[Intl_DxMedPhys] X-ray Meter Calibration Overseas

[Christopher Passmore]

Hello,

I think the question is how are the units calibrated? Do they send "golden
or reference" units to be calibrated and then they are used to calibrate
the other units or is an ionization chamber being used that is directly
traceable? When a laboratory uses a golden calibration unit — whether an
ionization chamber, reference dosimeter, or other master standard — it is
participating in a widely recognized metrological practice for transferring
traceability to working instruments. The validity of this practice depends
entirely on the golden unit’s own documented calibration history, including
an unbroken chain of comparisons to SI units through a National Metrology
Institute (NMI) such as NIST or PTB. This framework aligns with
international requirements established under the CIPM Mutual Recognition
Arrangement (CIPM MRA), which provides the mechanism through which NMIs
demonstrate equivalence of their calibration and measurement capabilities
and the certificates they issue. When a golden unit is used within its
characterized uncertainty limits and supported by proper documentation, any
calibration derived from it legitimately inherits the traceability of the
NMI that calibrated the golden unit.

However, the use of golden units also introduces important distinctions
that auditors and regulators will examine. NIST explicitly states that
metrological traceability exists only when there is a clearly documented,
unbroken chain of calibrations to a recognized reference standard, and that
traceability to another NMI (such as PTB) does not automatically constitute
“NIST traceability” unless the golden unit itself has been directly
calibrated by NIST. Under the CIPM MRA, PTB and NIST mutually recognize
each other’s calibration and measurement capabilities, and users may deem
these equivalent for practical purposes. But NIST policy requires that
traceability claims remain tied to the specific NMI that performed the
calibration, not to NIST by association alone. This is why it matters
whether the golden unit is calibrated directly by NIST or another MRA
signatory.

Because traceability is fundamentally about documentation, uncertainty
analysis, stability, and calibration lineage, regulators will look closely
at who calibrated the golden unit, whether the calibration certificate is
from an accredited NMI or laboratory, and whether each transfer step is
properly controlled. A PTB-calibrated golden unit may provide
internationally recognized SI traceability under the CIPM MRA, and in many
contexts this is sufficient. But it is not technically “NIST-traceable”
unless NIST provided the calibration of the golden unit. Understanding this
distinction — and documenting the calibration chain correctly — is
essential for compliance programs such as MQSA, ISO/IEC 17025
accreditation, and any process where formal traceability claims must
withstand regulatory or contractual scrutiny.

It's been awhile but I think you can find these references in NIST guidance
document GMP 13: Good Measurement Practice for Ensuring Metrological
Traceability, Metrological Traceability Frequently Asked Questions and NIST
Policy (NIST P 5800.00), and NIST Technical Note (NIST ­TN 2156). I don't
think that NIST has changed these requirements, but if I'm incorrect please
let me know.

On Mon, Dec 8, 2025 at 1:29 PM Little, Kevin via Intl_dxmedphys_wd_osu_list
<intl_dxmedphys_wd_osu_list at lists.osu.edu> wrote:

