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Assessing DNA Damage Repair From CT Studies in Whole Blood

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S Elgart

SR Elgart*, A Adibi, M Khatonabadi, S Ruehm, D Enzmann, M McNitt-Gray, K Iwamoto, UCLA, Los Angeles, CA

MO-D-134-9 Monday 2:00PM - 3:50PM Room: 134

Purpose:
To assess biological damage due to radiation from CT studies using in vivo and ex vivo blood samples processed with a newly developed protocol involving flow cytometry.

Methods:
This study was carried out under IRB approval. Blood samples were collected from 21 patients undergoing clinically-indicated CT exams. Blood was procured prior to, immediately after and 30minutes following irradiation. For each patient, a sample of pre-scan blood was transferred into a vial and positioned on the patient within the scan region for ex vivo comparative analysis. Whole blood samples were fixed immediately following each collection to arrest cellular metabolism. The cellular response to DNA double strand breaks (DSBs) was analyzed by flow cytometric quantification of gammaH2AX fluorescence. Median fluorescence of treatment samples were compared to non-irradiated control blood samples for each patient.

Results:
Four patient samples were excluded due to technical issues in collection and analysis. The remaining 17 showed two major trends for gammaH2AX signal following irradiation in vivo. Some samples showed an increase immediately following irradiation and a further increase at 30minutes. Others showed an increase immediately following irradiation then a subsequent decrease at 30minutes. However, ex vivo samples showed different kinetics to in vivo counterparts. Interestingly, two patients had high basal gammaH2AX fluorescent signal (p<0.01) and exhibited large increases following irradiation. This result was apparent for both patients after in vivo analysis, but only one patient after ex vivo analysis.

Conclusion:
These results indicate significant variation in damage and repair kinetics across a small sample of patients; furthermore, we demonstrated differences between in vivo and ex vivo samples. Rapid analysis and accurate timing offer the ability to assess a large number of patients to establish baseline population data. Additionally, this method may serve as an indicator to identify patients for further analysis of radiation sensitivity.

Funding Support, Disclosures, and Conflict of Interest: Research partially supported by a grant from Siemens AG

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