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ESTIMATION OF DIAGNOSTIC REFERENCE LEVELS FOR CT CORONAROGRAPHY IN SLOVAKIA

ESTIMATION OF DIAGNOSTIC REFERENCE LEVELS FOR CT CORONAROGRAPHY IN SLOVAKIA Abstract The coronary CT angiography (CCTA) is a frequent diagnostic method connected with large variability of effective dose. Therefore, it is the type of examination where optimization is very important and the use of a national diagnostic reference level (DRL) recommended. In Slovakia the DRL for interventional radiology examinations until now fails. The objective of our study was to propose the national DRL for CCTA examinations in Slovak Republic, on the basis of a cross-sectional multicenter study, performed in four departments of radiology. The study was realized in 2014–16 in a sample of 1725 patients undergoing CCTA examination. The proposed DRL expressed by CTDIVOL is 45 mGy and of DLP is 510 mGy cm. Over the last 10 years, the number of CT devices that are used in the Slovak Republic has increased by more than 43% and this leads to an increase in the number of CT examinations performed, representing nowadays ~135 examinations per 1000 inhabitants in Slovak Republic per year(1, 2). More frequent use of computer tomography is manifested in most medical disciplines, including cardiology. One of the newest diagnostic imaging methods in cardiology is the coronary CT angiography (CCTA). The rapid technological development and introduction of the CCTA into practice has led to cause questions in the scientific sphere about whether this diagnostic method is suitable as an alternative for invasive coronarography(3). These questions and uncertainties lead to the inception of many scientific studies whose primary objective was to compare invasive and non-invasive coronarography(4–7). The main argument against CCTA was the excessive use of x-rays. Earlier studies have noted that an effective dose of CCTA was higher than 20 mSv, which corresponded with ~7-year exposure from natural radiation(8). Since then, significant progress has been made and new methodologies have been developed which could reduce the effective dose by more than 50%(9). In addition to the process of introducing new methodologies and adjusting the physical parameters of examination, the Slovak national DRLs have been proposed. The DRL for CCTA is formulated by the values of volume CT dose index (CTDIVOL) and the dose–length product (DLP). CCTA is increasingly frequent diagnostic method, so a national value of DRL for CCTA is appropriate in the Slovak Republic. The objective of our study was to prepare a draft of national DRL for the Slovak Republic for the examination of the heart by CCTA. Our study is the first study in Slovakia which proposes DRL values for CT angiography protocols in this country. METHODOLOGY We performed a cross-sectional multicentre study in the Slovak Republic, with participation of four departments of radiology performing CCTA. This number of departments covers 70% of all departments of radiology in the Slovak Republic, which perform CCTA examinations. The participating departments of radiology were marked with characters A, B, C and D. The CCTA were performed according to the individual status of patient with a prospective method of ECG-gating (PT CCTA) or with a retrospective ECG-gating (RG CCTA). This study included 1725 patients, of which were 931 females and 794 males. Each patient had received the Topogram, the Coronary Artery Calcium Score and the CCTA. Exposure parameters for the study were obtained from the hospital archiving system. For statistical analysis we used the statistical software R-Project version 2.11.1 and Microsoft Office Excel 2007. For the objective of creating national DRLs we established the 75th percentile of dose distribution (CTDIVOL and DLP). The effective dose was calculate by converting DLP with k-factors from European Commission 0.017 mSv/(mGy cm). Basic characteristics were used for calculation of mean, median, minimum and maximum values, for 75th percentile and for standard deviation. Correlation and regression were used for data analysis and statistical test: Kolmogorov–Smirnov test, Wilcoxon test, T-test, Anova test and Kruskal–Wallis test. Statistical significance was set at a value lower than 0.05 (p < 0.05). The study was approved by the ethics committee and was carried out in accordance with the law on the protection of personal dates of patients. RESULTS In the study were 1725 patients (54% of females and 46% of males). Patients in the study were from 13 to 89 years old. The mean age of patients in the study was 61 years. The mean age of females was 63 years, with females from 50 to 79 years accounting 88% of all females. The mean age of males was 59 years, with males from 50 to 79 years accounting 76% of all males. The mean BMI of patients in the study was 29 kg/m2, with 75% of patients in the study having BMI of up to 32 kg/m2. Healthy BMI (20–25 kg/m2) was observed in only 22% of all patients and up to 36% of patients had obesity. The description of the personal characteristics of the patients involved in the study is in Table 1. Table 2 shows the specific numbers and characteristics of patients of individual departments of the study. Table 1. Basic characteristics of the file in the study. Gender Number Age BMI (kg/m2) Males 46% (N = 794) 59 ± 12 30 ± 5 Females 54% (N = 931) 63 ± 11 29 ± 6 Both 100% (N = 1725) 61 ± 12 29 ± 5 Gender Number Age BMI (kg/m2) Males 46% (N = 794) 59 ± 12 30 ± 5 Females 54% (N = 931) 63 ± 11 29 ± 6 Both 100% (N = 1725) 61 ± 12 29 ± 5 Table 1. Basic characteristics of the file in the study. Gender Number Age BMI (kg/m2) Males 46% (N = 794) 59 ± 12 30 ± 5 Females 54% (N = 931) 63 ± 11 29 ± 6 Both 100% (N = 1725) 61 ± 12 29 ± 5 Gender Number Age BMI (kg/m2) Males 46% (N = 794) 59 ± 12 30 ± 5 Females 54% (N = 931) 63 ± 11 29 ± 6 Both 100% (N = 1725) 61 ± 12 29 ± 5 Table 2. Basic characteristics of patients of individual departments in the study. Department Number Age BMI (kg/m2) A 66% (N = 1136) 61 ± 11 29 ± 5 B 11% (N = 194) 62 ± 10 34 ± 6 C 12% (N = 203) 65 ± 10 32 ± 5 D 11% (N = 192) 59 ± 12 — Department Number Age BMI (kg/m2) A 66% (N = 1136) 61 ± 11 29 ± 5 B 11% (N = 194) 62 ± 10 34 ± 6 C 12% (N = 203) 65 ± 10 32 ± 5 D 11% (N = 192) 59 ± 12 — Table 2. Basic characteristics of patients of individual departments in the study. Department Number Age BMI (kg/m2) A 66% (N = 1136) 