Comparison of Radiation-Induced DNA Damage between Conventional and Computed Tomography Coronary Angiography

Gökhan Gökalp (  gokhangokalp23@hotmail.com ) Gazi University Faculty of Medicine: Gazi Universitesi Tip Fakultesi https://orcid.org/0000-0002-49587266 Serkan Ünlü Gazi University Faculty of Medicine: Gazi Universitesi Tip Fakultesi Aylin Elkama Gazi University: Gazi Universitesi Alican Yalçın Gazi University Faculty of Medicine: Gazi Universitesi Tip Fakultesi Mustafa Cemri Gazi University Faculty of Medicine: Gazi Universitesi Tip Fakultesi Bensu Karahalil Gazi University Faculty of Medicine: Gazi Universitesi Tip Fakultesi Gonca Erbaş Gazi University Faculty of Medicine: Gazi Universitesi Tip Fakultesi Nuri Bülent Boyacı Gazi University Faculty of Medicine: Gazi Universitesi Tip Fakultesi


Introduction
Coronary artery disease (CAD) is the leading cause of morbidity and mortality in the world with an increasing prevalence regardless of the development status of the countries (1, 2). Although different modalities have been proposed for the diagnosis of coronary artery disease, conventional coronary angiography (CCA) and coronary computed tomography angiography (CCTA) are the tools commonly used for the diagnosis of CAD (3). CCA remains as the gold standard method for the diagnosis due to its high spatial and temporal resolution. However, it has several disadvantages such as need for hospitalization, risk of complications and high cost (4,5). However, CCTA is a noninvasive alternative, especially in the population with low and moderate risk of CAD (6,7). Recently novel developments in CCTA made it available to provide better anatomical details of coronary arteries by leading to useful information for the diagnosis of CAD (8,9). The commonality of both imaging methods is using ionizing radiation, which could have mutagenous effects (5,10). The radiation dose, which was previously reported to be higher in CCTA than CCA, decreased signi cantly with dual-energy technology (11). Using the ash technique an option presented in devices with recent technology, has also reduced the radiation dose to its minimum (11)(12)(13).
Ionizing radiation has many somatic and genetic effects on tissues. The increase in cancer risk, which is the most feared effect, has previously been demonstrated in observational studies, especially in people exposed to radiation (14). The most important factor is DNA damage for the risk of cancer due to radiation exposure. There are several methods for detecting radiation-induced genotoxic damage.
Chromosome aberration test (CAT) is a standard method commonly used to detect various structural chromosomal abnormalities induced by mutagens (15)(16)(17).
Thus, we sought to compare ionizing radiation doses of CCA and CCTA and radiation-induced DNA damage by chromosome aberration test caused by these imaging techniques.

Study Population
A total of 76 patients over 18 years, followed in XXX Cardiology Department and Radiology Departments were included. Thirty-nine patients underwent CCA and 37 patients underwent CCTA for diagnosis of CAD.
Patients who had a history of malignancy, chemo-radiotherapy, coronary artery anomaly and radiological procedures other than chest radiography in the last year and patients with signs of active infection were excluded. In addition, since we aimed to compare CCTA with diagnostic CCA, patients who were performed ventriculography percutaneous coronary intervention in the same session were excluded.
Before their participation, patients were informed about the research and written consents were obtained. This study was approved by the local ethical committee (XXX Faculty of Medicine Clinical Research Ethics Committee on 11.09.2017).

Study Protocol
Patients who were perfomed CCTA were divided into two groups according to being scanned with prospective ECG-triggered high-pitch spiral technique with dual-energy CT device (CT-ash). Thus, three patient groups were formed at last; CCA, CCTA-ash and CCTA-other. Baseline characteristics and effective radiation doses obtained from imaging tools were calculated and recorded. Blood samples were taken immediately before and one hour after imaging protocol.

Conventional Coronary Angiography
Conventional coronary angiography procedures were performed on the Innova IGS 320, General Electric Healthcare (Milwaukee, USA) device by physicians experienced in interventional cardiology. The number of images was left to the initiative of the interventional cardiologist, provided that all coronary imaging were performed (Figure 1).
Coronary Computer Tomography Angiograph 384 sections (192x2), dual energy, 3 rd generation tomography device Somatom Force CT, Siemens Healthcare (Siemens AG, Erlangen, Germany) was used for CCTA. All patients had coronary calcium scoring before angiography procedure. No negative chronotropic agents were given to patients to reduce pre-procedure pulse. The imaging protocol was determined by the radiologist according to the pulse rate of the patients during the procedure (Figure 2). Flash mode shooting (prospective ECG-triggered highpitch spiral technique with dual-energy) was performed for eligible patients.

