Original Article
Radiation dose and mortality risk to children undergoing therapeutic interventional cardiology
Acta Radiologica 2015, Vol. 56(7) 867–872 ! The Foundation Acta Radiologica 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0284185114542459 acr.sagepub.com
Shanjun Song1, Chenzhi Liu1 and Menglong Zhang2
Abstract Background: Children undergoing interventional cardiology procedures deserve special concern due to the greater radiation sensitivity of their tissues and more remaining years of life during which a radiation-induced cancer may develop. Purpose: To determine the patient radiation dose for pediatric therapeutic interventional cardiology and to estimate the patient effective dose and lifetime mortality risk to children associated with five common procedures. Material and Methods: Ninety children with congenital heart defects undergoing interventional therapy were enrolled in this study. Data regarding fluoroscopy and radiography time, dose-area product (DAP) and peak skin dose (PSD) for each case were measured. Patients were divided into five groups. The patient effective dose (E) was calculated using a multiplicative model of ICRP 60. The overall lifetime mortality risk was evaluated using appropriate risk coefficients. Results: The mean, median, standard deviation, and range of time, PSD, DAP, and E were presented for the five study groups. When these metrics were considered, there were wide variations for different cases within the same group and statistically significant differences between the five groups. The PSD correlated significantly with DAP (Pearson r ¼ 0.70; P < 0.01), but the correlation in individual cases was poor. For all cases, the range of E was found to be between 0.44 and 66.7 mSv. The corresponding risk of lifetime mortality was 1.16 per thousand. Conclusion: The current study provides overall data on the time, PSD, E, and lifetime mortality risk for pediatric therapeutic interventional cardiology. Radio frequency ablation showed the highest radiation risk.
Keywords Cardiac catheterization, children, interventional therapy, radiation dose Date received: 24 December 2013; accepted: 12 June 2014
Introduction Congenital heart defects are serious diseases that have significant impact on mortality and healthcare costs in children. Approximately 0.8% of infants born each year have a form of a congenital heart disorder (1). Some cases require diagnostic or interventional cardiac catheterization. The radiation exposure to patients and staff in such procedures is much higher than in simple radiographic examinations such as X-rays of the chest or abdomen (2). Interventional radiology procedures have been identified as the third largest contributor to the collective dose after computed tomography (CT) and nuclear medicine (3). Young patients aged 0–19 years undergoing interventional cardiology procedures are potentially at a
three times greater risk of radiation-induced stochastic injuries than adults after aged older than 20 years (4,5). The Alliance for Radiation Safety in Pediatric Imaging has chosen interventional procedures as the second focus of interest after CT (6). Four special metrics have been developed for radiation dose estimation in Fuoroscopic procedures: peak 1 Interventional Department, Liaocheng People’s Hospital, Liaocheng, Shandong, PR China 2 Shandong Medical Imaging Research Institute, Jinan, PR China
Corresponding author: Menglong Zhang, Shandong Medical Imaging Research Institute, Jingwu Road No. 324, Jinan, 250021, PR China. Email: [email protected]
Downloaded from acr.sagepub.com at Yale University Library on July 4, 2015
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Acta Radiologica 56(7)
skin dose (PSD), dose-area product (DAP), cumulative dose (CD), and fluoroscopy and radiography time (abbreviated as time) (7). Furthermore, to evaluate the potential risk of stochastic effects such as cancer and leukemia resulting from cardiac catheterization procedures, effective dose (E) and lifetime mortality risk should be calculated (4). This study has been conducted to measure children’s dose and thus estimate their lifetime mortality risk from therapeutic cardiac interventions. Five common interventional procedures were included in this study: radio frequency (RF) ablation, patent ductus arteriosus (PDA) closure, ventricular septal defect (VSD) closure, atrial septal defect (ASD) closure, and percutaneous balloon pulmonary valvuloplasty (PBPV).
more than 25 years of experience and good knowledge of radiation protection measurements.