61 ± 11 29 ± 5 B 11% (N = 194) 62 ± 10 34 ± 6 C 12% (N = 203) 65 ± 10 32 ± 5 D 11% (N = 192) 59 ± 12 — Department Number Age BMI (kg/m2) A 66% (N = 1136) 61 ± 11 29 ± 5 B 11% (N = 194) 62 ± 10 34 ± 6 C 12% (N = 203) 65 ± 10 32 ± 5 D 11% (N = 192) 59 ± 12 — Examinations of CCTA were performed mostly at a voltage of 120 kV and using an automatic system for adjusting exposure parameters. The most important parameters for the DRL of CCTA are CTDIVOL and DLP. Figure 1 shows the distribution of CTDIVOL and DLP of exposed patients, Figure 2 presents values of CTDIVOL and DLP of patients by gender. Figure 1. View largeDownload slide Frequency of CTDIVOL and DLP of file in the study. (A) Frequency of DLP of patients. (B) Frequency of CTDIVOL of patients. Figure 1. View largeDownload slide Frequency of CTDIVOL and DLP of file in the study. (A) Frequency of DLP of patients. (B) Frequency of CTDIVOL of patients. Figure 2. View largeDownload slide Values of CTDIVOL and DLP of file in the study. (A) Values of DLP of patients. (B) Values of CTDIVOL of patients. Figure 2. View largeDownload slide Values of CTDIVOL and DLP of file in the study. (A) Values of DLP of patients. (B) Values of CTDIVOL of patients. The CTDIVOL of all patients was ranged from 7.47 to 272.00 mGy. The 75th percentile of CTDIVOL was 42.89 mGy. CTDIVOL of males and of females presents a statistically significant difference (p < 0.05). The 75th percentile of CTDIVOL of males was 45.42 mGy and 75th percentile of CTIVOL of females was 41.33 mGy. Values of CTDIVOL of exposed males were 9% higher than values of CTDIVOL of exposed females. The 75th percentiles of CTDIVOL at individual departments were 35.68, 155.30, 74.01 and 37.58 mGy, respectively (Figure 3). Figure 3. View largeDownload slide Values of CTDIVOL of individual departments in study. Figure 3. View largeDownload slide Values of CTDIVOL of individual departments in study. The DLP of all patients ranged from 45.00 to 2756.00 mGy cm. The 75th percentile of DLP of patients in the study was 509.00 mGy cm. There was a statistically significant difference between the DLP of males and females (p < 0.05). The 75th percentile of DLP of males was 570.75 mGy cm and of females was 474.25 mGy cm. The DLP of males was 17% higher than the DLP of females. At individual departments were 441.00, 779.80, 974.00 and 588.50 mGy cm, respectively (Figure 4). Figure 4. View largeDownload slide Values of DLP of individual departments in study. Figure 4. View largeDownload slide Values of DLP of individual departments in study. Specific values of CTDIVOL and DLP in all patients of study are in Table 3. In Tables 4 and 5 are values of CTDIVOL and DLP of individual departments. In Table 6 are given the values of CTDIVOL and DLP according to the BMI. Table 3. Value of CTDIVOL and DLP of patients in study. Parameters Females Males Both CTDIVOL (mGy) Median ± SD 75th percentile Min–Max 30.36 ± 29.13 31.30 ± 43.30 30.82 ± 36.54 41.33 45.42 42.89 7.47–272.00 9.16–267.50 7.47–272.00 DLP (mGy cm) Median ± SD 75th percentile Min–Max 353.00 ± 256.18 382.50 ± 358.17 367.00 ± 309.60 474.25 570.75 509.00 45.00–2425.00 55.00–2756.00 45.00–2756.00 Effective dose (mSv) Median ± SD 75th percentile Min–Max 6.02 ± 4.36 6.50 ± 6.09 6.25 ± 5.27 0.77–41.23 0.94–46.85 8.66 8.07 9.70 0.77–46.85 Parameters Females Males Both CTDIVOL (mGy) Median ± SD 75th percentile Min–Max 30.36 ± 29.13 31.30 ± 43.30 30.82 ± 36.54 41.33 45.42 42.89 7.47–272.00 9.16–267.50 7.47–272.00 DLP (mGy cm) Median ± SD 75th percentile Min–Max 353.00 ± 256.18 382.50 ± 358.17 367.00 ± 309.60 474.25 570.75 509.00 45.00–2425.00 55.00–2756.00 45.00–2756.00 Effective dose (mSv) Median ± SD 75th percentile Min–Max 6.02 ± 4.36 6.50 ± 6.09 6.25 ± 5.27 0.77–41.23 0.94–46.85 8.66 8.07 9.70 0.77–46.85 Table 3. Value of CTDIVOL and DLP of patients in study. Parameters Females Males Both CTDIVOL (mGy) Median ± SD 75th percentile Min–Max 30.36 ± 29.13 31.30 ± 43.30 30.82 ± 36.54 41.33 45.42 42.89 7.47–272.00 9.16–267.50 7.47–272.00 DLP (mGy cm) Median ± SD 75th percentile Min–Max 353.00 ± 256.18 382.50 ± 358.17 367.00 ± 309.60 474.25 570.75 509.00 45.00–2425.00 55.00–2756.00 45.00–2756.00 Effective dose (mSv) Median ± SD 75th percentile Min–Max 6.02 ± 4.36 6.50 ± 6.09 6.25 ± 5.27 0.77–41.23 0.94–46.85 8.66 8.07 9.70 0.77–46.85 Parameters Females Males Both CTDIVOL (mGy) Median ± SD 75th percentile Min–Max 30.36 ± 29.13 31.30 ± 43.30 30.82 ± 36.54 41.33 45.42 42.89 7.47–272.00 9.16–267.50 7.47–272.00 DLP (mGy cm) Median ± SD 75th percentile Min–Max 353.00 ± 256.18 382.50 ± 358.17 367.00 ± 309.60 474.25 570.75 509.00 45.00–2425.00 55.00–2756.00 45.00–2756.00 Effective dose (mSv) Median ± SD 75th percentile Min–Max 6.02 ± 4.36 6.50 ± 6.09 6.25 ± 5.27 0.77–41.23 0.94–46.85 8.66 8.07 9.70 0.77–46.85 Table 4. Value of CTDIVOL of patients in individual departments in study. Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 29.08 ± 11.05 10.23–91.07 36.30 28.27 ± 10.77 10.21–98.79 35.20 28.70 ± 10.89 10.21–98.79 35.68 B Males Females Both 138.30 ± 61.13 39.20–267.50 179.30 80.30 ± 47.15 36.80–272.00 123.80 97.70 ± 57.98 36.80–272.00 155.30 C Males Females Both 40.31 ± 41.85 9.86–197.37 82.81 30.43 ± 36.05 7.47–149.44 68.13 37.48 ± 39.53 7.47–197.37 74.01 D Males Females Both 30.17 ± 10.76 9.16–67.17 37.13 31.61 ± 11.69 8.60–74.92 38.52 30.81 ± 11.15 8.60–74.92 37.58 Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 29.08 ± 11.05 10.23–91.07 36.30 28.27 ± 10.77 10.21–98.79 35.20 28.70 ± 10.89 10.21–98.79 35.68 B Males Females Both 138.30 ± 61.13 39.20–267.50 179.30 80.30 ± 47.15 36.80–272.00 123.80 97.70 ± 57.98 36.80–272.00 155.30 C Males Females Both 40.31 ± 41.85 9.86–197.37 82.81 30.43 ± 36.05 7.47–149.44 68.13 37.48 ± 39.53 7.47–197.37 74.01 D Males Females Both 30.17 ± 10.76 9.16–67.17 37.13 31.61 ± 11.69 8.60–74.92 38.52 30.81 ± 11.15 8.60–74.92 37.58 Table 4. Value of CTDIVOL of patients in individual departments in study. Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 29.08 ± 11.05 10.23–91.07 36.30 28.27 ± 10.77 10.21–98.79 35.20 28.70 ± 10.89 10.21–98.79 35.68 B Males Females Both 138.30 ± 61.13 39.20–267.50 179.30 80.30 ± 47.15 36.80–272.00 123.80 97.70 ± 57.98 36.80–272.00 155.30 C Males Females Both 40.31 ± 41.85 9.86–197.37 82.81 30.43 ± 36.05 7.47–149.44 68.13 37.48 ± 39.53 7.47–197.37 74.01 D Males Females Both 30.17 ± 10.76 9.16–67.17 37.13 31.61 ± 11.69 8.60–74.92 38.52 30.81 ± 11.15 8.60–74.92 37.58 Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 29.08 ± 11.05 10.23–91.07 36.30 28.27 ± 10.77 10.21–98.79 35.20 28.70 ± 10.89 10.21–98.79 35.68 B Males Females Both 138.30 ± 61.13 39.20–267.50 179.30 80.30 ± 47.15 36.80–272.00 123.80 97.70 ± 57.98 36.80–272.00 155.30 C Males Females Both 40.31 ± 41.85 9.86–197.37 82.81 30.43 ± 36.05 7.47–149.44 68.13 37.48 ± 39.53 7.47–197.37 74.01 D Males Females Both 30.17 ± 10.76 9.16–67.17 37.13 31.61 ± 11.69 8.60–74.92 38.52 30.81 ± 11.15 8.60–74.92 37.58 Table 5. Value of DLP of patients in individual departments in study. Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 351.00 ± 192.09 55.00–1497.00 431.00 333.00 ± 169.84 47.00–1300.00 427.00 337.50 ± 179.85 47.00–1497.00 441.00 B Males Females Both 652.60 ± 310.52 123.50–1539.30 895.20 427.50 ± 295.97 199.80–1621.60 627.50 503.10 ± 312.90 123.50–1621.60 779.80 C Males Females Both 494.50 ± 690.93 56.00–2756.00 1220.75 339.00 ± 526.66 45.00–2425.00 862.00 441.00 ± 627.29 45.00–2756.00 974.00 D Males Females Both 439.00 ± 227.43 111.00–1439.00 597.00 463.50 ± 173.19 125.00–932.00 549.50 450.50 ± 205.18 111.00–1439.00 588.50 Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 351.00 ± 192.09 55.00–1497.00 431.00 333.00 ± 169.84 47.00–1300.00 427.00 337.50 ± 179.85 47.00–1497.00 441.00 B Males Females Both 652.60 ± 310.52 123.50–1539.30 895.20 427.50 ± 295.97 199.80–1621.60 627.50 503.10 ± 312.90 123.50–1621.60 779.80 C Males Females Both 494.50 ± 690.93 56.00–2756.00 1220.75 339.00 ± 526.66 45.00–2425.00 862.00 441.00 ± 627.29 45.00–2756.00 974.00 D Males Females Both 439.00 ± 227.43 111.00–1439.00 597.00 463.50 ± 173.19 125.00–932.00 549.50 450.50 ± 205.18 111.00–1439.00 588.50 Table 5. Value of DLP of patients in individual departments in study. Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 351.00 ± 192.09 55.00–1497.00 431.00 333.00 ± 169.84 47.00–1300.00 427.00 337.50 ± 179.85 47.00–1497.00 441.00 B Males Females Both 652.60 ± 310.52 123.50–1539.30 895.20 427.50 ± 295.97 199.80–1621.60 627.50 503.10 ± 312.90 123.50–1621.60 779.80 C Males Females Both 494.50 ± 690.93 56.00–2756.00 1220.75 339.00 ± 526.66 45.00–2425.00 862.00 441.00 ± 627.29 45.00–2756.00 974.00 D Males Females Both 439.00 ± 227.43 111.00–1439.00 597.00 463.50 ± 173.19 125.00–932.00 549.50 450.50 ± 205.18 111.00–1439.00 588.50 Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 351.00 ± 192.09 55.00–1497.00 431.00 333.00 ± 169.84 47.00–1300.00 427.00 337.50 ± 179.85 47.00–1497.00 441.00 B Males Females Both 652.60 ± 310.52 123.50–1539.30 895.20 427.50 ± 295.97 199.80–1621.60 627.50 503.10 ± 312.90 123.50–1621.60 779.80 C Males Females Both 494.50 ± 690.93 56.00–2756.00 1220.75 339.00 ± 526.66 45.00–2425.00 862.00 441.00 ± 627.29 45.00–2756.00 974.00 D Males Females Both 439.00 ± 227.43 111.00–1439.00 597.00 463.50 ± 173.19 125.00–932.00 549.50 450.50 ± 205.18 111.00–1439.00 588.50 Table 6. Value of CTDIVOL and DLP by BMI of patients in study. BMI DLP (mGy cm) CTDIVOL (mGy) 18.5–24.9 Median 273.00 24.35 75th percentile 356.50 30.76 25–29.9 Median 314.00 27.65 75th percentile 402.90 35.20 30–34.9 Median 399.00 33.46 75th percentile 539.00 45.86 35–39.9 Median 497.50 39.31 75th percentile 648.25 63.02 40< Median 602.50 47.80 75th percentile 772.60 58.25 BMI DLP (mGy cm) CTDIVOL (mGy) 18.5–24.9 Median 273.00 24.35 75th percentile 356.50 30.76 25–29.9 Median 314.00 27.65 75th percentile 402.90 35.20 30–34.9 Median 399.00 33.46 75th percentile 539.00 45.86 35–39.9 Median 497.50 39.31 75th percentile 648.25 63.02 40< Median 602.50 47.80 75th percentile 772.60 58.25 Table 6. Value of CTDIVOL and DLP by BMI of patients in study. BMI DLP (mGy cm) CTDIVOL (mGy) 18.5–24.9 Median 273.00 24.35 75th percentile 356.50 30.76 25–29.9 Median 314.00 27.65 75th percentile 402.90 35.20 30–34.9 Median 399.00 33.46 75th percentile 539.00 45.86 35–39.9 Median 497.50 39.31 75th percentile 648.25 63.02 40< Median 602.50 47.80 75th percentile 772.60 58.25 BMI DLP (mGy cm) CTDIVOL (mGy) 18.5–24.9 Median 273.00 24.35 75th percentile 356.50 30.76 25–29.9 Median 314.00 27.65 75th percentile 402.90 35.20 30–34.9 Median 399.00 33.46 75th percentile 539.00 45.86 35–39.9 Median 497.50 39.31 75th percentile 648.25 63.02 40< Median 602.50 47.80 75th percentile 772.60 58.25 The median effective dose of patients in our study was 6.25 mSv and the 75th percentile of effective dose was 8.66 mSv (Table 3). At individual departments were the median values of effective dose 5.75, 8.55, 7.40 and 7.65 mSv, respectively (Figure 5). Figure 5. View largeDownload slide Values of effective dose of individual departments in study. Figure 5. View largeDownload slide Values of effective dose of individual departments in study. DISCUSSION The reduction of radiation burden and the optimization of examinations in order to minimize the risk of the occurrence of stochastic effects associated with high dose medical exposure is the key concept of radiation protection. Creation of national DRLs is one of the main tools for promoting that the optimization was implemented. Its use can help to the staff of radiological departments to conduct CCTA examinations with lower doses. Data which compare significant differences between exposures in different regions or countries and also exposures from different types of examinations, or trends in innovations of examinations, have been published by Compagnone et al.(10) The last published results of the national DRLs for the CCTA examinations focused the attention of scientists in radiation protection in many countries on the importance of their use in practice. The results of DRLs in our study correspond to results of meta-analysis of experimental results published by Alhailiy, where the range of DRLs delivered by DLP was from 671 to 1510 mGy cm and the range of the DRLs delivered by CTDIVOL was from 26 to 70 mGy. It can be seen that there is a great variability of methodologies by which the DRLs are proposed in each study(11). A French study has also shown that the CCTA examinations are associated with great variability of DLP. The reason for this variability can be explained by the applied modality of CCTA and by the type of the used CT device(12). The variability of radiation dose according to the type of CT device has been described elsewhere(13). The values of 75th percentile of the CTDIVOL and DLP that are proposed as national DRL in the Slovak Republic are comparable