LASER-SCANNED AGAROSE-GEL SECTIONS FOR RADIATION-FIELD MAPPING

Purpose: A dedicated laser scanning system has been applied to the mea surement of optical density change in ferrous sulphate-xylenol orange dye-agarose gel mixtures for applications in radiation field mapping. Methods and Materials: The gels were poured, irradiated, and optically scanned in Lucite casts providing a uniform gel section thickness of 1 cm, The gel sections were optically scanned both pre- and postirradi ation to determine the optical density change in the gel and consequen tly the absorbed dose, Irradiations of the gel sections were performed with an orthovoltage unit and a linear accelerator. Results: For line ar dose response up to 10 Gy, an appropriate gel mixture was found to be 0.4 mM Fe2+, 0.2 mM xylenol orange dye, 25 mM sulphuric acid, and 1 % by weight agarose gel with a mixing temperature of 60 degrees C, In dosimetry of a 20 x 10 cm 6 MV wedged x-ray field, good agreement in t erms of relative dose was found between the gel values and ionization chamber readings, However, in repeated experiments with the gel dosime ter involving calculation of absolute dose at various points in the we dged field, variations in absolute dose measurements of up to +/- 5% m ere observed. Conclusion: The dosimetry technique involving laser scan ning of agarose gel sections has potential for further applications in radiotherapy dosimetry.