> Raysafe has this explanation of how their German/European PTB traceability
> is equivalent to NIST:
>
> https://urldefense.com/v3/__https://www.raysafe.com/sites/default/files/22885_452_PTB_NIST_Flyer.pdf__;!!KGKeukY!3gEWKuPfI38gMRbviPMZYLXWqtfUxduZ6FgX3F1ptAONuCDSzjWnHGI7SvSgo232iT2Si7_jGJH2gMn8aU5TStE4UV7RF3teOARoF4AsRmNXyl0A$ 
> <https://urldefense.com/v3/__https://www.raysafe.com/sites/default/files/22885_452_PTB_NIST_Flyer.pdf__;!!KGKeukY!wKUIZCe4jZcxYSOFQAtTMlSiz1FK5eVwqzk15Z1adZ_cOu0kW6AFhWIWKLVpWtoOn5aC7vZZpiymekHwFyP_XPaD-gpnfmOHsAKbriu-ywZfdOM$>
>
>
>
> Raysafe’s general conclusion is that both NIST and PTB have signed the
> International Committee for Weights and Measures (CIPM) Mutual Recognition
> Arrangement (https://urldefense.com/v3/__https://www.bipm.org/en/cipm-mra__;!!KGKeukY!3gEWKuPfI38gMRbviPMZYLXWqtfUxduZ6FgX3F1ptAONuCDSzjWnHGI7SvSgo232iT2Si7_jGJH2gMn8aU5TStE4UV7RF3teOARoF4AsRnV5InRl$ 
> <https://urldefense.com/v3/__https://www.bipm.org/en/cipm-mra__;!!KGKeukY!wKUIZCe4jZcxYSOFQAtTMlSiz1FK5eVwqzk15Z1adZ_cOu0kW6AFhWIWKLVpWtoOn5aC7vZZpiymekHwFyP_XPaD-gpnfmOHsAKbriu-USJtgfA$>).
> According to the website for this arrangement, “The CIPM Mutual Recognition
> Arrangement (CIPM MRA) is the framework through which National Metrology
> Institutes demonstrate the international equivalence of their measurement
> standards and the calibration and measurement certificates they issue.”
> Both NIST and PTB participate in this MRA:
> https://urldefense.com/v3/__https://www.bipm.org/en/cipm-mra/participation__;!!KGKeukY!3gEWKuPfI38gMRbviPMZYLXWqtfUxduZ6FgX3F1ptAONuCDSzjWnHGI7SvSgo232iT2Si7_jGJH2gMn8aU5TStE4UV7RF3teOARoF4AsRiAatOsX$ 
> <https://urldefense.com/v3/__https://www.bipm.org/en/cipm-mra/participation__;!!KGKeukY!wKUIZCe4jZcxYSOFQAtTMlSiz1FK5eVwqzk15Z1adZ_cOu0kW6AFhWIWKLVpWtoOn5aC7vZZpiymekHwFyP_XPaD-gpnfmOHsAKbriu-vQ9NXf4$>,
> https://urldefense.com/v3/__https://www.nist.gov/calibrations/cipm-mutual-recognition-arrangement__;!!KGKeukY!3gEWKuPfI38gMRbviPMZYLXWqtfUxduZ6FgX3F1ptAONuCDSzjWnHGI7SvSgo232iT2Si7_jGJH2gMn8aU5TStE4UV7RF3teOARoF4AsRvEUrPjL$ 
> <https://urldefense.com/v3/__https://www.nist.gov/calibrations/cipm-mutual-recognition-arrangement__;!!KGKeukY!wKUIZCe4jZcxYSOFQAtTMlSiz1FK5eVwqzk15Z1adZ_cOu0kW6AFhWIWKLVpWtoOn5aC7vZZpiymekHwFyP_XPaD-gpnfmOHsAKbriu-VLvlU44$>.
> Both have been approved within the CIPM MRA for air kerma
> <https://urldefense.com/v3/__https://www.bipm.org/kcdb/cmc/search?domain=RADIATION&areaId=9&keywords=x-ray&specificPart.branch=32&specificPart.quantity=6&specificPart.medium=-1&specificPart.source=-1&specificPart.nuclide=&_countries=1&countries=21&countries=77&publicDateFrom=&publicDateTo=&unit=-1&minValue=&maxValue=&minUncertainty=&maxUncertainty=__;!!KGKeukY!wKUIZCe4jZcxYSOFQAtTMlSiz1FK5eVwqzk15Z1adZ_cOu0kW6AFhWIWKLVpWtoOn5aC7vZZpiymekHwFyP_XPaD-gpnfmOHsAKbriu-DZDT4cM$>.
> NIST and PTB also published a direct comparison for mammography in 2009:
> https://urldefense.com/v3/__https://pmc.ncbi.nlm.nih.gov/articles/PMC4646528/__;!!KGKeukY!3gEWKuPfI38gMRbviPMZYLXWqtfUxduZ6FgX3F1ptAONuCDSzjWnHGI7SvSgo232iT2Si7_jGJH2gMn8aU5TStE4UV7RF3teOARoF4AsRkKC5APj$ 
