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.

X-ray sources are widely used in medicine: brachytherapy, radiodiagnosis, mammography and contact radiotherapy. Kerma in air is the primary quantity measured to determine the dose to the patient. Accurate air kerma assessment is obtained using correction factors calculated using the emission spectrum. The Laboratoire National Henri Becquerel launched an in-depth study of the spectral emission of its reference X-ray beams used in dosimetry. Two semiconductor detectors are discussed here: a High-Purity germanium and a silicon PiN, both cooled and operated with dedicated electronics and software. In the low energy range (E < 50 keV), those spectrometers are complementary but require a careful calibration to deduce the emitted spectrum from the detected one. Indeed, both detectors were characterized in terms of spectral response and intrinsic efficiency using a tuneable monochromatic X-ray source (SOLEX at CEA Saclay) in the 5-to 20-keV energy range and various radionuclides. The characterization methods and results, including the first measured spectra of medical X-ray tubes (high voltage < 50 kV), are presented in this work. This paper presents the first step of a broader project, aiming at assessing the emission spectrum independently of the detector choice.

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