Posted on 1 Comment

CTDIvol vs DLP – a simple explanation

What do they represent? CTDIvol is based on measurements obtained when scanning either a 16cm or 32 cm phantom.   Essentially, it represents scanner output.  DLP is derived from CTDIvol, but incorporates a scan length component.  Both function as reasonable proxies for absorbed dose but do not represent the actual patient dose.  In other words, if your CTDIvol and/or DLP is twice as high as it could be, then the doses you are imparting will be about twice as high as they could be.

Can CTDIvol and DLP results tell me two different things?     Yes.  CTDIvol represents the output when scanning a phantom, while DLP takes into account the scan length.  We’ve seen instances where CTIDvol is considered well within a “normal” range but DLP was unexpectedly high.  We found the scan settings were appropriate for the study, but the exam length  was longer than what others were using.

For example, a Chest CT could be started too high into the neck and end too far into the abdomen.  If this is the case CTDIvol (basic scanner settings) could be just fine, but because scans extended more than necessary above and/or below the requested area, the DLP could easily be too high.

—————————————————

The following information, obtained from RadDaily.com, is a more technical discussion of CTDIvol and DLP for those interested.

The following is taken from an article posted on RadDaily.com

CT Dose Index Volume (CTDIvol) The CTDIvol can be calculated as: CTDIvol = [(N x T)/I] x CTDIw where CTDIw = weighted or average CTDI given across the field of view N = number of simultaneous axial scans er x-ray source rotation T = thickness of one axial scan (mm) I = table increment per axial scan (mm)

In helical CT the ratio of the I to (N x T) is the pitch; therefore in helical mode:  CTDIvol = (1/pitch) x CTDIw

CTDIvol (or CTDI volume) represents the dose for a specific scan protocol which takes into account gaps and overlaps between the radiation dose profile from consecutive rotations of the x-ray source. Therefore CTDIw represents the average radiation dose over the x and y direction whereas CTDIvol represents the average radiation dose over the x, y and z directions.

Dose Length Product The dose length product (DLP) is the measure of ionizing radiation exposure during the entire acquisition of images.

Therefore, DLP (mGy-cm) = CTDIvol (mGy) x irradiated length (cm) (irradiated length is usually longer than imaged length in helical scanning)

CTDIw and CTDIvol are independent of scan length for determining the total energy absorbed whereas DLP is proportional to scan length.


Need help getting more from your participation in the ACR’s Dose Index Registry® ?  Let Dose Registry Support Services tailor a program designed specifically to help your department succeed.  Contact Dose Registry Support Services to see how we can help.

Posted on Leave a comment

DoseID helps facilities identify duplicate and superfluous scanner protocols

One of the more interesting and unique benefits Dose Registry Support Services’ DoseID Program has for facilities is its ability to shed light on duplicate and superfluous protocols in use at their facilities.  DuplicatedProtocols

The table to the right shows how one facility had 7 different protocols being used on a single scanner during a recent 3 month period.  As you can see, all protocols are purportedly for a CT Abdomen/Pelvis without contrast exam, yet they are used with significantly varying frequency.  One is used by staff 714 (79%) of the 903 without contrast studies performed, yet 2 were used just under 40 times and 3 were used five or fewer times.  One has to question why these protocols exist and on what basis is staff choosing the infrequently used protocols.

This creates several issues, from hanging protocols in PACS to patient safety issues.  For example, when it is time to alter the protocol will whomever is updating the scanner parameters really change all 7 protocols?  This is important as facilities review their Dose reports and begin to make protocols changes to lower patient doses.

This is a widely recognized issue within the industry.  In its 2016-2017 development cycle Integrating the Healthcare Enterprise (IHE) is developing a new profile titled Enterprise Scanner Protocol Management to address this very issue.  Click here for more information on IHE’s initiative.

The good news is that because of the information contained in our reports, we are able to help them identify and eliminate duplicate and superfluous scanner protocols.


Need help getting more from your participation in the ACR’s Dose Index Registry® ?  Let Dose Registry Support Services tailor a program designed specifically to help your department succeed.  Contact Dose Registry Support Services to see how we can help.

 

 

Posted on 2 Comments

Joint Commission Confirms Facilities Need an Expected Dose Range for All CT Protocols; Note to Self: XR-29 Does NOT Equal TJC Compliance

The following question was submitted to the Joint Commission:

Must we establish an expected dose range for every imaging protocol or can we pick and choose the protocols for which we establish expected dose ranges and monitor only those? I interpret [PI.02.01.01.A.6.] to require monitoring of every protocol we use, not just some portion of them.

The Joint Commission response:

All protocols need to have an expected dose index range included. For protocols that are of similar anatomical areas, I have suggested that a general range (like the AAPM alert levels or ACR Pass/Fail levels) be used. As data is collected, analyzed and benchmarked then the expected dose index range can be refined.

Associate Director Standards Interpretation Group, Standards Interpretation Division of Healthcare Improvement Group The Joint Commission

—————————-

Dose Registry Support Services Discussion: The reason we asked this question is to confirm my suspicion that XR-29, by itself, does not meet TJC’s dose incident identification requirement UNLESS facilities enter a dose range for every protocol they use, AND THEN have the ability to check the dose threshold UPON COMPLETION of the exam, which is much different than the XR-29 which often only test a subset of protocols and issues pre-scan alerts or notifications. Additionally, most XR-29 solutions do not establish a lower threshold in the system.  By definition, a “range” requires both an upper and lower threshold.  This was also confirmed with TJC during RSNA.  In summary, be very careful if you plan to depend solely on your scanner’s XR-29 capabilities to meet TJC’s Dose Incident Identification requirements.  It may not be set up to test doses on every protocol you use.

We have developed an effective, low cost solution for establishing both an upper and lower threshold dose range as well as identifying “dose Incidents” in which an exam exceeded the threshold.  The only requirement:  Participation in the ACR’s Dose Index Registry.  Contact us to learn more.