Radiation Dose Measurements
There are different parameters to calculate the radiation doses of the patients. In our study, we used the effective dose (ED) which is more frequently used among these parameters. The dose-area product (DAP) values of the patients who underwent CCA automatically measured by the device after the procedure and were converted to ED unit (mSv) by multiplying the converting factor for diagnostic CCA by 0.12 mSv / Gy.cm 2 . In CCTA, the dose-length product (DLP) values given by the device were converted to ED by multiplying the conversion factor 0.014 mSv x (mGy x cm) -1 for the chest region.

Chromosome Aberration Test
CAT is a standard method commonly used to detect various structural and numerical chromosomal abnormalities induced by mutagens. Chromosome aberration frequency determined in circulating lymphocytes is a biomarker of cancer risk and re ects both early biological effects and individual sensitivity of exposure to genotoxic carcinogens (17). Chromosomal aberration analysis of human lymphocytes on metaphase is still accepted as the gold standard method for radiation biodosimeter (18). In our study, standard procedures were applied to the blood samples taken from patients before and after the imaging procedures for CAT. After lymphocytes were kept at the metaphase stage and spread to the slides, 100 metaphases were examined by experienced researchers for each individual (Figure 3). In our study, the structural aberration types, chromosome-chromatid gap, chromosome-chromatid fracture, ring chromosome, dicentric and asentric chromosomes were determined and total aberration rate was calculated before and after procedure for each patient. The relative change in chromosome aberration rates was accepted as the genotoxic effect of radiation.

Statistical Analysis
Statistical analyzes were performed using IBM SPSS (IBM, Chicago, IL, USA) for Windows Version 19.0 package program. Numerical variables were summarized with mean ± standard deviation or median [interquartile range]. Categorical variables were represented by numbers and percentages. The normality of numerical variables was examined by Shapiro Wilks test. The difference between the numerical values before and after imaging was examined by using T test in dependent groups in case of parametric test assumptions and Wilcoxon test in case of lack of parametric test assumptions. Differences between categorical variables were evaluated by chi-square test. Differences between groups were analyzed by one-way analysis of variance if parametric test assumptions were met, and Kruskal Walli's test if parametric test assumptions were not met. Bonferroni correction was applied for post-hoc tests. Changes in the parameters of genetic damage assessment before and after imaging were calculated as a percentage. Signi cance level was accepted as p <0.05.

Results
Totally 76 patients were included in the study and CCA group consisted of 39 patients. The patients who underwent CCTA were divided into two groups according to the ash mode of the device. Of the 37 patients who underwent CCTA, 22 (59.5%) were in the CCTA-ash group and 15 (40.5%) were in the CCTAother group. The baseline demographic and clinical characteristics of the participants are shown in Table  1. The mean age of the patients was 56.9 ± 10.8 years. Basal characteristics of the groups were similar except heart rate and age. The mean age of the CCTA-other group was higher compared to others.
The mean effective radiation dose given to all participants was 4.6 ± 2.9 mSv. The mean dose of radiation administered was signi cantly different between the groups (Figure 4). The highest radiation was observed in the CCTA-other group with an ED of 7.2 ± 2.4 mSv. The least radiation was seen in the CCTA-ash technique and the mean ED was 1.1 ± 0.2 mSv.
Total chromosome aberration rates measured by CAT before and after imaging methods are shown in Table 2. In the CCTA-ash group with the lowest radiation dose, there was no change in chromosome aberration rate after the study. Chromosome aberration rates increased signi cantly after imaging protocols for patients in the CCA and CCTA-other groups. The increase in these two groups was found to be similar (p = 0.366).

