[Intl_DxMedPhys] [EXTERNAL] Re: Dosimeter calibrations - question/PSA

Tue Aug 11 17:32:35 EDT 2026

Dear Everyone,

I am actually in the process of purchasing a second RaySafe and already have a direct contact with the Atlanta regional team, so I reached out about this issue. They shared a few suggestions that I thought I’d pass along, although I assume we’ve already tried most of them.

Quick Troubleshooting Checklist

  *   Check the Extension Tube (Luminance vs. Illuminance)
The RaySafe Xi Light Detector automatically switches between luminance (\(cd/m^2\)) and illuminance (\(lux\)) depending on whether the black optical extension tube is physically attached. If you are trying to measure screen luminance (\(cd/m^2\)) but the tube is detached or not fully seated, the sensor acts as an ambient illuminance meter. This completely skews the geometry of the light entering the photodiode, dropping your reading significantly. Ensure the tube is securely clicked into place for contact measurements.
  *   Verify the Sensor Menu Setting
The RaySafe system requires you to specify the target light source in the SENSOR MENU to apply the proper internal photopic correction factors.
     *   Turn on the base unit and navigate to the SENSOR MENU.
     *   Ensure you have selected the correct category (e.g., LuminanceLCD, LuminanceCRT, or a specific brand profile like Barco). Selecting a generic setting for a highly specialized or filtered medical monitor can result in scaling discrepancies.
  *
Confirm the Unit Mode (\(cd/m^2\) vs. \(fL\))
Ensure the meter is actually set to display metric \(cd/m^2\) and has not been changed to Imperial Foot-lamberts (\(fL\)) in the SETUP MENU. While the conversion factor between the two units is roughly \(3.43\) (not exactly \(10\)), an unexpected unit switch combined with a dim display can easily look like a factor-of-ten calculation error.
  *
Perform a Manual Zero-Offset Adjustment
If you are measuring very low luminance levels (near or below \(2\ cd/m^2\)), the baseline dark current can skew the fractional display. Cover the sensor completely with its cap or a light-tight cloth, go to the menu, and execute a manual offset adjustment to reset the baseline.

Best regards,
Rasha Makkia, Ph.D., DABR
Section Chief, Diagnostic Medical Physics
Assistant Professor of Radiology | Diagnostic Medical Physicist
Department of Radiology & Imaging
Medical College of Georgia at Augusta University / Wellstar MCG Health Medical Center
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Subject: [EXTERNAL] Re: [Intl_DxMedPhys] Dosimeter calibrations - question/PSA

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Thank you for posting this! We had exactly the same issue. Calibrated in July 2026. Calibration papers show calibrated at 500 and 50 cd/m2 and was within 2-3%. But when we took it out to our first site it was measuring at about what you stated,

Thank you for posting this!  We had exactly the same issue.  Calibrated in July 2026.   Calibration papers show calibrated at 500 and 50 cd/m2 and was within 2-3%.

But when we took it out to our first site it was measuring at about what you stated, 1/10th of what it should.

We initiated a RMA and are sending it back.  Yes, there must be an issue at the calibration lab.

There are probably others out there, so I’m glad you mentioned this.

Jeremy L. Corwin, MHP, DABHP

Medical Physicist

Phone: (360) 736-6066 / Fax: (360) 736-7293

https://urldefense.com/v3/__http://www.corwinhp.com__;!!KGKeukY!zOl6k1ia1_8nPL9JwRASYEjiOv5sy5eCptMprDRawc6PRveyEhAFL9k-rgHrKdq9EBQ3J2iLnikfboT2dlCBqMlC3vz-lH7-3PbAsx1uvQ$ <https://urldefense.com/v3/__http://www.corwinhp.com__;!!KGKeukY!2TymMTWhwKC0NgLZf62WF9DJcu3Gpv_K9BjqKjpsbg9CmiKijD-srFkZts-H0kchkK4AI11xSRd1A5K7860KiiIwVyee0mbfrQTq-ps$>

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From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces+jeremy=corwinhp.com at lists.osu.edu> On Behalf Of Milman, Rebecca via Intl_dxmedphys_wd_osu_list
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Subject: [Intl_DxMedPhys] Dosimeter calibrations - question/PSA

Hi, colleagues, I have a combined question/PSA about RaySafe measurement devices. We recently received an Xi back from calibration, and the luminance meter was calibrated incorrectly (by a factor of 10). Is anyone else having issues with this?

[cid:image002.png at 01DD2977.86EBF2C0]

Hi, colleagues,

I have a combined question/PSA about RaySafe measurement devices. We recently received an Xi back from calibration, and the luminance meter was calibrated incorrectly (by a factor of 10).

Is anyone else having issues with this? Also (the PSA part!) our calibration report indicated everything had passed. The calibration report said it was tested (and measured) post-calibration at 50 cd/m^2 and passed (despite it typically being calibrated at 500 cd/m^2). Something in the calibration report is incorrect, which is especially concerning. (FWIW, we contacted RaySafe about this a week ago but still have not heard anything other than that the case is being directed to their service department.)

Thanks,

Rebecca.

Rebecca Milman, Ph.D., DABR

Division Chief, Radiological Sciences | Associate Professor

Department of Radiology

University of Colorado Anschutz

720.848.6625

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