[Intl_DxMedPhys] ACR CT test question

Mon Sep 14 16:42:28 EDT 2026

That's good to hear, that's the practice I've been using. But I have never found a good reference for correlating the abdomen diameter (21 cm?) with 70 kg.

Matt Wait, MS, DABR, DABSNM, MRSE
Senior Diagnostic Physicist

Associate Radiation Safety Officer

Assistant Residency Director

Kaiser Permanente

Southern Permanente Medical Group

Medical Imaging Technology and Informatics
4867 Sunset Blvd

Los Angeles, CA 90027

x5347 (office)

(818) 232-2427 (mobile phone)

________________________________
From: Douglas Pfeiffer <xraydoug at me.com>
Sent: Monday, September 14, 2026 1:35 PM
To: Matt Wait <Matt.Wait at kp.org>
Cc: DxMedPhys List <intl_dxmedphys_wd_osu_list at lists.osu.edu>; Bob Kobistek <bob at rjkmedphys.com>
Subject: Re: [Intl_DxMedPhys] ACR CT test question

Going through the list of scanned patients on the scanner and looking for abdomens that look about the right size, and looking at the mA at mid-liver (belly button-ish).

Best regards,
Doug

Douglas Pfeiffer, MS, DABR FACR, FAAPM (he/him)
Medical Physicist, Radiation Safety Officer
Boulder Community Health
xraydoug at me.com
303.415.7515

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The opinions expressed in this message are the product of the gray and white matter loitering in my cranium. I speak for myself and no one else, unless I say otherwise.

On Sep 14, 2026, at 2:16 PM, Matt Wait <Matt.Wait at kp.org> wrote:

Doug, how did you envision determining the automatic tube current selection for Standard Man?

Matt Wait, MS, DABR, DABSNM, MRSE
Senior Diagnostic Physicist
Associate Radiation Safety Officer
Assistant Residency Director
Kaiser Permanente
Southern Permanente Medical Group
Medical Imaging Technology and Informatics
4867 Sunset Blvd
Los Angeles, CA 90027
x5347 (office)
(818) 232-2427 (mobile phone)

________________________________
From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces+matt.wait=kp.org at lists.osu.edu<mailto:intl_dxmedphys_wd_osu_list-bounces+matt.wait=kp.org at lists.osu.edu>> on behalf of Douglas Pfeiffer via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list at lists.osu.edu<mailto:intl_dxmedphys_wd_osu_list at lists.osu.edu>>
Sent: Monday, September 14, 2026 1:12 PM
To: Bob Kobistek <bob at rjkmedphys.com<mailto:bob at rjkmedphys.com>>
Cc: DxMedPhys List <intl_dxmedphys_wd_osu_list at lists.osu.edu<mailto:intl_dxmedphys_wd_osu_list at lists.osu.edu>>
Subject: Re: [Intl_DxMedPhys] ACR CT test question

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For what it’s worth now, the intent when I was working on the manual was Standard Man (i.e., 70 kg). It was an unfortunate oversight on my part that I did not catch that and state it explicitly way back when. I’m not sure what is assumed now by the ACR, but that was the original thinking.

Best regards,
Doug

Douglas Pfeiffer, MS, DABR FACR, FAAPM (he/him)
Medical Physicist, Radiation Safety Officer
Boulder Community Health
xraydoug at me.com
303.415.7515

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The opinions expressed in this message are the product of the gray and white matter loitering in my cranium. I speak for myself and no one else, unless I say otherwise.

On Sep 9, 2026, at 1:45 PM, Bob Kobistek via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list at lists.osu.edu> wrote:

Hi.

I also beat my head against a wall searching for answers to these questions when the ACR CT accreditation program was started. I stopped overthinking it, and now I pretty much wing it.

For average size patient, I look through patient scans to find one with an A-P dimension through the abdomen of around 23 cm. If I can find more than one (hard to find nowadays), I’ll toss out the outliers and take an average of the mAs values.

