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Session: Therapy BLUE RIBBON [Return to Session]

To Establish Correlation Between Physical Microdosimetric Quantities Such as Dose Mean Lineal Energy, Target Size and Biological Endpoints Such as DNA Double Strand Breaks in HeLa Cells Irradiated with Iridium-192 High Dose Rate Brachytherapy Source and 225kV X-Rays

S Dev1*, B Behmand2, P Pater3, S Abbasinejad Enger4, (1) McGill University, Montreal, QC, CA, (2) University of McGill, Montreal, QC, CA, (3) McGill University Health Centre, Montreal, QC, CA, (4) Lady Davis Institute for Medical Research, Jewish General Hospital, Montreal, QC, CA


MO-I430-BReP-F3-5 (Monday, 7/11/2022) 4:30 PM - 5:30 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: To establish correlation between physical microdosimetric quantities such as dose mean lineal energy, target size and biological endpoints such as DNA double strand breaks in HeLa cells irradiated with Iridium-192 high dose rate brachytherapy source and 225 kV x-rays.

Methods: Nuclei size distributions and γ-H2AX foci were extracted from previously obtained fluorescent microscopy images for HeLa cell line irradiated with Iridium-192 and 225 kV x-rays to an absorbed dose of 4 Gy. Then, the nuclei and cell radii distributions were extracted using a Watershed algorithm implemented in Scikit-Image, and the dose mean lineal energies, yd, were calculated using MicroDose (in-house Monte Carlo code for microdosimetry applications based on Geant4) and the Large-scale Atomic/Molecular Massively Parallel Simulator for both radiation qualities for fixed radii distributions (5-20 μm) and the ones extracted from our microscopy slides.

Results: After irradiation of HeLa cells with Iridium-192, the measured mean cell nuclei radius was lower by 0.91 than when irradiated with 225 kV x-rays. The mean number of γ-H2AX foci per nuclei after Iridium-192 irradiations were lower by 0.66 compared with after 225 kV x-rays irradiations. For target sizes ranging from 5.0 μm to 20.0 μm, the y values range from 1.132 +/- 0.090 keV/μm to 0.757 +/- 0.018 keV/μm for Iridium-192 and 1.625 +/- 0.022 keV/μm to 0.759 +/- 0.010 keV/μm for 225 kV x-rays. A higher correlation coefficient between yd and number of γ-H2AX foci per nuclei was obtained for Iridium-192 (R²=0.616) as compared to 225kV x-rays (R²=0.4826).

Conclusion: The yd values increase with decreasing target size for both radiation qualities investigated. The dose mean lineal energy calculated for individual HeLa cell nuclei present in microscopy samples is strongly correlated with the number of γ-H2AX foci per nuclei induced after Iridium-192 irradiations than after 225 kV x-rays irradiations.

Funding Support, Disclosures, and Conflict of Interest: Funded by: MEDTEQ+ the PSOv2b program, cofounded with TransMedTech, Mitacs, the MUHC Foundation and Alpha Tau Medical. Computations were performed on the Niagara supercomputer at the SciNet HPC Consortium of Calcul Quebec.


Microdosimetry, Radiobiology, X Rays


TH- Radiobiology(RBio)/Biology(Bio): RBio- Photons

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