Radiation dose Each case included the following registrations: time includes the whole procedure X-ray exposure time (radiography plus fluoroscopy); DAP was taken from the patient records retrospectively; proper calibration of DAP meters was assured by a medical physicist at the beginning of the study; and PSD was measured with a TLD rod (TLD-100 (LiF: Mg: Ti), 1 mm diameter by 6 mm long, made at the Institute of Radiation Medicine, Chinese Academy of Medical Sciences). All interventional procedures in this study included six standard projections. The projections on the body surface and the location of the TLDs were described by Dogan et al. (8) The PSD for each procedure was presumed on one of these projections (9). Five TLD rods were used to form a 2 2 array (one rod in center) TLD that covered a 5 cm 5 cm skin area. These TLD arrays were attached to the patient’s skin for all projections, and the center TLD in each array was placed at the position where the exposure was expected to be at the highest level in each projection. The TLD arrays were more closely arranged and covered a smaller area for children than for adults because of their small sizes. Time was displayed in seconds and was recorded in units of 0.1 min, DAP was displayed in mGycm2 and recorded in Gycm2, and PSD was measured in mGy and recorded in Gy. Patient input exposures were measured both for Fuoroscopy (continuous and pulsed modes) and radiography.
Material and Methods Angiographic equipment All procedures were performed using Allura Xper FD10 angiography system (Philips, Best, The Netherlands). The acquisition parameters such as peak voltage (kVp) and current (mA) were controlled by an automatic exposure control (AEC) system, depending on the size of the patients and the angulations selected. The pulse rates were 30 or 15 pulses/s depending on the complexity of the procedure and the technique of the cardiologist.
Patients and subject selection The patient population included 90 consecutive pediatric patients with congenital heart disease referred for therapeutic cardiac catheterization, aged 0.5–18 years (mean age, 5.7 years). The patients were divided into five groups based on clinical characteristics (Table 1). Clinical data including body weight (BW), height, and age were collected before each procedure. All cardiac catheterizations were performed by two board-certified senior interventional cardiologists with
Effective dose and mortality risk estimation E was obtained from the DAP and BW using the DAP-to-E conversion factor (CF) (10,11). In this study, we adopted consistent tube voltage (65 5 kVp) and filtration (3 mm aluminum). Using the data from Schmidt et al. (10), we calculated the mean CFs at
Table 1. Clinical and demographic characteristics of the patients. Age (years)
Weight (kg)
Height (cm)
Procedure
Cases
Mean
Range
Median
Mean
Range
Median
Mean
Range
Median
PDA closure VSD closure ASD closure RF ablation PBPV
20 22 17 15 16
2.7 4.7 6.7 9.6 5.7
0.5–7.0 2.6–12 2.0–18 4.0–15 1.5–11
2.1 4.0 4.9 11 4.8
13.2 17.3 23.1 28.5 20.2
7.5–22 13.2–32 12–58 16–46 11–35
12.2 16.1 17.8 30 18
93.2 104.0 115.4 132.4 109.0
66–117 88–154 85–160 97–157 80–130
85 101 107 137 103
ASD, atrial septal defect; PBPV, percutaneous balloon pulmonary valvuloplasty; PDA, patent ductus arteriosus; RF, radio frequency; VSD, ventricular septal defect.
Downloaded from acr.sagepub.com at Yale University Library on July 4, 2015
Downloaded from acr.sagepub.com at Yale University Library on July 4, 2015
ANOVA, analysis of variance; ASD, atrial septal defect; DAP, dose-area product; E, effective dose; PBPV, percutaneous balloon pulmonary valvuloplasty; PDA, patent ductus arteriosus; PSD, peak skin dose; RF, radio frequency; s, standard deviation; VSD, ventricular septal defect; x , mean.
1.19–66.71 2.72–25.19 0.66–18.52 0.44–29.83 2.15–7.07 10.3 15.2 11.9 6.6 5.1 4.7 7.7 8.2 3.6 1.9 3.79 0.0069 6.47 29.26 4.85 11.66 6.20 1.29–90.01 5.10–40.82 1.70–21.21 1.79–83.65 3.80–10.68 13.71 20.21 21.29 10.99 10.71 8.35 23.16 26.16 7.11 3.01 4.32 0.0031 0.042 0.12 0.049 0.14 0.074 0.02–0.25 0.04–0.32 0.03–0.41 0.04–1.02 0.04–0.16 2.1–33.0 5.7–43.1 4.1–54.1 5.1–48.1 5.1–21.0
5.67 16.0 6.55 19.3 9.8 11.1 10.3 18.9 10.9 11.5 13.0 19.5 10.7 11.0 5.6 5.24 0.0008
Range
Median
PDA closure VSD closure ASD closure RF ablation PBPV ANOVA F P
0.079 0.080 0.14 0.082 0.091 0.10 0.19 0.24 0.083 0.041 4.41 0.0027
x s Range
Median
DAP (Gy cm2)
x s
The mean, standard deviation, and range of the distribution of time and PSD in interventional procedures were calculated for the five study groups (Table 2). When time and PSD of the patients were studied based on the groups, the results from the different groups differed significantly (P < 0.01). For all cases, the time was in the range of 2.1–54.1 min, and PSD
x s
Results
Procedure
Some data analysis was performed using Excel 2003 (Microsoft). The mean, standard deviation (SD), range of time, PSD, DAP, and E were recorded and calculated for all procedures. Lifetime mortality risk was estimated in general. Analysis of variance (ANOVA) was used to test the significance of the differences among the five groups. The significance level was set at 0.05. Linear regression analysis was used to assess the correlation between the PSD and DAP. The resulted effective dose was compared to several other data acquisitions to determine whether the various dose analogues were sufficiently consistent to suggest that they would be useful for dose monitoring at facilities with otherwise limited resources. All statistical analyses were conducted using the PASW Statistics v18.0 software program (IBM, Armonk, NY, USA).