with the values of the CTDIVOL and DLP from other studies mainly that published in France(14). On the contrary, the DRLs created by us are ~50% lower than the DRLs, which are proposed in Japan or Iran(15, 16) (Table 7). Table 7. Value of CTDIVOL and DLP in other study. Country CTDIVOL (mGy) DLP (mGy cm) Iran(14) 67 1073 Slovak Republic 45 510 France(15) 26 (PT CCTA), 44 (RG CCTA) 370 (PT CCTA), 870 (RG CCTA) Japan(16) 90 1400 Country CTDIVOL (mGy) DLP (mGy cm) Iran(14) 67 1073 Slovak Republic 45 510 France(15) 26 (PT CCTA), 44 (RG CCTA) 370 (PT CCTA), 870 (RG CCTA) Japan(16) 90 1400 Table 7. Value of CTDIVOL and DLP in other study. Country CTDIVOL (mGy) DLP (mGy cm) Iran(14) 67 1073 Slovak Republic 45 510 France(15) 26 (PT CCTA), 44 (RG CCTA) 370 (PT CCTA), 870 (RG CCTA) Japan(16) 90 1400 Country CTDIVOL (mGy) DLP (mGy cm) Iran(14) 67 1073 Slovak Republic 45 510 France(15) 26 (PT CCTA), 44 (RG CCTA) 370 (PT CCTA), 870 (RG CCTA) Japan(16) 90 1400 The value of national Slovak DRL proposed from our study, expressed by CTDIVOL is 45 mGy and that expressed by DLP is 510 mGy cm. The DRL created for the CCTA, includes the PT CCTA, as well as, the RG CCTA. Choice of the type of the examination between these two modalities depends on the heart rate of patients during exposure. As it is evident from our results, only one department (department A) met the proposed Slovak national DRL value. We can assume that the reason why only one department A met the proposed DRLs is that in the department A was used more PT CCTA procedures than RG CCTA. We assume that department A has more experience with implementing PT CCTA because this department was the first department in Slovakia which the CCTA examination started to do. Their more experienced and trained laboratory technicians are able to adjust values of heart rate as well as exposure parameters of patients so that exposure to CCTA was as low as it is possible. However, the major limitation of our study is, that we do not have enough information about the choice of modality of CCTA (PT CCTA or RG CCTA), because departments do not record this information. It is interesting to notice, that departments B and C showed a statistically significant difference in the size of CTDIVOL and the size of DLP. At department C, the values of CTDIVOL for males were 25% higher and that of DLP 31% higher than values for females. These results are interesting because the parameters of CTDIVOL and DLP of males are higher than parameters of females, but the values of BMI of females (75th percentile BMI is 33 kg/m2) are higher than values of BMI of males (75th percentile BMI is 32 kg/m2). The cause of evidence of higher values of CTDIVOL and DLP of males compared with values of CTDIVOL and DLP of females, in spite of higher BMI of females, may be the occurrence of higher heart rate of males. We assume that heart rate of patient during CCTA examination is more affected by exposure than by BMI alone. However, the association between the value of heart rate and that of effective dose cannot be confirmed or refused because the values of heart rate of patients in the individual departments, was not recorded. From this reason, this assumption must be verified by a new study in which we will examine the impact of other factors (other than the physical parameters of the CCTA examination) that could affect the magnitude of the exposure. At the department B, the values of CTDIVOL of males were 42% higher than females and the values of DLP of males were 34% higher than the values of DLP of females. At the department B was BMI values of males (75th percentile BMI is 35 kg/m2) higher than BMI values of females (75th percentile BMI is 34 kg/m2). Optimization and dose reduction of CCTA examinations could be realized by the change of the physical parameters of the examination, by taking into account the BMI of patients, and by following the heart rate of patients and the R-R interval during exposure. An important step of optimization of exposure is an individual approach to every patient. In this process the proper regulation of radiation protection legislation and the introduction of a national DRL for the CCTA examinations are of great importance. However, it has been shown that our study has some limitations and needs to be re-performed. Getting answers to questions that arose based on our past results will be the subject of a further study that takes into account more factors, such as modality of CCTA examination, value of heart rate during exposure, blood pressure and more. View largeDownload slide Legend for the boxplot for Figures 1 to 5. View largeDownload slide Legend for the boxplot for Figures 1 to 5. CONCLUSION As in many international studies with similar task, our study highlights the need to create the national DRLs for CCTA, because it is an examination with rapid increasing frequency, mainly due to the raise of mortality and morbidity caused by cardiovascular diseases. Due to the sufficient number of observations in our study, the obtained value of the DRL can be proposed as a national DRL for the Slovak Republic. REFERENCES 1 The organisation for economic cooperation and development . Computed tomography (CT) scanners. Available on https://data.oecd.org/healtheqt/computed-tomography-ct-scanners.htm (28 May 2017 , date last accessed). 2 The organisation for economic cooperation and development . Computed tomography (CT) exams. Available on https://data.oecd.org/healthcare/computed-tomography-ct-exams.htm (28 May 2017 , date last accessed). 3 Nieman , K. Can CT angiography replace catheter coronary angiography? EuroIntervention 6 , 65 – 71 ( 2010 ). 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Estimated radiation dose associated with cardiac CT angiography . J Am Med Assoc 301 ( 5 ), 500 – 507 ( 2009 ). Google Scholar CrossRef Search ADS 13 Fink , Ch. et al. . Radiation dose at coronary CT angiography: second-generation dual-source CT versus single-source 64-MDCT and first-generation dual-source CT . Am. J. Roentgenol. 196 ( 5 ), 550 – 557 ( 2011 ). Google Scholar CrossRef Search ADS 14 Mafalanka , F. et al. . Establishment of diagnostic reference levels in cardiac CT in France: a need for patient dose optimisation . Radiat. Prot. Dosim. 164 ( 1–2 ), 116 – 119 ( 2014 ). 15 Nasab , S. M. B. H. et al. . Estimation of cardiac CT angiography radiation dose toward the establishment of national diagnostic reference level for CCTA in Iran . Radiat. Prot. Dosim. 174 ( 4 ), 551 – 557 ( 2017 ). 16 Japan Association on Radiological Protection in Medicine et al . Diagnostic reference levels. Based on latest surveys in Japan.Japan DRLs 2015. Available on http://www.radher.jp/J-RIME/report/DRLhoukokusyoEng.pdf (29 August 2017 , date last accessed). © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiation Protection Dosimetry Oxford University Press

