SU-FF-T-355: Preliminary Evaluation of Optically Stimulated Luminescence (OSL) Dosimetry for Small Field High Energy Photon Beam

Abstract

Purpose: Small field high energy photon beams, frequently used in stereotactic radiosurgery and intensity modulated radiation therapy, are characterized by steep dose gradient and lack of lateral electronic equilibrium. Small field dosimetry requires special detectors, such as diamond detector, micro-ionization chambers, or diode detectors. In the present study the feasibility of using Optically Stimulated Luminescence (OSL) dosimetry in small field 6MV photon beam was investigated. Methods and Materials: The performance of the OSL in this study was evaluated using absolute and depth dose measurements for small fields of 1×1, 2×2 and 4×4cm2 with detectors placed in a water tank at the central axis perpendicular to the beam. OSL detectors disks with diameter of 3mm) and an #a16 Exradin microcylindrical ionization chamber (EMIC) were used to evaluate the depth dose distributions of smaller fields. The depth dose distributions for field sizes of 4×4 and 10×10cm2 measured by EMIC were cross-compared and verified by Scanditronix CC13 ionization chamber for the Varian 21EX linear accelerator. Depth dose distributions measured by OSL for small field sizes of 1×1, 2×2 and 4×4cm2 were then compared to those acquired by EMIC. Results: For the 4×4 and 10×10cm2 field sizes, the EMIC data are in excellent agreement with the CC13 ionization chamber data. When compared the depth dose curves obtained using the OSL techniques against the EMIC data, the difference was ⩽ 1.9%, 0.9% and 1.9% for 1×1, 2×2, 4×4cm2 respectively, for depths between 10 mm to 150 mm. The data are currently being analyzed and will be presented. Conclusion: This is the first time that OSL dosimeters were investigated for small field dosimetry. Preliminary results indicated that the OSL dosimeters can be used to provide accurate dose estimates and could be a promising alternative detector for small field dosimetry.