PSD (Gy)
Data analysis
Time (min)
Here, E is the effective dose derived from Eq. (1), and f is the lifetime mortality risk factor attributable to cardiac interventional radiology. The values of f depend on the child’s age and gender based on the ICRP (4). f varies with age (0–9 years ¼ 16%/Sv [girls] and 13%/Sv [boys]; 10–19 years ¼ 9.5%/Sv [girls] and 7.5%/Sv [boys]). The lifetime mortality risk for overall cases was estimated.
Range
ð2Þ
Table 2. Statistical data for time, PSD, DAP, and E for five groups undergoing therapeutic cardiac intervention.
Risk ¼ f E
Median
The multiplicative model of Publication 60 of the International Commission on Radiological Protection (ICRP) (4) was used to calculate the lifetime probability of death following irradiation, i.e. lifetime mortality risk. The mean lifetime mortality risk due to exposure of children to cardiac intervention can be found using the following formula:
x s
ð1Þ E (mSv)
E ¼ 9:26 kgm Sv Gy1 cm2 DAP=BW
Range
7.45 kg mSv Gy1 and 11.07 kg mSv Gy1 for the posterioranterior and lateral projections, respectively. Given that the viewing direction changes during most procedures and the DAP is logged by our biplane angiographic system only as a sum from both planes, we used an average conversion factor to estimate E:
3.59 10.41 2.72 3.90 2.64
869 Median
Song et al.
870
Acta Radiologica 56(7) Table 3. Comparison between effective dose for therapeutic pediatric cardiac intervention reported in this work and by others. E in this study
E by Yakoumaks (12)
E by El Sayed (13)
Procedure
Mean
3rd quartile
Mean
3rd quartile
Mean
PDA closure VSD closure ASD closure PBPV total
10.3 11.9 5.1 3.6 8.7
11.3 16.5 4.1 3.9 11.3
4.9 6.0 6.3 3.0 5.0
6.8 4.6 7.7 3.2 5.9
6.5 3.3 2.9 6.0
ASD, atrial septal defect; E, effective dose; PBPV, percutaneous balloon pulmonary valvuloplasty; PDA, patent ductus arteriosus; VSD, ventricular septal defect.
was in the range of 0.02–1.02 Gy. The highest PSD was 1.02 Gy for the same patient. One patient who underwent RF ablation had a PSD greater than 1 Gy. Table 2 also summarizes the DAP measurements and E calculations. The mean doses together with the minimum and maximum dose values were tabulated. For all cases, the DAP range was found to be 1.29–90.0 Gy cm2. The corresponding E was (8.7 9.7 mSv), which is higher than the data obtained by Yakoumakis et al. (12) (5.0 4.7 mSv) and by El Sayed et al. (13) (5.97 7.05 mSv) for patients undergoing therapeutic procedures. The E varied widely among the procedures and individual cases in the range of 0.44–66.7 mSv. The highest E for an interventional procedure was calculated for a 2.3-year-old boy weighing 12.5 kg who underwent a PDA closure. The lowest E for an interventional procedure was calculated for a 15-year-old girl weighing 38 kg who underwent RF ablation. One patient that underwent a PDA had a PSD greater than 1 Gy. The third quartile (75th percentile) is often used to establish a reference level (RL) (14,15). We used the third quartile of the distribution of E for all procedures and then compared some of them with data from the literature (12,13). It is apparent from Table 3 that our values for E exceeded those in Yakoumakis’s study in the PDA and VSD closure procedures. The risk value was obtained using E and the risk factor based on the patient’s age. Generally, the risk was 1.16 per thousand. The relationship between two dosimetry characteristics of PSD and DAP was evaluated for all 90 cases. Good correlation was found between PSD and DAP (Pearson r ¼ 0.70; P < 0.01, two-tailed t-test) (Fig. 1). Linear regression yielded a formula for estimation of PSD from DAP: PSD (cGy) ¼ 3.33 þ 0.53 DAP (Gy cm2). However, correlation in individual cases was poor.
