Optically stimulated luminescence for diagnostic and therapeutic low to medium energy X-ray beams experimental dosimetry

Abstract

Introduction Optically stimulated luminescence (OSL) using aluminium oxide crystals (Al2O3:C) is a radiation detection technique, which has been validated as a reliable and promising alternative to ion chambers measurements in radiation therapy with significantly smaller active volumes and good tissue equivalence at diagnostic and therapeutic X-rays energies. However the precision achieved at lower energies is directly linked to the ability to characterise, model and correct the energy dependence of these detectors. The aim of this study was to characterize the OSL detectors in terms of energy dependence using monochromatic diagnostic and therapeutic beams in the low-medium energy range (25–90 keV); and to evaluate the potential of this technique for exeprimental dosimetry in radiologic and therapeutic applications at these energies. Materials and methods The OSL/OF (Optical Fibers) system is composed of a multichannel reader and OSL OFS (Optical Fibre Sensors) incorporating dosimetric-grade alumina crystals. Al2O3:C (0.09 mm3). Irradiations have been performed at the European synchrotron radiation facility medical beamline using square irradiation fields at 8 energy points from 25 to 90 keV. Absolute dose measurements have been performed at 80 keV at 2 cm depth in a water equivalent phantom. Once irradiated the detector has been read over 300 s to collect all the light available from the trapped electrons, which is directly linked to the absorbed dose. Results The OSL detector exhibit an energy dependance ranking from 10% to 45% from 25 to 90 keV. The use of the OSL detector for absolute dosimetry in a water equivalent phantom at 80 keV has shown a good reproducibility with a standard deviation lower than 5% for a 4 Gy single dose, using 5 × 5 cm2 field. Conclusion Those measurements demonstrated that the OSL energy dependance decreases with the beam energy. Moreover there is a good reproducibility in the OSL signal if being used in absolute dosimetry. The next step of this study is to use OSLD for beam penumbra caracterisation, where conventional detectors exhibit a severe energy dependance at these low energies. In vivo dosimetry applications in synchrotron stereotactic radiotherapy are also currently being investigated.