For new scanners I use nearly all the options you presented. If it’s a scanner with a similar model in use at the facility, I refer to patients scanned on the existing scanners. If it’s a scanner that I see at other facilities, I’ll make adjustments for differences in protocols and use that. If it’s a scanner I’ve never seen before, I’ll pull up the manufacturer’s suggested protocols and take a guess at the mAs when TCM is used. If I use the second or third option, I’ll take a look at patient scans once the scanner has been operating for a few weeks. If I can make adjustments to my measurements based on the clinical data, I will. If I have to, I’ll repeat the measurements using the clinical protocols. If the site is going to be ACR accredited I will always make a second trip so I can use the actual protocols and clinical mAs values for accreditation, not matter which of the three options above that I use.

There is very little guidance on how to chose mAs (and kVp when applicable) for automated technique selection. So we use out best judgment.

Robert J. Kobistek, MS, FACR, DABR, MRSE(MRSC™)
Medical Physicist
RJK Medical Physics, Inc.
440-463-7879

From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces at lists.osu.edu<mailto:intl_dxmedphys_wd_osu_list-bounces at lists.osu.edu>> On Behalf Of David S. Winter via Intl_dxmedphys_wd_osu_list
Sent: Monday, September 7, 2026 4:02 PM
To: DxMedPhys List <intl_dxmedphys_wd_osu_list at lists.osu.edu<mailto:intl_dxmedphys_wd_osu_list at lists.osu.edu>>
Subject: [Intl_DxMedPhys] ACR CT test question

All, I apologize as this has no doubt been discussed in the past, but I have a two part inquiry related to ACR CT testing. I am happy to clarify directly with the ACR, but I figured I would touch base with this forum first. (Especially since
All,

I apologize as this has no doubt been discussed in the past, but I have a two part inquiry related to ACR CT testing. I am happy to clarify directly with the ACR, but I figured I would touch base with this forum first. (Especially since only part 1 would be good to ask the ACR directly.)

Part 1:  The ACR’s scanning instructions webpage and the CT QC manual both give a weight range for the pediatric abdominal exam of 40-50lbs, but only the QC manual has a weight for the adult abdomen (i.e. 70 kg, ~154 lbs). The webpage merely says “average sized patient”. The exclusion of the 70 kg reference could be an accidental omission, but that requires the same omission to have been repeated in multiple different locations on their webpage.

“Average sized” could be interpreted to mean average across the entire US population, the region a CT scanner is in, or the specific patient population a specific CT scanner sees (which could be massively different if the scanner is the go-to scanner for bariatric patients.) The CDC says the current adult average weights are 199 lbs for men and 171.8 lbs for women. (Both significantly more than 154). In addition, the ACR’s mandatory dose calculation sheet calculates the adult abdomen SSDE for a 35 cm water equivalent diameter. While you can’t exactly convert abdominal water equivalent diameter to a patient weight, that value would likely correspond to a patient significantly heavier than 154 lbs.

Has anyone specifically seen anything that dictates which is definitively correct for determining what techniques to set, and by extension, determine whether or not the scanner is really passing the CNR test?

Part 2: In practice, I am curious how people are determining the mA that CT scanners are selecting for the “average”, particularly for brand new scanners without much/any historic patient data. I can imagine four different general approaches. 1) Analysis of historical data aggregated by a dose metric monitoring system like Radimetrics. 2) Manually looking for a few historical patients that look to be roughly “average size” and then averaging the mA from a representative slice from a few of those studies. 3) For new systems, using values from a similar system with similar settings. 4) Conducting scans of a standard (e.g. their CTDI phantom), seeing what the CT scanner picks for mA, and then applying a scaling factor to that mA to adjust for the size difference.

Sincerely,
Scott

D. SCOTT WINTER

CHIEF DIAGNOSTIC MEDICAL PHYSICIST
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