Discussion Patient radiation exposure during cardiac catheterizations is relatively high compared to other procedures
Fig. 1. Scatter-plot of DAP and PSD for 90 cases of therapeutic cardiac intervention procedures. The regression line is shown.
involving ionizing radiation. A child receiving a high dose of ionizing radiation has many years for the potential development of malignancies associated with X-ray radiation. Patient radiation dose data should be monitored and recorded for all procedures that are known to be associated with relatively high patient radiation doses (16,17). This study was designed and intended to provide data on ‘‘real-world’’ doses for five cardiac interventional therapy procedures, with no attempt to standardize either the technical factors for each fluoroscopic unit or the way in which each procedure was performed. The dose data in this study represent current practice in our hospital. Generally, there was a wide variation in the doses between the different procedures. Significant differences were observed in time and DAP among the five groups. This was expected because there was no standard technique with which to perform a cardiac catheterization. The radiographic factors and acquisition data depend strongly on the patient’s characteristics and corresponding complexity of the congenital disease.
Downloaded from acr.sagepub.com at Yale University Library on July 4, 2015
Song et al.
871
Table 4. Comparison between DAP/BW for therapeutic pediatric cardiac intervention reported in this work and by others. DAP/BW (Gy cm2 kg–1) in this study
DAP/BW (Gy cm2 kg–1) by Onnasch et al. (28)
Procedure
n
Mean
3rd quartile
n
Mean
3rd quartile
PDA closure VSD closure ASD closure Total
20 22 17 90
0.618 0.803 0.331 0.867
0.363 1.073 0.367 1.091
165 32 259 883
0.347 1.303 0.419 0.559
0.368 1.755 0.500 0.656
ASD, atrial septal defect; BW, body weight; DAP, dose-area product; PDA, patent ductus arteriosus; VSD, ventricular septal defects.
All of the cases we evaluated were radiated with a PSD
Radiation dose and mortality risk to children undergoing therapeutic interventional cardiology
Acta Radiologica 2015, Vol. 56(7) 867–872 ! The Foundation Acta Radiologica 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0284185114542459 acr.sagepub.com
Shanjun Song1, Chenzhi Liu1 and Menglong Zhang2
Abstract Background: Children undergoing interventional cardiology procedures deserve special concern due to the greater radiation sensitivity of their tissues and more remaining years of life during which a radiation-induced cancer may develop. Purpose: To determine the patient radiation dose for pediatric therapeutic interventional cardiology and to estimate the patient effective dose and lifetime mortality risk to children associated with five common procedures. Material and Methods: Ninety children with congenital heart defects undergoing interventional therapy were enrolled in this study. Data regarding fluoroscopy and radiography time, dose-area product (DAP) and peak skin dose (PSD) for each case were measured. Patients were divided into five groups. The patient effective dose (E) was calculated using a multiplicative model of ICRP 60. The overall lifetime mortality risk was evaluated using appropriate risk coefficients. Results: The mean, median, standard deviation, and range of time, PSD, DAP, and E were presented for the five study groups. When these metrics were considered, there were wide variations for different cases within the same group and statistically significant differences between the five groups. The PSD correlated significantly with DAP (Pearson r ¼ 0.70; P < 0.01), but the correlation in individual cases was poor. For all cases, the range of E was found to be between 0.44 and 66.7 mSv. The corresponding risk of lifetime mortality was 1.16 per thousand. Conclusion: The current study provides overall data on the time, PSD, E, and lifetime mortality risk for pediatric therapeutic interventional cardiology. Radio frequency ablation showed the highest radiation risk.
