L. de Carlan

Multichannel dosimeter and α-Al 2 O 3 :C Optically Stimulated Luminescence (OSL) fiber sensors for use in Radiation Therapy - evaluation with photon beams

A multichannel OSL Fibre Optic dosimeter based on Optically Stimulated Luminescence (OSL) of alumina is proposed for on-line In Vivo Dosimetry (IVD) in Radiation Therapy (RT). Two types of dosimetric-grade Al2O3:C crystals are compared and show different behavior according to manufacturing process. Metrological validations have been performed with a Saturne 43 LINAC in reference conditions at CEA LIST LNHB (French Ionizing Radiation Reference Laboratory). The dose response of OSL integrals under photon beam irradiation (6, 12 and 20 MV) show sublinearity behavior modeled by second-order equations and exhibit a small energy dependence (between 0.7% and 1.4%), explained by a modified intermediate cavity model adapted to a LINAC photon spectrum. Preclinical tests at Institut Gustave Roussy (IGR) prove that a proper design for a PMMA build-up cap leads to a low dependence vs photon beam orientation (± 1.5 % and ± 0.9 %) and vs field size in view of surface measurements.

Intracavitary in vivo dosimetry based on multichannel fiber-coupled Radioluminescence and Optically Stimulated Luminescence of Al 2 O 3 :C

Fiber Optic Dosimetric Catheters (FODCs) composed of chains of alumina crystals are investigated by the CEA LIST within the French ANR-INTRADOSE Project in the purpose of intracavitary in vivo dosimetry (IVD) during Brachytherapy (BT) with iridium sources and Intensity-Modulated Radiation Therapy (IMRT) with linear accelerators. A dedicated process involving PMMA fibers, casted altogether forming hexagonal bundle, is demonstrated. Optically Stimulated Luminescence (OSL) signals are recorded on-line after irradiation and absorbed doses are compared to planned dose distribution. Real-time dose measurements may also be performed by recording the RadioLuminescence (RL), spontaneously emitted by the crystals during irradiation. In this case, a correction method is implemented to correct for stem effect influence (Cerenkov and scintillation generated within the fibers). For BT, the dual-fiber subtraction method is used (using a reference fiber) whereas the time discrimination method is used for IMRT. The experimental dose distribution leads to an underestimation of the source-sensor distance presumably due to energy dependence of the alumina crystal at low photon energy. At the time being, Monte-Carlo modeling of the FODC is performed with the aim to estimate this energy dependence and finally correct for it. Finally, metrological and preclinical validations are still running at Centre Léon Bérard (Lyon, France) in the purpose of checking the compliance of the FODC prototypes with treatment specifications and medical constraints.