Abstract Body: Background: As medical imaging has continuously grown, patient exposure to ionizing radiation and the risks associated with it are important issues. Myocardial perfusion single-photon emission computed tomography (MP-SPECT) is one of the most frequently performed noninvasive cardiac imaging tests, generating concern about the potentially excessive radiation exposure for patients, including the cumulative doses of lifetime radiation. even though the individual levels of radiation exposure are considered low.
Aim: To evaluate DNA damage and DNA repair markers after MP-SPECT.
Methods: Thirty-two patients undergoing Tc-99m sestamibi MP-SPECT (mean injected Tc-99m sestamibi dose: 15.1 mCi) were studied. Peripheral blood was collected before radiotracer injection at rest and 60-90 minutes after injection. The comet assay (single-cell gel electrophoresis) was performed with blood lymphocytes to detect DNA strand breaks, which appear as DNA fragmentation (the comet tail; Figure1). Images of fluorescence microscopy were analyzed using the Comet Assay Software Project Lab (CASPLab 1.2.3 beta 2). Three parameters were evaluated: the percentage of DNA in the comet tail, tail length, and tail moment (the measure of migratory DNA and number of fragments). Quantitative PCR (qPCR) was performed to evaluate the expression of five genes related to signaling pathways in response to DNA damage and repair (ATM, ATR, BRCA1, CDKN1A, XPC). Data are expressed as medians, and Wilcoxon or Mann-Whitney tests were employed for statistical analysis. A p-value <0.05 was considered statistically significant.
Results: Figure 2 shows pre- and post- radiation exposure comet assay parameters. After radiotracer injection, there was a 10.7% increase of the DNA percentage in the tail (pre-exposure median 2.185 vs post-exposure median 2.418, p<0.0065). Tail length increased 6.7% (15.0 pre-exposure vs 16.0 post-exposure, p<0.0034). Tail moment increased 27.5% (0.3177 pre-exposure vs 0.4050 post-exposure, p<0.0001). qPCR did not reveal increased expression of any gene after radiation exposure.
Conclusion: An increase in DNA damage was detected after a single radiotracer injection for MP-SPECT, yet unaccompanied by activation of repair genes. This may suggest that DNA damage is not large enough to trigger intense repair responses and might not result in biologically significant DNA damage.