ESTIMATION OF DIAGNOSTIC REFERENCE LEVELS FOR CT CORONAROGRAPHY IN SLOVAKIA

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Abstract

Abstract The coronary CT angiography (CCTA) is a frequent diagnostic method connected with large variability of effective dose. Therefore, it is the type of examination where optimization is very important and the use of a national diagnostic reference level (DRL) recommended. In Slovakia the DRL for interventional radiology examinations until now fails. The objective of our study was to propose the national DRL for CCTA examinations in Slovak Republic, on the basis of a cross-sectional multicenter study, performed in four departments of radiology. The study was realized in 2014–16 in a sample of 1725 patients undergoing CCTA examination. The proposed DRL expressed by CTDIVOL is 45 mGy and of DLP is 510 mGy cm. Over the last 10 years, the number of CT devices that are used in the Slovak Republic has increased by more than 43% and this leads to an increase in the number of CT examinations performed, representing nowadays ~135 examinations per 1000 inhabitants in Slovak Republic per year(1, 2). More frequent use of computer tomography is manifested in most medical disciplines, including cardiology. One of the newest diagnostic imaging methods in cardiology is the coronary CT angiography (CCTA). The rapid technological development and introduction of the CCTA into practice has led to cause questions in the scientific sphere about whether this diagnostic method is suitable as an alternative for invasive coronarography(3). These questions and uncertainties lead to the inception of many scientific studies whose primary objective was to compare invasive and non-invasive coronarography(4–7). The main argument against CCTA was the excessive use of x-rays. Earlier studies have noted that an effective dose of CCTA was higher than 20 mSv, which corresponded with ~7-year exposure from natural radiation(8). Since then, significant progress has been made and new methodologies have been developed which could reduce the effective dose by more than 50%(9). In addition to the process of introducing new methodologies and adjusting the physical parameters of examination, the Slovak national DRLs have been proposed. The DRL for CCTA is formulated by the values of volume CT dose index (CTDIVOL) and the dose–length product (DLP). CCTA is increasingly frequent diagnostic method, so a national value of DRL for CCTA is appropriate in the Slovak Republic. The objective of our study was to prepare a draft of national DRL for the Slovak Republic for the examination of the heart by CCTA. Our study is the first study in Slovakia which proposes DRL values for CT angiography protocols in this country. METHODOLOGY We performed a cross-sectional multicentre study in the Slovak Republic, with participation of four departments of radiology performing CCTA. This number of departments covers 70% of all departments of radiology in the Slovak Republic, which perform CCTA examinations. The participating departments of radiology were marked with characters A, B, C and D. The CCTA were performed according to the individual status of patient with a prospective method of ECG-gating (PT CCTA) or with a retrospective ECG-gating (RG CCTA). This study included 1725 patients, of which were 931 females and 794 males. Each patient had received the Topogram, the Coronary Artery Calcium Score and the CCTA. Exposure parameters for the study were obtained from the hospital archiving system. For statistical analysis we used the statistical software R-Project version 2.11.1 and Microsoft Office Excel 2007. For the objective of creating national DRLs we established the 75th percentile of dose distribution (CTDIVOL and DLP). The effective dose was calculate by converting DLP with k-factors from European Commission 0.017 mSv/(mGy cm). Basic characteristics were used for calculation of mean, median, minimum and maximum values, for 75th percentile and for standard deviation. Correlation and regression were used for data analysis and statistical test: Kolmogorov–Smirnov test, Wilcoxon test, T-test, Anova test and Kruskal–Wallis test. Statistical significance was set at a value lower than 0.05 (p < 0.05). The study was approved by the ethics committee and was carried out in accordance with the law on the protection of personal dates of patients. RESULTS In the study were 1725 patients (54% of females and 46% of males). Patients in the study were from 13 to 89 years old. The mean age of patients in the study was 61 years. The mean age of females was 63 years, with females from 50 to 79 years accounting 88% of all females. The mean age of males was 59 years, with males from 50 to 79 years accounting 76% of all males. The mean BMI of patients in the study was 29 kg/m2, with 75% of patients in the study having BMI of up to 32 kg/m2. Healthy BMI (20–25 kg/m2) was observed in only 22% of all patients and up to 36% of patients had obesity. The description of the personal characteristics of the patients involved in the study is in Table 1. Table 2 shows the specific numbers and characteristics of patients of individual departments of the study. Table 1. Basic characteristics of the file in the study. Gender Number Age BMI (kg/m2) Males 46% (N = 794) 59 ± 12 30 ± 5 Females 54% (N = 931) 63 ± 11 29 ± 6 Both 100% (N = 1725) 61 ± 12 29 ± 5 Gender Number Age BMI (kg/m2) Males 46% (N = 794) 59 ± 12 30 ± 5 Females 54% (N = 931) 63 ± 11 29 ± 6 Both 100% (N = 1725) 61 ± 12 29 ± 5 Table 1. Basic characteristics of the file in the study. Gender Number Age BMI (kg/m2) Males 46% (N = 794) 59 ± 12 30 ± 5 Females 54% (N = 931) 63 ± 11 29 ± 6 Both 100% (N = 1725) 61 ± 12 29 ± 5 Gender Number Age BMI (kg/m2) Males 46% (N = 794) 59 ± 12 30 ± 5 Females 54% (N = 931) 63 ± 11 29 ± 6 Both 100% (N = 1725) 61 ± 12 29 ± 5 Table 2. Basic characteristics of patients of individual departments in the study. Department Number Age BMI (kg/m2) A 66% (N = 1136) 61 ± 11 29 ± 5 B 11% (N = 