Keywords Cardiac catheterization, children, interventional therapy, radiation dose Date received: 24 December 2013; accepted: 12 June 2014
Introduction Congenital heart defects are serious diseases that have significant impact on mortality and healthcare costs in children. Approximately 0.8% of infants born each year have a form of a congenital heart disorder (1). Some cases require diagnostic or interventional cardiac catheterization. The radiation exposure to patients and staff in such procedures is much higher than in simple radiographic examinations such as X-rays of the chest or abdomen (2). Interventional radiology procedures have been identified as the third largest contributor to the collective dose after computed tomography (CT) and nuclear medicine (3). Young patients aged 0–19 years undergoing interventional cardiology procedures are potentially at a
three times greater risk of radiation-induced stochastic injuries than adults after aged older than 20 years (4,5). The Alliance for Radiation Safety in Pediatric Imaging has chosen interventional procedures as the second focus of interest after CT (6). Four special metrics have been developed for radiation dose estimation in Fuoroscopic procedures: peak 1 Interventional Department, Liaocheng People’s Hospital, Liaocheng, Shandong, PR China 2 Shandong Medical Imaging Research Institute, Jinan, PR China
Corresponding author: Menglong Zhang, Shandong Medical Imaging Research Institute, Jingwu Road No. 324, Jinan, 250021, PR China. Email: [email protected]
Downloaded from acr.sagepub.com at Yale University Library on July 4, 2015
868
Acta Radiologica 56(7)
skin dose (PSD), dose-area product (DAP), cumulative dose (CD), and fluoroscopy and radiography time (abbreviated as time) (7). Furthermore, to evaluate the potential risk of stochastic effects such as cancer and leukemia resulting from cardiac catheterization procedures, effective dose (E) and lifetime mortality risk should be calculated (4). This study has been conducted to measure children’s dose and thus estimate their lifetime mortality risk from therapeutic cardiac interventions. Five common interventional procedures were included in this study: radio frequency (RF) ablation, patent ductus arteriosus (PDA) closure, ventricular septal defect (VSD) closure, atrial septal defect (ASD) closure, and percutaneous balloon pulmonary valvuloplasty (PBPV).
more than 25 years of experience and good knowledge of radiation protection measurements.
Radiation dose Each case included the following registrations: time includes the whole procedure X-ray exposure time (radiography plus fluoroscopy); DAP was taken from the patient records retrospectively; proper calibration of DAP meters was assured by a medical physicist at the beginning of the study; and PSD was measured with a TLD rod (TLD-100 (LiF: Mg: Ti), 1 mm diameter by 6 mm long, made at the Institute of Radiation Medicine, Chinese Academy of Medical Sciences). All interventional procedures in this study included six standard projections. The projections on the body surface and the location of the TLDs were described by Dogan et al. (8) The PSD for each procedure was presumed on one of these projections (9). Five TLD rods were used to form a 2 2 array (one rod in center) TLD that covered a 5 cm 5 cm skin area. These TLD arrays were attached to the patient’s skin for all projections, and the center TLD in each array was placed at the position where the exposure was expected to be at the highest level in each projection. The TLD arrays were more closely arranged and covered a smaller area for children than for adults because of their small sizes. Time was displayed in seconds and was recorded in units of 0.1 min, DAP was displayed in mGycm2 and recorded in Gycm2, and PSD was measured in mGy and recorded in Gy. Patient input exposures were measured both for Fuoroscopy (continuous and pulsed modes) and radiography.
Material and Methods Angiographic equipment All procedures were performed using Allura Xper FD10 angiography system (Philips, Best, The Netherlands). The acquisition parameters such as peak voltage (kVp) and current (mA) were controlled by an automatic exposure control (AEC) system, depending on the size of the patients and the angulations selected. The pulse rates were 30 or 15 pulses/s depending on the complexity of the procedure and the technique of the cardiologist.
