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Correlation Between Radiation-Induced Foci and Tumor Nuclei Size Distribution

B Behmand1*, Y Kamio1, M Evans2, S Abbasinejad Enger3, (1) Medical Physics Unit, McGill University, Montreal, QC, CA, (2) McGill University Health Centre, Montreal, QC, CA, (3) Department of Oncology, McGill University, Montreal, QC, CA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: DNA is the most important target in radiotherapy. Generally, the DNA lesions are determined by an average over all the exposed cells. However, there is a variation in cell/nuclei size for the same cell type and also between different cancer cells. Due to the stochastic nature of radiation, there is a fluctuation in number of tracks traversing and depositing energy in each cell, which depends on the radiation quality and the size of the cell. Phosphorylation of H2AX protein at the site of DNA double strand break (DSB) a few minutes following radiation induces ?-H2AX foci and can be used as a biomarker for DSBs. In this study, variation in induction of DSBs based on nuclei size distribution in different cancer cell lines irradiated with different radiation qualities was investigated.

Methods: Prostate PC-3, cervix HeLa adenocarcinoma and breast cancer MDA-MB 231 cells were irradiated with microSelectronV2 ¹?²Ir brachytherapy source and X-RAD SmART 225 kV. Prior to radiation, cells were seeded in 4-well chamber slides or 60 mm petri dishes to ~80% confluency and synchronized overnight in G0/G1 by serum starvation. The cells were exposed to 1, 2 and 4 Gy. The expression of ?-H2AX and nuclei region were evaluated by immunofluorescence analysis with the post irradiation time of 30 min or 1h. Fluorescent labeled cells were quantified with confocal microscopy and imaging flow cytometry.

Results: The dosimetric validation of the ¹?²Ir irradiation setup was done using EBT3 Gafchromic films. The results show that the number of foci increases linearly with the nuclei size for three investigated cancer cell lines for both ¹?²Ir and kV x-rays. Furthermore, the number of ?-H2AX foci following ¹?²Ir radiation is slightly higher when compared to the x-rays.

Conclusion: The preliminary results show a correlation between the number of DSB and nucleus size following radiation.

Funding Support, Disclosures, and Conflict of Interest: This research was conducted as part of the activities of the TransMedTech Institute, thanks in part to the financial support of the Fonds de recherche du Quebec.


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