194) 62 ± 10 34 ± 6 C 12% (N = 203) 65 ± 10 32 ± 5 D 11% (N = 192) 59 ± 12 — Department Number Age BMI (kg/m2) A 66% (N = 1136) 61 ± 11 29 ± 5 B 11% (N = 194) 62 ± 10 34 ± 6 C 12% (N = 203) 65 ± 10 32 ± 5 D 11% (N = 192) 59 ± 12 — Table 2. Basic characteristics of patients of individual departments in the study. Department Number Age BMI (kg/m2) A 66% (N = 1136) 61 ± 11 29 ± 5 B 11% (N = 194) 62 ± 10 34 ± 6 C 12% (N = 203) 65 ± 10 32 ± 5 D 11% (N = 192) 59 ± 12 — Department Number Age BMI (kg/m2) A 66% (N = 1136) 61 ± 11 29 ± 5 B 11% (N = 194) 62 ± 10 34 ± 6 C 12% (N = 203) 65 ± 10 32 ± 5 D 11% (N = 192) 59 ± 12 — Examinations of CCTA were performed mostly at a voltage of 120 kV and using an automatic system for adjusting exposure parameters. The most important parameters for the DRL of CCTA are CTDIVOL and DLP. Figure 1 shows the distribution of CTDIVOL and DLP of exposed patients, Figure 2 presents values of CTDIVOL and DLP of patients by gender. Figure 1. View largeDownload slide Frequency of CTDIVOL and DLP of file in the study. (A) Frequency of DLP of patients. (B) Frequency of CTDIVOL of patients. Figure 1. View largeDownload slide Frequency of CTDIVOL and DLP of file in the study. (A) Frequency of DLP of patients. (B) Frequency of CTDIVOL of patients. Figure 2. View largeDownload slide Values of CTDIVOL and DLP of file in the study. (A) Values of DLP of patients. (B) Values of CTDIVOL of patients. Figure 2. View largeDownload slide Values of CTDIVOL and DLP of file in the study. (A) Values of DLP of patients. (B) Values of CTDIVOL of patients. The CTDIVOL of all patients was ranged from 7.47 to 272.00 mGy. The 75th percentile of CTDIVOL was 42.89 mGy. CTDIVOL of males and of females presents a statistically significant difference (p < 0.05). The 75th percentile of CTDIVOL of males was 45.42 mGy and 75th percentile of CTIVOL of females was 41.33 mGy. Values of CTDIVOL of exposed males were 9% higher than values of CTDIVOL of exposed females. The 75th percentiles of CTDIVOL at individual departments were 35.68, 155.30, 74.01 and 37.58 mGy, respectively (Figure 3). Figure 3. View largeDownload slide Values of CTDIVOL of individual departments in study. Figure 3. View largeDownload slide Values of CTDIVOL of individual departments in study. The DLP of all patients ranged from 45.00 to 2756.00 mGy cm. The 75th percentile of DLP of patients in the study was 509.00 mGy cm. There was a statistically significant difference between the DLP of males and females (p < 0.05). The 75th percentile of DLP of males was 570.75 mGy cm and of females was 474.25 mGy cm. The DLP of males was 17% higher than the DLP of females. At individual departments were 441.00, 779.80, 974.00 and 588.50 mGy cm, respectively (Figure 4). Figure 4. View largeDownload slide Values of DLP of individual departments in study. Figure 4. View largeDownload slide Values of DLP of individual departments in study. Specific values of CTDIVOL and DLP in all patients of study are in Table 3. In Tables 4 and 5 are values of CTDIVOL and DLP of individual departments. In Table 6 are given the values of CTDIVOL and DLP according to the BMI. Table 3. Value of CTDIVOL and DLP of patients in study. Parameters Females Males Both CTDIVOL (mGy) Median ± SD 75th percentile Min–Max 30.36 ± 29.13 31.30 ± 43.30 30.82 ± 36.54 41.33 45.42 42.89 7.47–272.00 9.16–267.50 7.47–272.00 DLP (mGy cm) Median ± SD 75th percentile Min–Max 353.00 ± 256.18 382.50 ± 358.17 367.00 ± 309.60 474.25 570.75 509.00 45.00–2425.00 55.00–2756.00 45.00–2756.00 Effective dose (mSv) Median ± SD 75th percentile Min–Max 6.02 ± 4.36 6.50 ± 6.09 6.25 ± 5.27 0.77–41.23 0.94–46.85 8.66 8.07 9.70 0.77–46.85 Parameters Females Males Both CTDIVOL (mGy) Median ± SD 75th percentile Min–Max 30.36 ± 29.13 31.30 ± 43.30 30.82 ± 36.54 41.33 45.42 42.89 7.47–272.00 9.16–267.50 7.47–272.00 DLP (mGy cm) Median ± SD 75th percentile Min–Max 353.00 ± 256.18 382.50 ± 358.17 367.00 ± 309.60 474.25 570.75 509.00 45.00–2425.00 55.00–2756.00 45.00–2756.00 Effective dose (mSv) Median ± SD 75th percentile Min–Max 6.02 ± 4.36 6.50 ± 6.09 6.25 ± 5.27 0.77–41.23 0.94–46.85 8.66 8.07 9.70 0.77–46.85 Table 3. Value of CTDIVOL and DLP of patients in study. Parameters Females Males Both CTDIVOL (mGy) Median ± SD 75th percentile Min–Max 30.36 ± 29.13 31.30 ± 43.30 30.82 ± 36.54 41.33 45.42 42.89 7.47–272.00 9.16–267.50 7.47–272.00 DLP (mGy cm) Median ± SD 75th percentile Min–Max 353.00 ± 256.18 382.50 ± 358.17 367.00 ± 309.60 474.25 570.75 509.00 45.00–2425.00 55.00–2756.00 45.00–2756.00 Effective dose (mSv) Median ± SD 75th percentile Min–Max 6.02 ± 4.36 6.50 ± 6.09 6.25 ± 5.27 0.77–41.23 0.94–46.85 8.66 8.07 9.70 0.77–46.85 Parameters Females Males Both CTDIVOL (mGy) Median ± SD 75th percentile Min–Max 30.36 ± 29.13 31.30 ± 43.30 30.82 ± 36.54 41.33 45.42 42.89 7.47–272.00 9.16–267.50 7.47–272.00 DLP (mGy cm) Median ± SD 75th percentile Min–Max 353.00 ± 256.18 382.50 ± 358.17 367.00 ± 309.60 474.25 570.75 509.00 45.00–2425.00 55.00–2756.00 45.00–2756.00 Effective dose (mSv) Median ± SD 75th percentile Min–Max 6.02 ± 4.36 6.50 ± 6.09 6.25 ± 5.27 0.77–41.23 0.94–46.85 8.66 8.07 9.70 0.77–46.85 Table 4. Value of CTDIVOL of patients in individual departments in study. Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 29.08 ± 11.05 10.23–91.07 36.30 28.27 ± 10.77 10.21–98.79 35.20 28.70 ± 10.89 10.21–98.79 35.68 B Males Females Both 138.30 ± 61.13 39.20–267.50 179.30 80.30 ± 47.15 36.80–272.00 123.80 97.70 ± 57.98 36.80–272.00 155.30 C Males Females Both 40.31 ± 41.85 9.86–197.37 82.81 30.43 ± 36.05 7.47–149.44 68.13 37.48 ± 39.53 7.47–197.37 74.01 D Males Females Both 30.17 ± 10.76 9.16–67.17 37.13 31.61 ± 11.69 8.60–74.92 38.52 30.81 ± 11.15 8.60–74.92 37.58 Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 29.08 ± 11.05 10.23–91.07 36.30 28.27 ± 10.77 10.21–98.79 35.20 28.70 ± 10.89 10.21–98.79 35.68 B Males Females Both 138.30 ± 61.13 39.20–267.50 179.30 80.30 ± 47.15 36.80–272.00 123.80 97.70 ± 57.98 36.80–272.00 155.30 C Males Females Both 40.31 ± 41.85 9.86–197.37 82.81 30.43 ± 36.05 7.47–149.44 68.13 37.48 ± 39.53 7.47–197.37 74.01 D Males Females Both 30.17 ± 10.76 9.16–67.17 37.13 31.61 ± 11.69 8.60–74.92 38.52 30.81 ± 11.15 8.60–74.92 37.58 Table 4. Value of CTDIVOL of patients in individual departments in study. Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 29.08 ± 11.05 10.23–91.07 36.30 28.27 ± 10.77 10.21–98.79 35.20 28.70 ± 10.89 10.21–98.79 35.68 B Males Females Both 138.30 ± 61.13 39.20–267.50 179.30 80.30 ± 47.15 36.80–272.00 123.80 97.70 ± 57.98 36.80–272.00 155.30 C Males Females Both 40.31 ± 41.85 9.86–197.37 82.81 30.43 ± 36.05 7.47–149.44 68.13 37.48 ± 39.53 7.47–197.37 74.01 D Males Females Both 30.17 ± 10.76 9.16–67.17 37.13 31.61 ± 11.69 8.60–74.92 38.52 30.81 ± 11.15 8.60–74.92 37.58 Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 29.08 ± 11.05 10.23–91.07 36.30 28.27 ± 10.77 10.21–98.79 35.20 28.70 ± 10.89 10.21–98.79 35.68 B Males Females Both 138.30 ± 61.13 39.20–267.50 179.30 80.30 ± 47.15 36.80–272.00 123.80 97.70 ± 57.98 36.80–272.00 155.30 C Males Females Both 40.31 ± 41.85 9.86–197.37 82.81 30.43 ± 36.05 7.47–149.44 68.13 37.48 ± 39.53 7.47–197.37 74.01 D Males Females Both 30.17 ± 10.76 9.16–67.17 37.13 31.61 ± 11.69 8.60–74.92 38.52 30.81 ± 11.15 8.60–74.92 37.58 Table 5. Value of DLP of patients in individual departments in study. Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 351.00 ± 192.09 55.00–1497.00 431.00 333.00 ± 169.84 47.00–1300.00 427.00 337.50 ± 179.85 47.00–1497.00 441.00 B Males Females Both 652.60 ± 310.52 123.50–1539.30 895.20 427.50 ± 295.97 199.80–1621.60 627.50 503.10 ± 312.90 123.50–1621.60 779.80 C Males Females Both 494.50 ± 690.93 56.00–2756.00 1220.75 339.00 ± 526.66 45.00–2425.00 862.00 441.00 ± 627.29 45.00–2756.00 974.00 D Males Females Both 439.00 ± 227.43 111.00–1439.00 597.00 463.50 ± 173.19 125.00–932.00 549.50 450.50 ± 205.18 111.00–1439.00 588.50 Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 351.00 ± 192.09 55.00–1497.00 431.00 333.00 ± 169.84 47.00–1300.00 427.00 337.50 ± 179.85 47.00–1497.00 441.00 B Males Females Both 652.60 ± 310.52 123.50–1539.30 895.20 427.50 ± 295.97 199.80–1621.60 627.50 503.10 ± 312.90 123.50–1621.60 779.80 C Males Females Both 494.50 ± 690.93 56.00–2756.00 1220.75 339.00 ± 526.66 45.00–2425.00 862.00 441.00 ± 627.29 45.00–2756.00 974.00 D Males Females Both 439.00 ± 227.43 111.00–1439.00 597.00 463.50 ± 173.19 125.00–932.00 549.50 450.50 ± 205.18 111.00–1439.00 588.50 Table 5. Value of DLP of patients in individual departments in study. Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 351.00 ± 192.09 55.00–1497.00 431.00 333.00 ± 169.84 47.00–1300.00 427.00 337.50 ± 179.85 47.00–1497.00 441.00 B Males Females Both 652.60 ± 310.52 123.50–1539.30 895.20 427.50 ± 295.97 199.80–1621.60 627.50 503.10 ± 312.90 123.50–1621.60 779.80 C Males Females Both 494.50 ± 690.93 56.00–2756.00 1220.75 339.00 ± 526.66 45.00–2425.00 862.00 441.00 ± 627.29 45.00–2756.00 974.00 D Males Females Both 439.00 ± 227.43 111.00–1439.00 597.00 463.50 ± 173.19 125.00–932.00 549.50 450.50 ± 205.18 111.00–1439.00 588.50 Departments Gender Median ± SD Min–Max 75th percentile A Males Females Both 351.00 ± 192.09 55.00–1497.00 431.00 333.00 ± 169.84 47.00–1300.00 427.00 337.50 ± 179.85 47.00–1497.00 441.00 B Males Females Both 652.60 ± 310.52 123.50–1539.30 895.20 427.50 ± 295.97 199.80–1621.60 627.50 503.10 ± 312.90 123.50–1621.60 779.80 C Males Females Both 494.50 ± 690.93 56.00–2756.00 1220.75 339.00 ± 526.66 45.00–2425.00 862.00 441.00 ± 627.29 45.00–2756.00 974.00 D Males Females Both 439.00 ± 227.43 111.00–1439.00 597.00 463.50 ± 173.19 125.00–932.00 549.50 450.50 ± 205.18 111.00–1439.00 588.50 Table 6. Value of CTDIVOL and DLP by BMI of patients in study. BMI DLP (mGy cm) CTDIVOL (mGy) 18.5–24.9 Median 273.00 24.35 75th percentile 356.50 30.76 25–29.9 Median 314.00 27.65 75th percentile 402.90 35.20 30–34.9 Median 399.00 33.46 75th percentile 539.00 45.86 35–39.9 Median 497.50 39.31 75th percentile 648.25 63.02 40< Median 602.50 47.80 75th percentile 772.60 58.25 BMI DLP (mGy cm) CTDIVOL (mGy) 18.5–24.9 Median 273.00 24.35 75th percentile 356.50 30.76 25–29.9 Median 314.00 27.65 75th percentile 402.90 35.20 30–34.9 Median 399.00 33.46 75th percentile 539.00 45.86 35–39.9 Median 497.50 39.31 75th percentile 648.25 63.02 40< Median 602.50 47.80 75th percentile 772.60 58.25 Table 6. Value of CTDIVOL and DLP by BMI of patients in study. BMI DLP (mGy cm) CTDIVOL (mGy) 18.5–24.9 Median 273.00 24.35 75th percentile 356.50 30.76 25–29.9 Median 314.00 27.65 75th percentile 402.90 35.20 30–34.9 Median 399.00 33.46 75th percentile 539.00 45.86 35–39.9 Median 497.50 39.31 75th percentile 648.25 63.02 40< Median 602.50 47.80 75th percentile 772.60 58.25 BMI DLP (mGy cm) CTDIVOL (mGy) 18.5–24.9 Median 273.00 24.35 75th percentile 356.50 30.76 25–29.9 Median 314.00 27.65 75th percentile 402.90 35.20 30–34.9 Median 399.00 33.46 75th percentile 539.00 45.86 35–39.9 Median 497.50 39.31 75th percentile 648.25 63.02 40< Median 602.50 47.80 75th percentile 772.60 58.25 The median effective dose of patients in our study was 6.25 mSv and the 75th percentile of effective dose was 8.66 mSv (Table 3). At individual departments were the median values of effective dose 5.75, 8.55, 7.40 and 7.65 mSv, respectively (Figure 5). Figure 5. View largeDownload slide Values of effective dose of individual departments in study. Figure 5. View largeDownload slide Values of effective dose of individual departments in study. DISCUSSION The reduction of radiation burden and the optimization of examinations in order to minimize the risk of the occurrence of stochastic effects associated with high dose medical exposure is the key concept of radiation protection. Creation of national DRLs is one of the main tools for promoting that the optimization was implemented. Its use can help to the staff of radiological departments to conduct CCTA examinations with lower doses. Data which compare significant differences between exposures in different regions or countries and also exposures from different types of examinations, or trends in innovations of examinations, have been published by Compagnone et al.