What does this research mean for the field?

The optical density of EBT4 radiochromic films increases over time after irradiation, with significant growth occurring within the first 12 hours post-irradiation. Novelty: ClaimNovelty.CONFIRMATORY. Consensus alignment: ConsensusAlignment.SUPPORTS_CONSENSUS.

What question did this study set out to answer?

The goal is to evaluate how the optical density of EBT4 radiochromic films changes over time after radiation exposure.

February 21, 2026Open Access

On temporal evolution of the response of EBT4 radiochromic films

Key Points

The goal is to evaluate how the optical density of EBT4 radiochromic films changes over time after radiation exposure.
Irradiated EBT4 film samples with varying doses using a clinical linear accelerator.
Performed repeated scans using a flatbed scanner over approximately two months after irradiation.
Measured net optical density and established sensitivity and calibration curves at different time points.
Optical density increased over time across all color channels, though the growth rate reduced with higher doses.
Red channel OD grew by ∼8%–30% for films at 15-1 Gy over the study period; green channel showed similar trends with slightly higher growth rates.
Films exposed to doses > 1 Gy reached approximately 90% of final OD within the first 12 hours after irradiation.

Abstract

Abstract Background Radiochromic film dosimeters are commonly used in radiation oncology in both clinical and research settings to measure the radiation dose with high spatial resolution over a two‐dimensional area. Radiation‐induced solid‐state polymerization occurring in films leads to a change in their opacity. It is critical to evaluate the temporal stability of the response of new film models to ensure an appropriate post‐irradiation time is selected for film scanning. Purpose To investigate the time‐dependent growth of optical density (OD) in the recently released EBT4 radiochromic films. Methods EBT4 film samples were irradiated at 0.125, 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, and 15 Gy dose levels using a 6 MV X‐ray beam produced by a clinical linear accelerator. Two film samples were irradiated at each dose level. The films were repeatedly scanned using a flatbed scanner upon irradiation and at various time intervals for approximately 2 months (1325 h). The net OD was measured, and the films’ sensitivity and calibration curves were obtained at several time points. Results The net OD grows with time in all color channels, the rate of which reduces with dose. Red channel OD increased by ∼8%–30% over the studied time period for films irradiated at 15‐1 Gy. A similar trend was observed in the green channel with slightly higher (∼1%–2%) growth rates compared to the red channel. Films irradiated at > 1 Gy dose reached over ∼90% of their final net OD within the first 12 h post‐irradiation, followed by a gradual growth over the following weeks. The OD‐per‐Gy decreased with dose and increased with elapsed time post‐irradiation. Conclusion Since the response of the films continues to develop with time, to adhere to good practice of film dosimetry, the calibration and test films must be read at the same time interval post‐irradiation, otherwise significant errors in dose measurement can occur. Since the temporal dynamics of EBT4 and EBT3 films were found to be similar, both models can be treated similarly in terms of the optimum post‐irradiation wait‐time prior to film readout.

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