Humidity effects in GafChromicTMEBT4 films for postal audits: characterization, reversibility and exploration of correction methods
In brief
Humidity shifts EBT4 readings, but effects reverse after re-acclimatization
Humidity changed EBT4 film optical density and dose response, creating potentially significant dosimetry errors if ignored. Between 12% and 68% relative humidity, these effects were reversible after films were re-acclimatized, and zero-dose control films reduced humidity-related offsets. Proposed film-based correction proxies still need validation across film lots and scanners, so controlling humidity in transport and storage remains important.
- Journal
- Physics in medicine and biology (Q1)
- Published
- 2 October 2026
- Study design
- Unclassified
- Evidence level
- Level 5, Expert Opinion (CEBM 5)
- Authors
- Leon Armand de Prez
- PMID
- 42826741
- DOI
- 10.1088/1361-6560/aeafa7
Why clinicians should know about it
- Picked for Medical Physics (paper of the day, 3 October 2026): Humidity effects on EBT4 film dosimetry characterized
Abstract
No harmonized methodology exists that enables traceable reference dosimetry with EBT4-film. The influence of humidity on EBT4 films is often overlooked and currently under-documented. This study quantified humidity effects for postal-audit reference dosimetry and explored the feasibility of empirical correction methods.
Approach. EBT4 films mounted in slide-frames were stored in humidity-controlled environments between 0 %RH and 100 %RH and scanned using a slide-scanner. Optical density (OD) was evaluated as a function of dose and humidity. Humidity darkening, changes in dose response and post irradiation growth were quantified. A humidity response factor, HOD, was introduced to describe the humidity dependent changes in dose-response. Two film intrinsic proxies were evaluated as possible proxies for the film humidity state.
Main results. Humidity was shown to affect OD and the humidity response factor, HOD. If not accounted for, this can lead to significant dosimetric errors. Between 12 %RH and 68 %RH, HOD exhibited linear behaviour as did the two film intrinsic proxies. Both humidity darkening and HOD showed to be reversible within the experimental uncertainty after re-acclimatization at 56 %RH. Exposure to 0 %RH and 100 %RH resulted in behaviour outside the practical operating range. The use of 0-Gy control films substantially reduced humidity-dependent offsets. The film-intrinsic humidity proxies showed relationships with HOD within the present single-sheet experiment, but their practical use requires further validation across film-lots and scanners.
Significance. This study demonstrates that humidity is a relevant influence quantity for EBT4-based reference dosimetry and should be controlled during film transport and storage. For the VSL postal audit service, humidity is regulated using BOVEDA-49 packages and monitored during transport as a practical mitigation strategy. The proposed correction formalism provides a method to investigate humidity-response behaviour for a specific film-sheet and scanner combination but does not yet constitute a generally validated correction method.
Abstract as published, via PubMed.
For healthcare professionals. The summary is generated by AI from the published abstract, and the evidence level is assigned automatically from the study design on the Oxford CEBM hierarchy. Neither is medical advice. Read the full paper before changing practice.