Troubleshoot Dosimeter Measurements

1 - Overview

Every measurement system has results that deviate from the process. For a B3 Dosimetry system, users must define a method for evaluating outlier measurements or dosimeter measurements that differ from the expected dose. See References:

ASTM E178 Standard Practice for Dealing with Outlying Observations.
ASTM 51649 Standard Practice for Dosimetry in an Electron Beam Facility for Radiation Processing at Energies Between 300 keV and 25 MeV.
ASTM 52628 Standard Practice for Dosimetry in Radiation Processing
ASTM 51275 Standard Practice for Use of a Radiochromic Film Dosimetry System
ANSI/AAMI/ISO 11137-3 Sterilization of health care products—Radiation—Part 3: Guidance on dosimetric aspects of development, validation and routine control

Do you use the GEX DoseControl Dosimetry System?

See GEX guidance - Investigating B3 Dosimeter Measurements

2 - General Guidance

Identify and resolve easy dosimeter measurement outliers caused by operator deviation from the established process, a dirty dosimeter, or basic operator error. Repeat the dosimeter measurement to achieve the actual result.
Reproduce the event that caused the problem. A reproduction of events will be more valuable than reliance on the memory of even the most diligent employee.
Thoroughly investigate the issue. Oftentimes, the dosimeter measurement result is accurate and reflects valuable information about an unseen or unknown problem that occurred during the irradiation process.
Large deviations (>10%) are most often the result of a deviation in the irradiation process, operator error causing a problem for the irradiation process – combined with a dosimetry operator error (example, dirt on the dosimeter film).

3 - Checklist for investigation of dosimeter measurement*

POTENTIAL CAUSE	DESCRIPTION
Deviation in the irradiation process	Dosimeter measurement is correct. The dose value, while unexpected, is the result of a problem in the irradiation process – Irradiator malfunction, conveyor malfunction, etc.
Deviation in product handling	Operator error. The product was not loaded correctly and caused the product to not be irradiated in the correct geometry to achieve the expected dose result.
Deviation in dosimeter placement	Operator error. The dosimeter was not placed in the correct position according to the user’s irradiation process.
Condition of the dosimeter	Inspect the dosimeter for physical damage. Fingerprints, oil smudges, dirt, dust, particulates on the dosimeter film can interfere with the measurement result.
Verification of heat treatment of the dosimeter	Verify the dosimeter was, in fact, heat treated correctly prior to measurement. Verify the heat treatment process is working as expected – correct temperature, duration of dosimeter time in the incubator, consistent time between irradiation and heat treatment.)
Verification of the measurement instrument (spectrophotometer, scanner)	Verify the instrument is operating as expected. (Example – When was the last instrument performance verification test completed? Is the spectrophotometer lamp at the end of life? Was the instrument warmed-up for the appropriate amount of time? Is something blocking the spectrophotometer light path?)
Verification of operator activities	Verify the person executing the dosimeter measurement followed the correct measurement process. (Example – did the operator fully insert the dosimeter sample in the holder? Did the operator zero the instrument with a sample in the holder?)
Verification of dosimetry process	Verify that your dosimeter measurement process meets the requirements for B3 dosimeter measurements. (Example – is the spectrophotometer analysis wavelength set correctly?)
Error in dose calculation	Verify that you are calculating the dose correctly. (Example – are you using the correct dosimeter batch calibration for the respective irradiation pathway, dosimeter batch ID, and measurement instrument/spectrophotometer? Is your dosimetry software calculating dose as expected?)

*This checklist is not exhaustive and intended for guidance purposes only. See ASTM E178 Standard Practice for Dealing with Outlying Observations.

4 - Investigating a B3 dosimeter issue

What is ‘damage’ to B3 film?

If damaged, the dosimeter is un-measurable. B3 film is ‘damaged’ if the film displays:

Rips, tears or cuts on the film
Severely melted plastic. A melted dosimeter may adhere to the interior of the pouch. There may be a large bubble that spans the center of the film surface.

What causes an issue with the dosimeter’s absorbance measurement?

Dirt, debris, dust, fingerprints, oil, smudges on B3 film – Gently clean the film surface and re-measure the dosimeter. See Handling B3 Dosimeters.
Dirt and debris in dosimeter holder – Maintain a regular cleaning schedule for the dosimeter measurement equipment. A dirty dosimeter holder can cause an issue for the dosimeter measurement.
- The built-up debris can cause the dosimeter to not sit fully in the holder, or the debris can contaminate the B3 film surface. Open the dosimeter holder and clean using compressed air and/or a damp cloth.
Bubbles or indentations on the film surface – A visible bubble, indentation or warped appearance of the film does not mean the film is necessarily damaged. Most bubbles and indents are small and do not interfere with the quality of the measurement. (See above regarding damage to the film).
Damage – See above. Dosimeter cannot be measured.

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