> <https://urldefense.com/v3/__https://pmc.ncbi.nlm.nih.gov/articles/PMC4646528/__;!!KGKeukY!wKUIZCe4jZcxYSOFQAtTMlSiz1FK5eVwqzk15Z1adZ_cOu0kW6AFhWIWKLVpWtoOn5aC7vZZpiymekHwFyP_XPaD-gpnfmOHsAKbriu-25YDAQ4$>
> .
>
>
>
> NIST says traceability to another National Metrology Institute (NMI)
> doesn’t automatically mean something is NIST-traceable (
> https://urldefense.com/v3/__https://www.nist.gov/metrology/metrological-traceability*:*:text=5.5.2__;I34!!KGKeukY!3gEWKuPfI38gMRbviPMZYLXWqtfUxduZ6FgX3F1ptAONuCDSzjWnHGI7SvSgo232iT2Si7_jGJH2gMn8aU5TStE4UV7RF3teOARoF4AsRkKkEH3T$ 
> <https://urldefense.com/v3/__https://www.nist.gov/metrology/metrological-traceability*:*:text=5.5.2__;I34!!KGKeukY!wKUIZCe4jZcxYSOFQAtTMlSiz1FK5eVwqzk15Z1adZ_cOu0kW6AFhWIWKLVpWtoOn5aC7vZZpiymekHwFyP_XPaD-gpnfmOHsAKbriu-C0BH4Uo$>),
> but “users of measurement results, who may be either commercial or
> regulatory entities, may well decide that sufficient evidence exists under
> the MRA to provide mutually acceptable traceability of these results to the
> standards and measurements of two or more participating NMIs.”
>
>
>
> So, I agree that it might be nice to get an “official” recognition of
> Raysafe’s logic from the MQSA hotline.
>
>
>
> Kevin Little
>
> Ohio State University
>
>
>
>
>
>
>
> *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:* Monday, December 8, 2025 11:44 AM
> *To:* Michael Urgo <murgo571 at verizon.net>;
> intl_dxmedphys_wd_osu_list at lists.osu.edu
> *Subject:* Re: [Intl_DxMedPhys] X-ray Meter Calibration Overseas
>
>
>
> You might want to contact the MQSA hotline and inquire about this. Doing
> so could motivate the FDA to create an alternative standard. There’s no
> practical reason why traceability to a European standard agency would not
> be acceptable. Robert
>
> You might want to contact the MQSA hotline and inquire about this. Doing
> so could motivate the FDA to create an alternative standard. There’s no
> practical reason why traceability to a European standard agency would not
> be acceptable.
>
>
>
>
>
> 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+bob=rjkmedphys.com at lists.osu.edu> *On
> Behalf Of *Michael Urgo via Intl_dxmedphys_wd_osu_list
> *Sent:* Friday, December 5, 2025 7:24 AM
> *To:* intl_dxmedphys_wd_osu_list at lists.osu.edu
> *Subject:* [Intl_DxMedPhys] X-ray Meter Calibration Overseas
>
>
>
> Happy Friday. I was thinking about this in reference to overseas
> calibration. I checked the MQSA (CFR 21 part 900) regs again, and they are
> very specific about a NIST traceable calibration lab. See attached
> screenshots for national standard
>
> Happy Friday.  I was thinking about this in reference to overseas
> calibration.  I checked the MQSA (CFR 21 part 900) regs again, and they are
> very specific about a NIST traceable calibration lab.  See attached
> screenshots for national standard calibration and definition.  Does anyone
> know if any overseas labs participates with NIST?  Of course the
> calibration certificate lists their national standard.  Thanks for any info
> you can provide.   Donna Davis-Urgo
>
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