CT Operator Check of Dose Indicator/Dose Indices

Rule 713. (2) The CT operator shall check the display panel before and after performing each scan to make sure the amount of radiation delivered is appropriate for the technique and individual patient. This may be accomplished by reviewing dose indicator devices if available or dose indices such as the technique factors. Dose indicators or indices outside of expected values shall be documented and reviewed by an interpreting physician or medical physicist.

Discussion:
This rule was based on a recommendation of the Food and Drug Administration (FDA). The FDA became aware of radiation overexposures during perfusion CT imaging to aid in the diagnosis and treatment of stroke (Safety Investigation of CT Brain Perfusion Scans: Initial Notification). Their investigation lead to this and other recommendations for CT facilities. See Safety Investigation of CT Brain Perfusion Scans: Update 11/9/2010 for updated recommendations. This rule applies to all CT procedures, not just brain perfusion scans. Checking the dose indices before and after the scan, and taking action if the values seem unreasonable, will help prevent accidental overexposures.

Before and after each scan the operator must check the display panel to determine if the appropriate amount of radiation was used for the scan. There is no requirement to document the operator's routine check of the display panel. Only doses that are thought to be outside of expected values need to be documented and reviewed by the medical physicist or interpreting physician. The procedure a facility will use for checking the display panel should be included in the facility's quality assurance manual and shared with the CT operators. Inspectors will review the procedure the facility uses to check the display panel and document doses outside of expected values. Documentation of doses outside of expected values will also be reviewed during an inspection.

Question 1: We have a super user that is the only person that has been trained to change protocols. We do not have a display that states the anticipated radiation dose, but because these protocols are not changed by the technologist will that meet this rule? Also at the end of the exam a dose page is sent to the Radiologist for him to review on every scan. So the actual amount of radiation is documented for every patient.

Question 2: When does the state consider doses to be "outside of expected values"? At what level do we need to document and review with the interpreting physician or medical physicist?

Question 1: We have a super user that is the only person that has been trained to change protocols. We do not have a display that states the anticipated radiation dose, but because these protocols are not changed by the technologist will that meet this rule? Also at the end of the exam a dose page is sent to the Radiologist for him to review on every scan. So the actual amount of radiation is documented for every patient.

If the actual dose is not indicated on the machine prior to or after the scan, the technologist must observe the technique factors or protocol before and after the scan. The technologist should know, based upon their experience, if the indicated technique/protocol is appropriate. If it does not look appropriate, they should note the occurrence and bring it to the attention of the physician or medical physicist. By rule 713(1), changing of the protocols can only be done after consultation with the medical physicist.

Question 2: When does the state consider doses to be "outside of expected values"? At what level do we need to document and review with the interpreting physician or medical physicist?

Subrule 713(2) does not specify a value at what point a dose would be outside of expected values. Determination of what the expected values should be for each protocol is left to the experience, knowledge, and professional judgment of both the interpreting physician and medical physicist. The technologist should know, based upon their experience and professional knowledge, if the indicated technique or protocol is appropriate or outside of the values established by the facility.

The American Association of Physicists in Medicine (AAPM) has recommended values as starting points to setting notification values. The document AAPM Recommendations Regarding Notification and Alert Values for CT Scanners: Guidelines for Use of the NEMA XR 25 Dose-Check Standard includes a table of CTDIvol values for some routine protocols which could be used as an upper bound to trigger notification of the interpreting physician or medical physicist. The document also provides a good discussion of special cases to consider where these "notification values" may not be appropriate. The AAPM document may provide a good starting point for establishing upper bounds for routine procedures. Facilities must also consider the case of excessively low values since these may result in poor image quality and repeated procedures. Limits based on patient size and lower end values should be considered and included in any notification table as appropriate.

February 6, 2012