Storage Temperature and Humidity Effects on Dose Evaluation with Radiochromic Films (Gafchromic EBT-XD and EBT4)

<div> In an emergency, radiochromic films hold great promise as portable radiation dosage monitors. However, exposure to heat or moisture before irradiation may significantly skew dose estimates, and their dosimetric response is by no means immune to environmental factors. We carried out a methodical series of pre-irradiation storage experiments under controlled temperature and humidity conditions to characterise the effects of two commercially available film types: Gafchromic EBT-XD and EBT4. Film samples (35 x 25 mm2) were kept in a CO2 incubator for 72 hours at 20, 30, 35, and 40 C with a relative humidity (RH) of no more than 50%. All study samples were exposed to X-rays (160 kVp, 6.3 mA) at doses ranging from 2.5 to 20 Gy. A flatbed scanner was used to capture RGB images, and a spectrophotometer was used to record absorbance spectra.
 </div> <div> <br> </div> <div> When compared with reference films kept at 20 C, both types of films showed moderate changes in net optical density (OD) under dry, elevated-temperature conditions (30–40 C, less than 30 per cent relative humidity). The measured dosages were much lower than the supplied values when these 20 °C reference films were used as controls. EBT4 has a larger deficit than EBT-XD. In comparison, with the same thermal history, unirradiated films were used as controls, and the dosimetry values for the evaluated doses were found to be close to the delivered values for the same type, demonstrating the decisive importance of selecting control samples for accurate dosimetry of both types. </div> <div> <br> </div> <div> The same effect was observed in highly humid storage (35 C, 90% RH): both types of films showed a significant increase in OD values, and even when control films kept under the same incubator conditions were used to calculate the values, the dose estimate was significantly overestimated. These findings suggest that, independent of any actual dose effect, the process of water vapour infiltration into the active layer increases the apparent radiation response and promotes additional polymerisation. The findings collectively indicate that humidity should be monitored and kept under strict control, just as temperature, when using such films in changing field conditions that are not under control, and that vacuum-sealed packaging should be adopted whenever uncontrolled ambient conditions are expected. </div>