[Intl_DxMedPhys] CT ACR Phantom lifetime

[Travis Painter]

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I too have noticed significant elevation of water values when the phantom is ice cold.  Mine also stays in my car most of the time and when the weather warms, everything is back to normal (+/-5 or better).  It's also about 20 years old so I don't know that it's an age-related issue.


____________________________________________
You can’t lean on the shovel and pray for a hole.

Travis Painter, M.S. DABR
Associates in Medical Physics
365 Waller Ave, Suite 200
Lexington, KY 40504
t.painter at ampmedicalphysics.com
Office – (216) 663-7000
Mobile – (859) 494-3186




-----Original Message-----
From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces at lists.osu.edu> On Behalf Of Bob Kobistek via Intl_dxmedphys_wd_osu_list
Sent: Tuesday, March 31, 2026 8:56 AM
To: Palmer, Matthew R. (BIDMC - Radiology) <mpalmer at bidmc.harvard.edu>; intl_dxmedphys_wd_osu_list at lists.osu.edu
Subject: Re: [Intl_DxMedPhys] CT ACR Phantom lifetime

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My phantom is also >20 y old. I live in northeast Ohio, and it lives in my car almost every day of the year. I also get inaccurate water HU readings compared to actual water, but it's been that way since the phantom was new. I've always blamed the fact that the red stuff in the phantom isn't really water. For my annual surveys, I just add a remark to my report stating that the scanner passes CT# testing using the manufacturer's water phantom.

As for ACR accreditation:  CT number failure is a minor failure. You can accumulate as many as 6 minor failures (4 if you're only applying for adult accreditation) and still pass accreditation.


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

-----Original Message-----
From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces+bob=rjkmedphys.com at lists.osu.edu> On Behalf Of Palmer, Matthew R. (BIDMC - Radiology) via Intl_dxmedphys_wd_osu_list
Sent: Tuesday, March 31, 2026 8:40 AM
To: intl_dxmedphys_wd_osu_list at lists.osu.edu
Subject: [Intl_DxMedPhys] CT ACR Phantom lifetime

I have a Gammex CT ACR phantom that's probably 20 or more years old. I've noticed recently that it's consistently reporting higher CT numbers for water than the scanner reports for the daily QC measurements on the manufacturer's phantom (actual water).  In the range of 4 - 8 HU on scanners reporting 0 HU on the DQA.  This happens on more than one scanner from more than 1 vendor.

Is it possible that my phantom has reached its best-before date?  Not sure what could be happening to the plastic but can it have become more dense over time?

Or, is temperature an issue?  We've had a cold winter here in Boston and I transport the phantom in my car and it sometimes stays there overnight.

And, is there anything I can do if I'm in a bind - say when the water is above 7 and I need to acquire a series for an ACR submission?

Matt  Palmer
BIDMC


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