Discussion
In our study; we aimed to compare genotoxic damage due to ionizing radiation by assessing CAT in patients who underwent CCA and CCTA. Radiation dose was signi cantly lower in CCTA-ash group compared to other groups. While chromosomal aberration rate was not increased for CCTA-Flash group, chromosome aberrations were observed in CCTA-Other and CCA groups.
Coronary artery disease is one of the most important health problems worldwide due to its negative consequences and frequency (1,2,19). Although CCA still appears to be the gold standard in diagnosis; use of CCTA has increased considerably with the latest technological advances (10,20). There are two important reasons for this increase: rstly it provides very good anatomical detail in the visualization of coronary arteries with the increase in the number of sections with three-dimensional isometric imaging feature (8,9). Secondly high radiation doses previously feared in CT have been reduced by techniques in the new generation CT devices (11,21,34). The number of patients being scanned by CCA or CCTA is increasing due to higher admissions to hospitals with increased sensitivity to CAD. Moreover, access to mentioned imaging tools has become easier. This makes it more necessary to know the effects of ionizing radiation used in imaging method. Current guidelines emphasize that CCTA should be preferred for the diagnosis of CAD (22). However, adequate protocols should be followed to achiveve low radiation doses to prevent radiation-induced comorbidities.
Radiation doses in CCA and CCTA have been compared many times and previous studies observed that patients are exposed to more radiation in CCTA (23,24). However, with the development of CT technology, especially with the emergence of dual energy CT systems, the radiation dose decreased in CCTA scans (25). Flash mode in dual-energy CCTA devices transmits low dose in a single pulse during a certain period of the cardiac cycle (12,13,26). In our study, it was observed that the patients had very low dose of radiation, such as 1.1 ± 0.2 mSv, on ash mode. This result was found to be consistent with previous studies (12,27,33). In order to use ash mode in dual-energy CT devices, patients' heart rates should be low (28,29). Therefore, in our study, it is expected that the heart rates of patients with CCTA-ash group are lower than the other groups. The average ED calculated in the CCA group was found to be similar to previous studies (29).
Genotoxicity of ionizing radiation in CCTA has been shown in several studies (30,31). However, there is a few studies comparing CCA and CCTA in this respect (5). Our study provided clinically important results by comparing two methods that expose radiation and whose prevalence is increasing day by day. Chromosomal damage has an important role as a biological indicator of genotoxic carcinogen exposure such as ionizing radiation. Determining the frequency of chromosomal aberration in cultured peripheral blood lymphocytes is one of the most widely used methods in evaluating the biological effects of genotoxic carcinogen exposure (32). In our study, we preferred the CAT because it shows genotoxicity effectively by being reliable for many years. There is no study comparing dual-energy CCTA and CCA using the CAT for the genotoxic effects of radiation.
Our results revealed that chromosome aberration increase was lowest in the CCTA-ash group, which has a signi cantly lower mean radiation dose received. However, the increase in chromosome aberration rate was not higher in CCTA-other group which has the the highest mean radiation dose received compared to CCA group (p = 0.366). It could be explained that the number of patients is not enough to provide a statistically signi cant difference and genotoxic effect may depend not only on radiation dose but also on individual sensitivity. Therefore larger prospective studies should be performed.

Limitations of the Study
The most important limitation of our study was the limited number of patients, however, we believe to explicit relevant results. Another limitation is that evaluation of chromosome aberration can be subjective. Therefore, it was evaluated by the only experienced researchers.
The results of this study indicate that coronary imaging with CCTA-ash mode in dual -produces less radiation and radiation-induced genotoxicity than non-ash mode CT scans and CCA. Further studies with a larger patient population are necessary to con rm the results of our study.

Main Points
Coronary computed tomography angiography with ash mode in dual energy devices produces less radiation Coronary computed tomography angiography with ash mode in dual energy devices results less radiation induced genotoxicity assessed by chromosome aberration.

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Conventional coronary anjiography and coronary computed tomography angiography with non-ash mode result similar radiation-induced genotoxicity assessed by chromosome aberration.

Declarations
Funding Not applicable Con icts of interest/Competing interests All authors report no relationships that could be construed as a con ict of interest.

Ethics approval
The study was approved by the Gazi University Faculty of Medicine ethics committee.

Consent to participate
All subjects gave written informed consent prior to inclusion   Figure 1 Conventional coronary angiography image of a study patient.

Figure 2
Coronary computed tomography angiography image of a study patient.

Figure 3
Chromosome aberration test of lymphocyte chromosomes at the metaphase stage with light microscopy.