S1670
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
Université Toulouse 3-ERL5294 CNRS, Oncopole, Toulouse, France. 3 Observatoire Midi Pyrénées, UAR831, Université de Toulouse, CNRS, IRD, Toulouse, France. 4 LEGOS, UMR5566, CNRS, IRD, Toulouse, France. 5 Radiation Protection, Univ Toulouse, Oncopole Claudius Regaud, IUCT-Oncopole, Toulouse, France Purpose/Objective: The periodic renewal of linear accelerators (linac) used in radiotherapy, whose number is increasing, raises the issue of managing their activated internal components. During operation, materials exposed to particle fluxes become radioactive. The management of these activated wastes requires accurate radiological characterization, which remains yet delicate to achieve. Hence, the lack of characterization methodology leads treatment centres to keep their activated components on site, leading to long-term storage of important waste amounts.This study aims at developping a radiological characterization method to identify and quantify activities of gamma-emitting radionuclides in activated linac components. Material/Methods: Two activated components from the head of a Clinac IX linac (Varian Medical Systems), taken downstream of the monitor unit ionization chamber, were investigated. The linac operated between 2011 and 2023, delivering high-energy photons (6 and 18 MV) and electrons (6 MeV to 15 MeV) for a total of 5,800 hours. Treatments were mainly delivered using volumetric modulated arc therapy with 6 MV photon beams.Measurements by X-ray fluorescence were performed to compare with theoretical chemical compositions. Each component was sampled at different depths and locations and was analyzed by gamma spectrometry, resulting in a 3D map of activity. Potential activation reactions were also studied using nuclear data from NuDat 3.0 and the Java-based nuclear information software (JANIS). This approach allowed tracing the expected activation reactions and radionuclides, which could be compared to the radionuclides determined using gamma spectrometry. Results: Chemical composition of the components were found consistent with the manufacturer’s data (i.e., W(0.85), Ni(0.12) and Cu(0.03)), but also revealed the presence of impurities (i.e., Fe, S, Co, Mn and Mo), which together accounted for 1.11 wt% of the total composition. Six radionuclides were identified: 54Mn, 57Co, 58Co, 60Co, 179Ta and 181W, with activities ranging from 7.10-2 to 5.101 Bq/g (Figure 1) depending on the radionuclide and the sampling location within the material. The presence of impurities in the components led to excess activity of certain radionuclides, such as 54Mn. Activity profiles as a function of depth in the component generally show an
For hypofractionated treatments (10 – 20 Gy), scan-to- scan variability contributes <1% and intrascan variability contributes <3% to overall film dose uncertainty. However, intrascan variability can be optimised with film placement or scanner response
corrections. Conclusion:
Interscan and intrascan variability were measured and propagated to dose uncertainty applying a method for independent evaluation and dose-based optimisation of film scanning. References: Marroquin EY, Herrera González JA, Camacho López MA, Barajas JE, García-Garduño OA. Evaluation of the uncertainty in an EBT3 film dosimetry system utilizing net optical density. J Appl Clin Med Phys. 2016 Sep 8;17(5):466-481. doi: 10.1120/jacmp.v17i5.6262. PMID: 27685125; PMCID: PMC5874103. Keywords: Uncertainty, film dosimetry, flat-bed scanner Digital Poster 3701 Radiological characterization of activated components from linear particle accelerators used in radiotherapy Esther Boiron 1,2 , Thomas Zambardi 3,4 , Bertrand Delpuech 5 , Pieter Van Beek 3,4 , Marc Souhaut 3,4 , Laure Vieillevigne 1,2 1 Medical Physics Department, Univ Toulouse, Oncopole Claudius Regaud, IUCT-Oncopole, Toulouse, France. 2 RADOPT, Centre de Recherches en Cancérologie de Toulouse, UMR1037 INSERM-
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