S1635
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
detector area. X-ray spectra were generated with the SpekPyTM toolkit. Copper and Tin x-ray tube filters were implemented into the simulated geometry. MC dose calculations were performed for intracranial and lung CKRS applications, on digitized patient models reconstructed by corresponding treatment planning CT images. The absorbed dose to eye lenses (intracranial cases) and skin (lung cases) were calculated for variable copper and tin (lung cases only) filters with thicknesses ranging from 0.1 mm to 1 mm. Dosimetry results were normalized to the same signal in the central 2×2 cm² detector region, which required an increase in the tube current–time product (mAs) with increasing filter thickness. Results: Imaging doses of up to 7 cGy per 100 image acquisition pairs were found at 120 kV/10 mAs tube loading for the bone medium, due to its higher mass energy-absorption coefficient in this energy range (Figure). The mean absorbed dose to the eye lenses was 6 cGy per 100 image acquisition pairs. Implementation of copper filters reduced the imaging dose to eye lenses by 29 – 60% for filter thicknesses of 0.1 – 1.0 mm, respectively. The corresponding increase in mAs ranged from 12% to 152%, rendering the 0.1 mm copper thickness the most efficient choice. Regarding the maximum dose to skin, it was most efficiently reduced using 0.1 mm copper, since a dose reduction of 21% came at the expense of only 11% increase in tube load (Figure). Tin filters achieved 34– 67% reductions in maximum skin dose but required substantially higher mAs (37–648%).
Conclusion: The optimal solution depends on the dose-per-pulse regime and requires a balance between measurement accuracy and sensitivity when choosing between samples (1) and (3). In addition, the sensitivity still needs to be improved, for instance, through cavity- enhanced absorption spectroscopy. References: [1] J. Megroureche, H. Bekerat, J. Bian, A. Bui, J. Sankey, L. Childress, and S. A. Enger, Development of a hydrated electron dosimeter for radiotherapy applications: a proof of concept, Medical Physics 50, 7245–7251 (2023)[2] E. J. Hart and E. M. Fielden, The hydrated electron dosimeter, book section Procedures in Radiation Dosimetry: Liquid Chemical systems, pages 331–335, Marcel Dekker, New York, 1970[3] E. M. Fielden and E. J. Hart, Primary Radical Yields in Pulse-Irradiated Alkaline Aqueous Solution, Radiation Research 32, 564–580 (1967) Keywords: radiation chemistry, detector response Digital Poster Highlight 1156 Revisiting X-ray tube filtration for optimizing imaging dose in robotic radiosurgery Panagiotis Archontakis 1,2 , Argyris Moutsatsos 2 , Anastasia Stergioula 2 , Evaggelos Pantelis 1,2 1 Medical Physics Lab, Medical School, National and Kapodistrian University of Athens, Athens, Greece. 2 Radiotherapy Department, Iatropolis Clinic, Athens, Greece
Purpose/Objective: In CyberKnifeTM (Accuray Inc., USA) robotic
radiosurgery (CKRS), accurate and precise registration of the planned dose distribution to target anatomy is facilitated by kilovoltage (kV) x-ray based image guidance. This study used Monte Carlo (MC) simulations to explore the potential for reducing patient imaging dose through the implementation of additional x-ray tube filtration. Material/Methods: The CyberKnife target locating subsystem (TLS) was modelled using the EGSnrc MC toolkit. The TLS consists of two ceiling-mounted x-ray tubes (40–150 kV, 25-300 mA, 1-500 ms) and two in-floor amorphous- silicon flat-panel detectors. The imaging field at isocenter is confined to 17×17 cm² by trapezoidal collimators, corresponding to a 41×41 cm² active
Conclusion: Additional x-ray tube filtration can effectively reduce
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