Patients and subject selection The patient population included 90 consecutive pediatric patients with congenital heart disease referred for therapeutic cardiac catheterization, aged 0.5–18 years (mean age, 5.7 years). The patients were divided into five groups based on clinical characteristics (Table 1). Clinical data including body weight (BW), height, and age were collected before each procedure. All cardiac catheterizations were performed by two board-certified senior interventional cardiologists with
Effective dose and mortality risk estimation E was obtained from the DAP and BW using the DAP-to-E conversion factor (CF) (10,11). In this study, we adopted consistent tube voltage (65 5 kVp) and filtration (3 mm aluminum). Using the data from Schmidt et al. (10), we calculated the mean CFs at
Table 1. Clinical and demographic characteristics of the patients. Age (years)
Weight (kg)
Height (cm)
Procedure
Cases
Mean
Range
Median
Mean
Range
Median
Mean
Range
Median
PDA closure VSD closure ASD closure RF ablation PBPV
20 22 17 15 16
2.7 4.7 6.7 9.6 5.7
0.5–7.0 2.6–12 2.0–18 4.0–15 1.5–11
2.1 4.0 4.9 11 4.8
13.2 17.3 23.1 28.5 20.2
7.5–22 13.2–32 12–58 16–46 11–35
12.2 16.1 17.8 30 18
93.2 104.0 115.4 132.4 109.0
66–117 88–154 85–160 97–157 80–130
85 101 107 137 103
ASD, atrial septal defect; PBPV, percutaneous balloon pulmonary valvuloplasty; PDA, patent ductus arteriosus; RF, radio frequency; VSD, ventricular septal defect.
Downloaded from acr.sagepub.com at Yale University Library on July 4, 2015
Downloaded from acr.sagepub.com at Yale University Library on July 4, 2015
ANOVA, analysis of variance; ASD, atrial septal defect; DAP, dose-area product; E, effective dose; PBPV, percutaneous balloon pulmonary valvuloplasty; PDA, patent ductus arteriosus; PSD, peak skin dose; RF, radio frequency; s, standard deviation; VSD, ventricular septal defect; x , mean.
1.19–66.71 2.72–25.19 0.66–18.52 0.44–29.83 2.15–7.07 10.3 15.2 11.9 6.6 5.1 4.7 7.7 8.2 3.6 1.9 3.79 0.0069 6.47 29.26 4.85 11.66 6.20 1.29–90.01 5.10–40.82 1.70–21.21 1.79–83.65 3.80–10.68 13.71 20.21 21.29 10.99 10.71 8.35 23.16 26.16 7.11 3.01 4.32 0.0031 0.042 0.12 0.049 0.14 0.074 0.02–0.25 0.04–0.32 0.03–0.41 0.04–1.02 0.04–0.16 2.1–33.0 5.7–43.1 4.1–54.1 5.1–48.1 5.1–21.0
5.67 16.0 6.55 19.3 9.8 11.1 10.3 18.9 10.9 11.5 13.0 19.5 10.7 11.0 5.6 5.24 0.0008
Range
Median
PDA closure VSD closure ASD closure RF ablation PBPV ANOVA F P
0.079 0.080 0.14 0.082 0.091 0.10 0.19 0.24 0.083 0.041 4.41 0.0027
x s Range
Median
DAP (Gy cm2)
x s
The mean, standard deviation, and range of the distribution of time and PSD in interventional procedures were calculated for the five study groups (Table 2). When time and PSD of the patients were studied based on the groups, the results from the different groups differed significantly (P < 0.01). For all cases, the time was in the range of 2.1–54.1 min, and PSD
x s
Results
Procedure
Some data analysis was performed using Excel 2003 (Microsoft). The mean, standard deviation (SD), range of time, PSD, DAP, and E were recorded and calculated for all procedures. Lifetime mortality risk was estimated in general. Analysis of variance (ANOVA) was used to test the significance of the differences among the five groups. The significance level was set at 0.05. Linear regression analysis was used to assess the correlation between the PSD and DAP. The resulted effective dose was compared to several other data acquisitions to determine whether the various dose analogues were sufficiently consistent to suggest that they would be useful for dose monitoring at facilities with otherwise limited resources. All statistical analyses were conducted using the PASW Statistics v18.0 software program (IBM, Armonk, NY, USA).
PSD (Gy)
Data analysis
Time (min)
Here, E is the effective dose derived from Eq. (1), and f is the lifetime mortality risk factor attributable to cardiac interventional radiology. The values of f depend on the child’s age and gender based on the ICRP (4). f varies with age (0–9 years ¼ 16%/Sv [girls] and 13%/Sv [boys]; 10–19 years ¼ 9.5%/Sv [girls] and 7.5%/Sv [boys]). The lifetime mortality risk for overall cases was estimated.
Range
ð2Þ
Table 2. Statistical data for time, PSD, DAP, and E for five groups undergoing therapeutic cardiac intervention.
