Fiber-Coupled, Time-Gated <formula formulatype="inline"> <tex Notation="TeX">${\hbox {Al}}_{2}{\hbox {O}}_{3}\!:\!{\hbox {C}}$</tex> </formula> Radioluminescence Dosimetry Technique and Algorithm for Radiation Therapy With LINACs

Abstract

An original algorithm for real-time In Vivo Dosimetry (IVD) based on Radioluminescence (RL) of dosimetricgrade Al2O3:C crystals is described and demonstrated in reference conditions with 12-MV photon beams from a Saturne 43 linear accelerator (LINAC), simulating External Beam Radiation Therapy (EBRT) treatments. During the course of irradiation, a portion of electrons is trapped within the Al2O3:C crystal while another portion recombines and generates RL, recorded on-line using an optical fiber. The RL sensitivity is dosedependent and increases in accordance with the concentration of trapped electrons. Once irradiation is completed, the Al2O3:C crystal is reset by laser light (reusable) and the resultant OSL (Optically Stimulated Luminescence) is also collected back by the remote RL-OSL reader and finally integrated to yield the absorbed dose. During irradiation, scintillation and Cerenkov lights generated within the optical fiber ("stem effect") are removed by a time-discrimination method involving a discriminating unit and a fiber-coupled BGO scintillator placed in the irradiation room, next to the LINAC. The RL signals were then calibrated with respect to reference dose and dose rate data using an ionization chamber (IC). The algorithm relies upon the integral of the RL and provides the accumulated dose (useful to the medical physicist) at any time during irradiation, the dose rate being derived afterwards. It is tested with both step and arbitrary dose rate profiles, manually operated from the LINAC control desk. The doses measured by RL and OSL are both compared to reference doses and deviations are about ± 2 % and ± 1 % respectively, thus demonstrating the reliability of the algorithm for arbitrary profiles and wide range of dose rates. Although the calculation was done off-line, it is amenable to realtime processing during irradiation.

Tests and Foreseen Developments of Fibered-OSLD Gamma-Heating Measurements in Low-Power Reactors

“…Another interesting feature of the fibered-OSL system is the presence of a radio-luminescence (RL) signal during the irradiations. However, in order to use this signal for dose or dose rate measurements, it would require a calibration of the RL response of the sensors with respect to dose and to dose rate [9].…”

Real-time dosimetry with Yb-doped silica optical fibres

“…This 'stem effect' can be dealt with by several methods. The main investigated approaches have consisted in trying to spectrally or temporally separate the two contributions, and in using additional reference fibres (Clift et al 2002, Beddar 2006, Guillot et al 2011, Liu et al 2011, Magne et al 2013, Veronese et al 2013a, Martinez et al 2015, Kertzscher and Beddar 2016.…”

“…Once the traps are filled by carriers, they are no longer competing with luminescent centres and scintillation efficiency reaches a maximum value. However, if the traps are not stable and release carriers in a short time interval, this effect still causes instability of the sensor, requiring signal corrections and frequent calibrations (Andersen et al 2006, Magne et al 2013.…”

Tests and foreseen developments of fibered-OSLD gamma heating measurements in low-power reactors

“…Another interesting feature of the fibered-OSL system is the presence of a radio-luminescence (RL) signal during the irradiations. However, in order to use this signal for dose or dose rate measurements, it would require a calibration of the RL response of the sensors with respect to dose and to dose rate [9].Nevertheless, some limitations appeared when using this system in EOLE. The main one was that the read-out time of the fibered sensor, from the start of the laser stimulation to the bleaching of the OSL crystal, is similar to the irradiation duration.…”