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Dose Warning Pop-Up Boxes: What Works What Doesn’t Why Not?

Dose Warning Pop-Up Boxes: What Works What Doesn’t Why Not?. Rich Mather, PhD Mark Olszewski, PhD. Dose Warning Pop-Up Boxes. Purpose: To issue a pop-up warning box if dose (e.g., based on CTDI vol , DLP, or dose rate) exceeds a certain threshold

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Dose Warning Pop-Up Boxes: What Works What Doesn’t Why Not?

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  1. Dose Warning Pop-Up Boxes: What WorksWhat Doesn’tWhy Not? Rich Mather, PhD Mark Olszewski, PhD

  2. Dose Warning Pop-Up Boxes • Purpose: To issue a pop-up warning box if dose (e.g., based on CTDIvol, DLP, or dose rate) exceeds a certain threshold • Concept has been implemented with limited success • Wider adoption has been slowed by implementation challenges, physics issues, and user dissatisfaction

  3. Warning for Scans in a Single Location • One approach: To issue a pop-up warning box if CTDIvol exceeds a certain threshold for repeated axial scans at a single location (e.g., brain perfusion) • Implementation in this context, in conjunction with recommended protocols, has been accepted by users • However, the context is limited

  4. General Warning Implementation • Issue a pop-up warning box if dose exceeds a certain threshold • Designed to trigger if CTDIvol or DLP exceeded reference values laid out in ICRP 87 • User has option of adjusting parameters or confirming the technique to proceed • Implemented on small test sample of US sites • Turned off due to implementation challenges and user dissatisfaction

  5. General Warning Implementation Reference Value Warning Dose from technique selected by user Options for user to proceed

  6. Implementation Challenges • Unable to account for contiguous body regions in one scan • No way to handle chest, abdomen, pelvis scan with single value • Can only implement one reference level warning per protocol

  7. Implementation Challenges • Difficult to link reference value to a default protocol properly • Existing protocol copied and overridden by users with new parameters for new protocols • Not able to update reference value to reflect new region of interest

  8. Implementation Challenges • Reference values not established for entire studies, only for one main acquisition • e.g. not for preview image, bolus tracking, etc • Not able to account for inappropriate number of acquisitions

  9. Implementation Challenges • DLP is dependent on variability of scan length based on patient size and clinical task • CTDIvol based on maximum or average mA when tube current modulation is used?

  10. Implementation Challenges • What to do when reference values change • Update of installed base • Which values to use? • Different references based on locale • Country specific • Society specific • Site specific

  11. Physics Issues • Reference values exist for a limited number of applications • ACR and ICRP have limited number and don’t agree with each other • ICRP not well known in US • European values don’t necessarily work in US • No reference values for multiple phase studies

  12. Physics Issues • Reference values not upper limits • e.g. represent 75th percentile of surveyed use • Many patients don’t fit with assumptions used for reference doses (e.g. size, clinical indication) • Reference doses often based on outdated surveys of sites (new technology and applications not taken into account)

  13. Physics Issues • Large variety of patients and clinical tasks • No regulatory established limit on dose • Not appropriate for manufacturers to establish limits or reference values • Values should be set by the medical and physics community • ACR • AAPM • ICRP • ICRU

  14. Not successful with users • Due to limitations of reference values • Pop-ups triggered frequently • Triggered with big patients • With scans not “routine” • Users ignored warning • Warning became meaningless • Not “their” reference values

  15. MITA Involvement • Consistent implementation • All manufacturers • Manufacturers willing to write a MITA standard • Medical and physics community • Decide on reference levels • Upper limits on “reasonable” dose • Hard limit or confirmation • MITA can commit to implement on all forward production systems

  16. IEC Document for Comments • 60601-2-44DC • clause 203.107 Safety measures against excessive X-radiation • (g) Means shall be provided to allow users to optionally enter a reference CTDIvol, CTDIvol per second, and/or a DLP as part of each protocol. Additionally, the scanner shall be able to check the confirmed scan’s dose parameters against these reference values and display a warning on the operator’s control panel if they are exceeded. The operator shall be required to confirm this message before continuing. This checking capability shall be provided as an option for user implementation. • For cases where the total number of rotations is not pre-programmed, such as interventional procedures, the warning message shall not require a confirmation of the message prior to continuing.

  17. Conclusions • Need direction defined • Level to warn at (reference, upper limit, etc) • User defined level or standard • Hard limit or confirmation • Per protocol or for entire study • Pop-ups should be rare events • Collaborative effort • Between MITA and medical, physics, regulatory communities

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