert, the operator is required to enter his or her name and either confirm or change the scan settings.

  • If a scan were performed that resulted in a cumulative dose index value that exceeded an alert value, the system would record the date and time, operator’s name, a unique study identifier, the associated alert value, actual cumulative dose index value, and any operator comment that might have been entered (e.g. “Very Large Patient, Multiple Phases”)

  • FDA has suggested an alert value for CTDIvol of 1000 mGy

19


Mita s xr 25 dose check notification

MITA’s XR-25 Dose Check - Notification

  • Notification Value: a Value of CTDIvolor DLP used to trigger a notification when value would likely be exceeded by prescribed scan

  • Notification is a Pop-up window PRIOR to scanning

  • User can verify settings are correct or change settings

  • NOTE: Each phase of a multi-phase examination is assessed independently of the other phases.

  • Different notification values can be set for each scan of an examination protocol.

20


Mita s xr 25 dose check configuration

MITA’s XR-25 Dose Check - Configuration

  • The FDA has suggested an alert value for CTDIvol of 1000 mGy,

  • AAPM suggested notification values

  • Can be changed at local site

21


Acr ct dose reference values

ACR CT Dose Reference Values

  • Based Solely on CTDIvol (not DLP)

  • Two levels:

    • Reference level and Pass/Fail level

  • ExamRef Level Pass/Fail Level

    • Adult Head*75 mGy80 mGy

    • Adult Abdomen*25 mGy30 mGy

    • Ped (5 y/o) Abd*20 mGy25 mGy

    • Ped(1 y/o) Head *45 mGyNone (yet)

    • All values pertain to a single phase, NOT cumulative from multi-phase exams

    • All assume a “standard sized patient”, larger patients can exceed these values

    • *Adult Head, pedsabd and peds head are based on 16 cm phantom


Aapm protocols

AAPM Protocols

  • For All Manufacturers

    • Already posted on AAPM public website

      • Adult Head Neuroperfusion

      • Adult Head

      • Adult Chest

      • Adult Abdomen

    • Not Meant to be “optimal”, but a good starting point

23


Monitoring radiation exposure 2013 update standards tools and ihe rem

24


Monitoring radiation exposure 2013 update standards tools and ihe rem

25


Limitations to ctdi

Limitations to CTDI

  • CTDIvol 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)


Aapm report 204

AAPM Report 204

Report also describes coefficients based on Lateral Width (from PA CT radiograph) and AP thickness (from Lat CT radiograph)


Ctdi vol and peak dose perfusion scans

CTDIvoland Peak Dose (Perfusion Scans)

  • CTDIvol 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


Ctdi vol and peak dose perfusion scans1

CTDIvoland Peak Dose (Perfusion Scans)

  • CTDIvol 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.


Ctdi vol1

CTDIvol

  • 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 CTDIvol 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”


Which phantom was used for ctdi

Which Phantom Was Used for CTDI

  • Currently:

  • ALL HEADS (Adult/Peds) – 16 cm phantom

  • ALL ADULT BODY – 32 cm phantom

  • 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)

      • CTDIvols differ by a factor of approx 2.5

      • This is changing towards all using 32 cm phantom, but still in transition (software upgrades, etc.)

  • PLEASE BE AWARE (this affects DLP, too)


California state law went into effect 7 1 12 important clauses

California State Law (went into effect 7-1-12)Important Clauses

  • 115111. (a) Commencing July 1, 2012….. shall record the dose of radiation on every diagnostic CT study produced during a CT examination in the patient's record….

  • (b) The facility conducting the study may send electronically 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

    • NOTE that CTs for radiation therapy planning or attenuation correct for Nuc Med are exempt

  • (d) the interpretive report of a diagnostic CT study shall include the dose of radiation by either recording the dose within the patient's report or attaching the protocol page that includes the dose of radiation to the report.

  • (f) For the purposes of this section, dose of radiation shall be defined as one of the following:

    • (1) CTDI volandDLP.

    • (2) The dose unit as recommended by the American Association of Physicists in Medicine.


To comply with state law

To Comply With State Law

  • Push All Dose Reports (Patient Protocol Pages/DICOM RDSR) to PACS

  • Include CTDIvol and DLP in “interpretive report”

  • Ok, but ummm….what do I do when….????


To comply with state law1

To Comply With State Law


To comply with state law faq

To Comply With State Law (FAQ)

  • Q: Some protocols require patients to have multiple CT scans. Are we required to record the dose index values in the PACS or radiology report for each scan, or can we record the highest values, average the values, or sum the values?

  • …..The facility has multiple options …for CT scans of the same body area.

  • If there are multiple sequences of the same body part, for example a three phase abdomen, you may report the values in a few different ways to meet the requirements:

    • eachCTDIvol and DLP value displayed may be reported;

    • the CTDIvol and the DLP may be summed and only the results reported; or

    • the highestCTDIvol and the DLP may be reported as well as the number of sequences performed to which the maximum values apply.

    • You may use one of these methods for CTDIvol and another for DLP.

  • If you perform scans for different areas of the body during a single examination, each area of the body needs the dose index values recorded separately if the CT system is capable of displaying the values separately.


Compliance with ca state law

Compliance with CA State Law

  • Some Univ. of CA campuses are manually dictating from Patient Protocol Page into Radiology Report

    • Manual, prone to errors (voice dictation systems don’t like numbers very much)


Compliance with ca state law1

Compliance with CA State Law

  • Informatics Solution

HL-7

token

Patient Protocol Page

Radimetric’seXposure server

Nuance

Powerscribe

Radiology report


Reporting dose a roadmap

Reporting Dose: A Roadmap

  • Phase 1a (Some of Us Are Currently Here):

    • Patient Protocol Page, Info. Manually Dictated into Radiology Report

  • Phase 1b (Some of Us are Currently Here):

    • DICOM SR, Still Manually Dictated into Radiology Report

    • Some scanners create DICOM SR, not easy to read and dictate

  • Phase 1c (Some of Us are Here …and just made it by July 1, 2012)

    • DICOM SR or Dose Report, 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, Summary of Organ Doses; Auto-Insert into Radiology Report

  • Phase 5: ????


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