Program Information
Exam and Patient Parameters Affecting the DNA Damage Response Following CT Studies
S Elgart*, A Adibi , M Bostani , S Ruehm , D Enzmann , M McNitt-Gray , K Iwamoto , UCLA School of Medicine, Los Angeles, CA
Presentations
TH-C-18A-9 Thursday 10:15AM - 12:15PM Room: 18APurpose: To identify exam and patient parameters affecting the biological response to CT studies using in vivo and ex vivo blood samples.
Methods: Blood samples were collected under IRB approval from 16 patients undergoing clinically-indicated CT exams. Blood was procured prior to, immediately after and 30minutes following irradiation. A sample of pre-exam blood was placed on the patient within the exam region for ex vivo analysis. Whole blood samples were fixed immediately following collection and stained for γH2AX to assess DNA damage response (DDR). Median fluorescence of treated samples was compared to non-irradiated control samples for each patient. Patients were characterized by observed biological kinetic response: (a) fast – phosphorylation increased by 2minutes and fell by 30minutes, (b) slow – phosphorylation continued to increase to 30minutes and (c) none – little change was observed or irradiated samples fell below controls. Total dose values were normalized to exam time for an averaged dose-rate in dose/sec for each exam. Relationships between patient biological responses and patient and exam parameters were investigated.
Results: A clearer dose response at 30minutes is observed for young patients (<61yoa; R²>0.5) compared to old patients (≥61yoa; R²<0.11). Fast responding patients were significantly younger than slow responding patients (p<0.05). Unlike in vivo samples, age did not significantly affect the patient response ex vivo. Additionally, fast responding patients received exams with significantly smaller dose-rate than slow responding patients (p<0.05).
Conclusion: Age is a significant factor in the biological response suggesting that DDR may be more rapid in a younger population and slower as the population ages. Lack of an age-related response ex vivo suggests a systemic response to radiation not present when irradiated outside the body. Dose-rate affects the biological response suggesting that patient response may be related to scan timing and dose delivery within an exam protocol.
Funding Support, Disclosures, and Conflict of Interest: All authors receive(d) funding from a Master Research Agreement from Siemens Healthcare with UCLA Radiological Sciences.
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