Presentation on theme: "Michael F. McNitt-Gray, PhD, DABR, FAAPM Professor, Department of Radiology, David Geffen School of Medicine at UCLA Kevin O’Donnell Toshiba Medical Research."— Presentation transcript:
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 Assistant Professor, Department of Radiology, University of Pennsylvania 1
Disclosures K.O. : Employee, Toshiba Corporation M.M-G: Institutional research agreement, Siemens AG Recipient research support Siemens AG Consultant, Flaherty Sensabaugh Bonasso PLLC Consultant, Fulbright and Jaworski, LLC 2
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 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
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 Computed Tomography Dose Index (CTDI) & its cousins CTDI 100 CTDI w - weighted CTDI vol Dose Length Product (DLP) Dose Reports
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
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 Body (32 cm diam), Head (16 cm diam) Holes in center and at 1 cm below surface
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)
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 Body 60 mGy 60 Head Some typical CTDI 100 values
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
CTDI vol Calculated, not measured directly Based on CTDI w, but accounts for pitch CTDI vol = CTDI w / Pitch
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
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 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)
Takeaway – CTDI vol, 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 Indicator of how output is adjusted for patient size Larger patients SHOULD have a larger CTDI vol
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 – 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 Notification Value: a Value of CTDI vol or 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 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 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 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, peds abd and peds head are based on 16 cm phantom
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
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)
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) 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 Jan-Feb;28(1):245-53
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.
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”
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 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 ) Important Clauses (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 vol andDLP. (2) The dose unit as recommended by the American Association of Physicists in Medicine.
To Comply With State Law Push All Dose Reports (Patient Protocol Pages/DICOM RDSR) to PACS Include CTDI vol and DLP in “interpretive report” Ok, but ummm….what do I do when….????
To Comply With State Law
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: each CTDIvol and DLP value displayed may be reported; the CTDIvol and the DLP may be summed and only the results reported; or the highest CTDIvol 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 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 Law Informatics Solution Patient Protocol Page Radimetric’s eXposure server Nuance Powerscribe HL-7 token Radiology report
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: ????