The Challenge of CT Dose Records

Transcription

1 The Challenge of CT Dose Records Kimberly Applegate, MD, MS, FACR Professor of Radiology and Pediatrics Emory University *financial disclosures: -Springer Textbook contracts -AIM advisory board for patient radiation safety

2 Aims Background Principles Advantages / Disadvantages of CT Dose Records What should we record? How to capture dose? What about other modalities? Access and Privacy Conclusions and Discussion

3 Background: Radiation Protection 3 Key Principles 1. Justification 2. Optimization 3. Dose Limits* *in medicine, use of Diagnostic Reference Levels and Audits

4 Background International BSS 1996 (rev 2011) No dose limits but DRLs Revision: Include dose estimates in reports Growing pressures by regulators, payors, public to do something to protect the public Cancer risk: repeat CTs dose estimate> 100 msv Deterministic risks: CT perfusion for stroke California State Law: Oct 2010

5 Background Potential Advantages: a. Indirectly stimulate dose reduction policies, practices, audits, guidelines, standardization b. Contribute to epidemiological research c. Potentially standardize dose metrics d. Track pts with high exposures, educate consumers Potential Disadvantages: a. Confuse/scare consumers with data they do not understand b. Are dose estimates meaningful at current state of science?

6 Recording Mechanism how do we record? Logbook (eg, IR) Scan into PACS Record in eemr, each event, not additive Cumulative record in eemr EPIC

7 What should we record? Number of CT examinations? Descriptive protocol record? Technical parameters? Numerical dose metric CTDI vol / DLP? Convert to Effective Dose?

8 Number of CT examinations + basic descriptive protocol CT Head with and without contrast CT Abdomen and Pelvis, one phase Simple Data entry easy Broad impression info to referring physicians 2 or 20 previous CT? Acknowledgment of record likely to contribute towards a culture of increased radiation safety awareness Avoids potential undue fixation on complex numerical dose parameters

9 however No dose data for patient referring physician radiologist physicist regulatory bodies prospective / retrospective studies Promotes misperception all CT examinations are about the same dose Risks inappropriate alarm or reassurance by mere numerical count

10 Range of Pediatric CT Effective Dose CT Effective Dose Estimates for a 5-10 yr old child, 2010 Hospital for Sick Children, Toronto 10 Abdo/pelvis CT = 10 HRCT Risk -? avoidance of (low dose) CTs need dose info 50 X dose msv Estimates based on 5-10 yr old patients, using weightadjusted protocols (GE 750 HD) and DLP:ED conversion coefficients (Shrimpton et al., NRPB-W )

11 Technical parameters? mas / kvp used in past as broad indicator of dose Advances in MDCT technology - no longer adequate If aim is to enable a physicist to estimate organ or effective dose will require many data fields incl. detector configuration, beam width, kvp, ma / effective mas/ ATCM parameters/design, pitch/table speed, scan length.. Practicable? depends on recording method Would info be useful? Would it be used? Meaningful to those viewing the record?

12 Numerical dose metrics CTDI vol + DLP? Standardized dose metrics CTDI vol = (1/3 CTDI 100.c + 2/3 CTDI 100.p ) / pitch DLP = CTDI vol x scan length In use currently All vendors have capability for console display Export of dose page to PACS relatively easy

13 Be aware - 1. CTDI vol and DLP do NOT measure PATIENT dose Indication of radiation INCIDENT on the patient Measured using two standardized polymethylacrylate cylindrical phantoms 16 cm diameter (head or pediatric body) 32 cm diameter (adult body) CTDI vol = (1/3 CTDI 100.c + 2/3 CTDI 100.p ) / pitch DLP = CTDI vol x scan length 32 cm phantom 16 cm phantom

14 Head CT Body CT 2. Variable use of 16 and 32 cm phantoms in Pediatric Body CT Dosimetry All ages 16 cm phantom Adult - 32 cm phantom Pediatric - variable use of 16 and 32 cm phantoms Variability Vendors Research groups / literature Diagnostic Reference Level CT Dose Surveys The CTDI or DLP recorded using a 16 cm phantom will be approximately double that recorded using a 32 cm phantom for the same scan parameters CTDI vol (16) = 2 x CTDI vol (32) DLP (16) = 2 x DLP (32) XX X

15 We must Know which phantom is being used for every ped body scan (vendor, protocol selected, FOV) Have clear vendor display of phantom size Know how to convert for equivalency between 16 cm and 32 cmbased pediatric body dose data (X 2 X ½) Record phantom size in CT dose record Aim for consistency between vendors CTDI vol / DLP Standardized parameters Display easily achieved Transferable to PACS / other systems Allow comparison between institutions/ protocol approaches / correlation with and participation in CT (DRL) Dose Surveys Best available / most practicable?

