S1693
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
7791. doi.org/10.3390/app12157791 [2] Junis I, Yousif Y, Stensmyr R, Barber J. Comprehensive characterisation of the IBA myQA SRS for SRS and SBRT patient specific quality assurance. Phys Eng Sci Med. 2024 Mar;47(1):327-337. doi: 10.1007/s13246- 023-01370-0. Epub 2024 Jan 18. PMID: 38236315. Keywords: PSQA, Cyberknife, Gantry Angle Sensor
PRESAGE is dose-rate independent. At depths near to and shallower than Dmax there was increased uncertainty in the results due to unevenness in the phantom surface and low signal-to-noise ratio. Conclusion: PRESAGE phantoms show dose-rate independence for a wide range of ultra-high-dose-rate electron beams, indicating these phantoms can be useful for relative 3D dose measurements in FLASH electron beams. Keywords: FLASH, 3D dosimeters Digital Poster Highlight 4725 Extending TRS-483/TG-155 to Gamma Knife: Linear beam quality scaling and low-perturbation chamber orientations using Monte Carlo and experiments Tasnim Rahman 1,2 , Lalageh Mirzakhanian 3 , Robert Heaton 4,2 , Jan Seuntjens 1,2 , Catherine Coolens 1,2 1 Department of Medical Biophysics, University of Toronto, Toronto, Canada. 2 Princess Margaret Cancer Centre, University Health Network, Toronto, Canada. 3 Medical Physics Unit, McGill University, Montreal, Canada. 4 Department of Radiation Oncology, University of Toronto, Toronto, Canada
Digital Poster 4698 3D DOSIMETRY FOR ELECTRON FLASH
RADIOTHERAPY UTILIZING PRESAGE PHANTOMS WITH OPTICAL CT SCANNING AS A 3D DOSIMETRY SYSTEM Cheng-Shie Wuu 1 , Carl Elliston 1 , Mahbubur Rahman 2 , Austin Sloop 2 , Yi-Fang Wang 1 , Rongxiao Zhang 2 , John Adamovics 3 1 Radiation Oncology, Columbia University, New York, USA. 2 Thayer School of Engineering, Dartmouth College, Hanover, USA. 3 Chemistry, Rider University, Lawrenceville, USA Purpose/Objective: Radiochromic plastic dosimeter PRESAGE has been used for 3D dosimetry for many years. In this study, the feasibility of utilizing PRESAGE phantoms and an optical CT scanner for 3D dose measurements in ultra- high-dose-rate FLASH electron beams was assessed. Material/Methods: Experiments were performed using a Varian 2100 C/D linear accelerator, converted to deliver ultra-high- dose-rate 10 MeV electron beam. The LINAC delivered approximately 0.7 Gy/pulse for FLASH irradiations. Dose rate was varied from about 40 Gy/s to 240 Gy/s by changing the repetition rate. PRESAGE phantoms were irradiated en face at six FLASH dose rates: 40 Gy/s, 80 Gy/s, 120 Gy/s, 160 Gy/s, 200 Gy/s, and 240 Gy/s. EBT film and scintillator measurements were used to verify dose. Optical response of PESAGE phantom versus delivered dose was evaluated with various known doses. A novel parallel-beam optical CT scanner, utilizing fiber optic taper for collimated images, was developed for fast, high resolution, and accurate readout of 3D dosimeters. Percent depth dose curves for various FLASH dose rates and regular dose rate were generated and compared based on the optical response versus dose measurements. Percent depth dose curves from Eclipse Monte Carlo calculation were also generated. Results: The optical density of PRESAGE phantom was confirmed to be linear with absorbed dose, consistent with the observation at regular treatment dose rates. At depths past D90, percent depth dose as a function of depth for six FLASH dose rates (240-40 Gy/s) are nearly identical, indicating that optical response of
Purpose/Objective: To deliver a protocol ready set of small-field correction
factors for widely used Gamma Knife® chambers and phantom materials, and to establish a practical material-scaling rule for GK calibration. cross chamber orientations and phantoms, (ii) test, and confirm, the near linear dependence on phantom electron density, Specifically, we (i) quantify and (iii) identify chamber–orientation pairs that minimize perturbation, enabling quick interpolation for material substitutions and reduced uncertainty when implementing TRS-483/TG-155 in routine GK
calibration and QA. Material/Methods:
A Monte Carlo model of the Leksell GK Perfexion was implemented in EGSnrc [1]. The MSR field was a 16×16 mm² GK phase space; the CR field was a tabulated 60Co 10×10 cm² beam at 100 cm SSD [2]. Chambers (IBA CC01/CC04/CC13, PTW 31010/31021, Exradin A16) were simulated with manufacturer geometries and realistic electrode compositions. Phantoms included liquid water (LW), ABS, Solid Water (SW), polystyrene (PS), and PMMA. For each chamber we
computed in the parallel and perpendicular orientations (TRS-483/TG-155 conventions) [3,4], and
experimentally derived dose-to-water values
under
TG-21 and TRS-483 for comparison with expected
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