Fricke Gel Dose Indicators Applicable for Blood Irradiators

Introduction: Transfusion of irradiated blood is recommended by the guidelines for cardiosurgery, cancer surgery, severe trauma and congenital immune deficient recipients. To prevent post- transfusion graft-versus-host disease (PT-GVHD), blood cells may be irradiated by gamma rays. The absorbed dose range for blood irradiation is typically 15 to 50 Gy. As the assurance that blood has been properly irradiated plays an important role for patient health, appropriate gamma dosimetry has to be performed. So, Fricke gel dosimeters in a dose range from 10 to 50 Gy were constructed in this study. Using optical absorption of the gel, the absorbed dose can be determined accurately. Furthermore, the gel can be used as a radiation indicator.
 
Materials and Methods: The gelling agent powder was added to a beaker containing distilled water. It was then boiled until a clear solution was obtained. Ferrous ammonium sulphate solution containing a metal indicator and sulphuric acid was added. The gel was then poured into cuvettes and left for half an hour before irradiation. Irradiation was done by Gammacell- 220 at 10, 20, 30, 40 and 50 Gy. The optical absorption of the gel was specified using a BECKMAN COULTER-DU-800 spectrophotometer.
Results: Frick gel samples present two absorption bands: one at range from 435 to 445 nm, corresponding to Fe2+ ions initially present in the unirradiated gel and other at range from 575 to 585 nm corresponding to Fe3+ ions generated by radiation induced Fe2+ ions oxidation. The first band tends to disappear depending on the absorbed dose as the second band is intensified with increasing dose. Dose response curve clearly indicates linear range of 10 to 50 Gy.
The color change started immediately after irradiating and was fully developed within thirty minutes. The irradiated region is clearly seen as a blue zone against the unirradiated yellow- orange background. As dose increased from 10 to 50 Gy, the color intensity of the samples was enhanced. The color change showed no visible diffusion for at least five days. If care is taken to follow the gel preparation procedure, the color change produced by radiation is quite reproducible with a low variability.
Conclusion: Fricke gel dosimeters have many appealing features. They are tissue equivalent over a large photon energy range, easily prepared in any shape and are readily analyzed by optical techniques after irradiation. These advantages together with dose indication that enable one to probe the radiation dose more quickly shows that Fricke gel dosimetry has a continuing role in clinical applications. We are working on the development of Fricke gel dosimeters by adding specific dopants to increase the dose sensitivity and uniformity of gel preparation.