16 Convert to Effective Dose? the sum of the absorbed doses in all tissues and organs in the radiation field, each multiplied by a tissue-specific weighting factor Useful To assess the relative dose impact of radiographic, fluoroscopic, CT and NM examinations to the exposed population To compare with annual background radiation To provide a broad estimate of future excess malignancy risk when used with risk models

17 However Not intended for individual dose and risk assessment Intrinsic assumptions, extrapolations and changing weighting factors Numerous methodologies Incl. software, direct dosimetry, conversion factors, others Conversion factors? 30 % variability in result DLP msv or 1.7 msv or 2.3 msv? Several pediatric versions available / may be updated Need to convert 32 cm body data for use with 16 cm CF often not appreciated - error X 2 When does a child become an adult? 13? 15? Effective dose is not a reproducible measurement it is an estimate Use Caution Must include source data (CTDI vol /DLP) and method

18 How to Capture Dose? RADIANCE: UPenn Open source software extracts DICOM SR to eemr Valkyrie: Weill/Columbia (GE) software burns (effective) dose onto image, adjusts for pt position, size, age, gender SMARTCARD: IAEA.org Records dose protocol onto credit card for lifetime record

19 More Products PENMET: skindoses /arrtasrtco aspx/ Output ready to HIS DoseMonitor: Cumulative dose; all modalities Customizable alerts

20 Dose Capture Products EPIC RADIANT (RIS) since 2009 Customizable calculation; multivendor Most use msv ; dose accumulator app Pulls DICOM dose metric Displays on RIS, not eemr until 2011 release SerphyDose:web.lerelaisinternet.com/serphydose GE purchase (DoseWatch), multivendor app Dose calculation (msv) from tech parameters Separate from RIS, eemr Pilots underway at 4 sites in USA

21 Multimodality Dose Records? CT = largest contributor to population exposure demand to establish dose records Consider effective dose from individual examinations - other modality examinations of similar/ higher dose - nuclear medicine, interventional (therapeutic) procedures

22 Effective Dose Estimate (msv) Effective Dose Estimates for a 5 year old child Institutional data, Hospital for Sick Children, Toronto

23 Multimodality Records? CT record vs multimodality record? CT record first Be aware of potential message/ misperception CT doses are higher than other examinations only need to worry about CT Alter imaging referral patterns inappropriately?

24 Access and Privacy: Who, What, and Where Who should have access? Radiology, Payor, HC System, Patient What should be recorded? Utilization, Dose, Imaging Parameters Where do we keep the records? PACS, RIS, EMR, registry, web portal

25 Access and Privacy: Example BI-DEACONESS: Patient portal PatientSite Free access, login; notifications No access to cancer or HIV lab results Delay for imaging reports: 4 days after signed No current dose record Need for national web registry for health records? Patient access or control?

26 Discussion: Registries American College of Radiology National Dose Index Registry: allows facilities to compare their CT dose indices to regional and national values Open to international CT users Current: 300+ users

27 Conclusion/Discussion Many potential advantages of CT dose record in patient EMR Lack of agreement on single meaningful metric Which approach(s) will be most beneficial / effective? Need for continued collaboration to best solve complex issues - IT engineering - medical societies - medical physicists - consumers - regulatory agencies

28 Questions?

29 Effective Dose Estimate (msv) Effective Dose Estimates for a 5 year old child Institutional data, Hospital for Sick Children,

30 Effective Dose Estimate (msv) Effective Dose Estimates for a 5 year old child Institutional data, Hospital for Sick Children,

31 Effective Dose Estimate (msv) Effective Dose Estimates for a 5 year old child Institutional data, Hospital for Sick Children,