Temperature and hydration effects on absorbance spectra and radiation sensitivity of a radiochromic medium

• Published in: Medical physics (Lancaster) 2008-10, Vol.35 (10), p.4545-4555
• Main Authors: Rink, Alexandra, Lewis, David F., Varma, Sangya, Vitkin, I. Alex, Jaffray, David A.
• Format: Article
• Language: English
• Subjects: Absorption spectra; Dose-Response Relationship, Radiation; Dose‐volume analysis; dosimetry; Dosimetry/exposure assessment; environmental conditions; Equipment Design; Equipment Failure Analysis; FILM DOSIMETRY; Film Dosimetry - instrumentation; Film Dosimetry - methods; HUMIDITY; HYDRATION; Ionizing radiation; IONIZING RADIATIONS; Lithium; OPACITY; Polymer films; Polymer structure; Polymerization; Polymers; RADIATION CHEMISTRY, RADIOCHEMISTRY AND NUCLEAR CHEMISTRY; Radiation Dosage; Radiation Measurement Physics; radiation therapy; radiochromic film; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; Reproducibility of Results; SENSITIVITY; Sensitivity and Specificity; Temperature; TEMPERATURE DEPENDENCE; Temperature measurement; TEMPERATURE RANGE 0273-0400 K; Therapeutic applications, including brachytherapy; VISIBLE SPECTRA; Water - chemistry
• ISSN: 0094-2405; 2473-4209; 0094-2405
• DOI: 10.1118/1.2975483

The effects of temperature on real time changes in optical density ( Δ OD ) of GAFCHROMIC® EBT film were investigated. The spectral peak of maximum change in absorbance ( λ max ) was shown to downshift linearly when the temperature of the film was increased from 22 to 38 ° C . The Δ OD values were also shown to decrease linearly with temperature, and this decrease could not be attributed to the shift in λ max . A compensation scheme using λ max and a temperature-dependent correction factor was investigated, but provided limited improvement. Part of the reason may be the fluctuations in hydration of the active component, which were found to affect both position of absorbance peaks and the sensitivity of the film. To test the effect of hydration, laminated and unlaminated films were desiccated. This shifted both the major and minor absorbance peaks in the opposite direction to the change observed with temperature. The desiccated film also exhibited reduced sensitivity to ionizing radiation. Rehydration of the desiccated films did not reverse the effects, but rather gave rise to another form of the polymer with absorbance maxima upshifted further 20 nm . Hence, the spectral characteristics and sensitivity of the film can be dependent on its history, potentially complicating both real-time and conventional radiation dosimetry.