Laser-scanned agarose gel sections for radiation field mapping

A dedicated laser scanning system has been applied to the measurement of optical density change in ferrous sulphate-xylenol orange dye-agarose gel mixtures for applications in radiation field mapping.

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 postirradiation to determine the optical density change in the gel and consequently the absorbed dose. Irradiations of the gel sections were performed with an orthovoltage unit and a linear accelerator.

For linear dose response up to 10 Gy, an appropriate gel mixture was found to be 0.4 mM Fe2+, 0.2mM 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 terms of relative dose was found between the gel values and ionization chamber readings. However, in repeated experiments with the gel dosimeter involving calculation of absolute dose at various points in the wedged field, variations in absolute dose measurements of up to +/- 5% were observed.

The dosimetry technique involving laser scanning of agarose gel sections has potential for further applications in radiotherapy dosimetry.