(10) The last published results of the national DRLs for the CCTA examinations focused the attention of scientists in radiation protection in many countries on the importance of their use in practice. The results of DRLs in our study correspond to results of meta-analysis of experimental results published by Alhailiy, where the range of DRLs delivered by DLP was from 671 to 1510 mGy cm and the range of the DRLs delivered by CTDIVOL was from 26 to 70 mGy. It can be seen that there is a great variability of methodologies by which the DRLs are proposed in each study(11). A French study has also shown that the CCTA examinations are associated with great variability of DLP. The reason for this variability can be explained by the applied modality of CCTA and by the type of the used CT device(12). The variability of radiation dose according to the type of CT device has been described elsewhere(13). The values of 75th percentile of the CTDIVOL and DLP that are proposed as national DRL in the Slovak Republic are comparable with the values of the CTDIVOL and DLP from other studies mainly that published in France(14). On the contrary, the DRLs created by us are ~50% lower than the DRLs, which are proposed in Japan or Iran(15, 16) (Table 7). Table 7. Value of CTDIVOL and DLP in other study. Country CTDIVOL (mGy) DLP (mGy cm) Iran(14) 67 1073 Slovak Republic 45 510 France(15) 26 (PT CCTA), 44 (RG CCTA) 370 (PT CCTA), 870 (RG CCTA) Japan(16) 90 1400 Country CTDIVOL (mGy) DLP (mGy cm) Iran(14) 67 1073 Slovak Republic 45 510 France(15) 26 (PT CCTA), 44 (RG CCTA) 370 (PT CCTA), 870 (RG CCTA) Japan(16) 90 1400 Table 7. Value of CTDIVOL and DLP in other study. Country CTDIVOL (mGy) DLP (mGy cm) Iran(14) 67 1073 Slovak Republic 45 510 France(15) 26 (PT CCTA), 44 (RG CCTA) 370 (PT CCTA), 870 (RG CCTA) Japan(16) 90 1400 Country CTDIVOL (mGy) DLP (mGy cm) Iran(14) 67 1073 Slovak Republic 45 510 France(15) 26 (PT CCTA), 44 (RG CCTA) 370 (PT CCTA), 870 (RG CCTA) Japan(16) 90 1400 The value of national Slovak DRL proposed from our study, expressed by CTDIVOL is 45 mGy and that expressed by DLP is 510 mGy cm. The DRL created for the CCTA, includes the PT CCTA, as well as, the RG CCTA. Choice of the type of the examination between these two modalities depends on the heart rate of patients during exposure. As it is evident from our results, only one department (department A) met the proposed Slovak national DRL value. We can assume that the reason why only one department A met the proposed DRLs is that in the department A was used more PT CCTA procedures than RG CCTA. We assume that department A has more experience with implementing PT CCTA because this department was the first department in Slovakia which the CCTA examination started to do. Their more experienced and trained laboratory technicians are able to adjust values of heart rate as well as exposure parameters of patients so that exposure to CCTA was as low as it is possible. However, the major limitation of our study is, that we do not have enough information about the choice of modality of CCTA (PT CCTA or RG CCTA), because departments do not record this information. It is interesting to notice, that departments B and C showed a statistically significant difference in the size of CTDIVOL and the size of DLP. At department C, the values of CTDIVOL for males were 25% higher and that of DLP 31% higher than values for females. These results are interesting because the parameters of CTDIVOL and DLP of males are higher than parameters of females, but the values of BMI of females (75th percentile BMI is 33 kg/m2) are higher than values of BMI of males (75th percentile BMI is 32 kg/m2). The cause of evidence of higher values of CTDIVOL and DLP of males compared with values of CTDIVOL and DLP of females, in spite of higher BMI of females, may be the occurrence of higher heart rate of males. We assume that heart rate of patient during CCTA examination is more affected by exposure than by BMI alone. However, the association between the value of heart rate and that of effective dose cannot be confirmed or refused because the values of heart rate of patients in the individual departments, was not recorded. From this reason, this assumption must be verified by a new study in which we will examine the impact of other factors (other than the physical parameters of the CCTA examination) that could affect the magnitude of the exposure. At the department B, the values of CTDIVOL of males were 42% higher than females and the values of DLP of males were 34% higher than the values of DLP of females. At the department B was BMI values of males (75th percentile BMI is 35 kg/m2) higher than BMI values of females (75th percentile BMI is 34 kg/m2). Optimization and dose reduction of CCTA examinations could be realized by the change of the physical parameters of the examination, by taking into account the BMI of patients, and by following the heart rate of patients and the R-R interval during exposure. An important step of optimization of exposure is an individual approach to every patient. In this process the proper regulation of radiation protection legislation and the introduction of a national DRL for the CCTA examinations are of great importance. However, it has been shown that our study has some limitations and needs to be re-performed. Getting answers to questions that arose based on our past results will be the subject of a further study that takes into account more factors, such as modality of CCTA examination, value of heart rate during exposure, blood pressure and more. View largeDownload slide Legend for the boxplot for Figures 1 to 5. View largeDownload slide Legend for the boxplot for Figures 1 to 5. CONCLUSION As in many international studies with similar task, our study highlights the need to create the national DRLs for CCTA, because it is an examination with rapid increasing frequency, mainly due to the raise of mortality and morbidity caused by cardiovascular diseases. Due to the sufficient number of observations in our study, the obtained value of the DRL can be proposed as a national DRL for the Slovak Republic. REFERENCES 1 The organisation for economic cooperation and development . Computed tomography (CT) scanners. Available on https://data.oecd.org/healtheqt/computed-tomography-ct-scanners.htm (28 May 2017 , date last accessed). 2 The organisation for economic cooperation and development . Computed tomography (CT) exams. Available on https://data.oecd.org/healthcare/computed-tomography-ct-exams.htm (28 May 2017 , date last accessed). 3 Nieman , K. Can CT angiography replace catheter coronary angiography? EuroIntervention 6 , 65 – 71 ( 2010 ). 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Available on http://www.radher.jp/J-RIME/report/DRLhoukokusyoEng.pdf (29 August 2017 , date last accessed). © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com

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Radiation Protection Dosimetry – Oxford University Press

Published: Feb 16, 2018

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