Risk ¼ f E
Median
The multiplicative model of Publication 60 of the International Commission on Radiological Protection (ICRP) (4) was used to calculate the lifetime probability of death following irradiation, i.e. lifetime mortality risk. The mean lifetime mortality risk due to exposure of children to cardiac intervention can be found using the following formula:
x s
ð1Þ E (mSv)
E ¼ 9:26 kgm Sv Gy1 cm2 DAP=BW
Range
7.45 kg mSv Gy1 and 11.07 kg mSv Gy1 for the posterioranterior and lateral projections, respectively. Given that the viewing direction changes during most procedures and the DAP is logged by our biplane angiographic system only as a sum from both planes, we used an average conversion factor to estimate E:
3.59 10.41 2.72 3.90 2.64
869 Median
Song et al.
870
Acta Radiologica 56(7) Table 3. Comparison between effective dose for therapeutic pediatric cardiac intervention reported in this work and by others. E in this study
E by Yakoumaks (12)
E by El Sayed (13)
Procedure
Mean
3rd quartile
Mean
3rd quartile
Mean
PDA closure VSD closure ASD closure PBPV total
10.3 11.9 5.1 3.6 8.7
11.3 16.5 4.1 3.9 11.3
4.9 6.0 6.3 3.0 5.0
6.8 4.6 7.7 3.2 5.9
6.5 3.3 2.9 6.0
ASD, atrial septal defect; E, effective dose; PBPV, percutaneous balloon pulmonary valvuloplasty; PDA, patent ductus arteriosus; VSD, ventricular septal defect.
was in the range of 0.02–1.02 Gy. The highest PSD was 1.02 Gy for the same patient. One patient who underwent RF ablation had a PSD greater than 1 Gy. Table 2 also summarizes the DAP measurements and E calculations. The mean doses together with the minimum and maximum dose values were tabulated. For all cases, the DAP range was found to be 1.29–90.0 Gy cm2. The corresponding E was (8.7 9.7 mSv), which is higher than the data obtained by Yakoumakis et al. (12) (5.0 4.7 mSv) and by El Sayed et al. (13) (5.97 7.05 mSv) for patients undergoing therapeutic procedures. The E varied widely among the procedures and individual cases in the range of 0.44–66.7 mSv. The highest E for an interventional procedure was calculated for a 2.3-year-old boy weighing 12.5 kg who underwent a PDA closure. The lowest E for an interventional procedure was calculated for a 15-year-old girl weighing 38 kg who underwent RF ablation. One patient that underwent a PDA had a PSD greater than 1 Gy. The third quartile (75th percentile) is often used to establish a reference level (RL) (14,15). We used the third quartile of the distribution of E for all procedures and then compared some of them with data from the literature (12,13). It is apparent from Table 3 that our values for E exceeded those in Yakoumakis’s study in the PDA and VSD closure procedures. The risk value was obtained using E and the risk factor based on the patient’s age. Generally, the risk was 1.16 per thousand. The relationship between two dosimetry characteristics of PSD and DAP was evaluated for all 90 cases. Good correlation was found between PSD and DAP (Pearson r ¼ 0.70; P < 0.01, two-tailed t-test) (Fig. 1). Linear regression yielded a formula for estimation of PSD from DAP: PSD (cGy) ¼ 3.33 þ 0.53 DAP (Gy cm2). However, correlation in individual cases was poor.
Discussion Patient radiation exposure during cardiac catheterizations is relatively high compared to other procedures
Fig. 1. Scatter-plot of DAP and PSD for 90 cases of therapeutic cardiac intervention procedures. The regression line is shown.
involving ionizing radiation. A child receiving a high dose of ionizing radiation has many years for the potential development of malignancies associated with X-ray radiation. Patient radiation dose data should be monitored and recorded for all procedures that are known to be associated with relatively high patient radiation doses (16,17). This study was designed and intended to provide data on ‘‘real-world’’ doses for five cardiac interventional therapy procedures, with no attempt to standardize either the technical factors for each fluoroscopic unit or the way in which each procedure was performed. The dose data in this study represent current practice in our hospital. Generally, there was a wide variation in the doses between the different procedures. Significant differences were observed in time and DAP among the five groups. This was expected because there was no standard technique with which to perform a cardiac catheterization. The radiographic factors and acquisition data depend strongly on the patient’s characteristics and corresponding complexity of the congenital disease.
Downloaded from acr.sagepub.com at Yale University Library on July 4, 2015
Song et al.
871
Table 4. Comparison between DAP/BW for therapeutic pediatric cardiac intervention reported in this work and by others. DAP/BW (Gy cm2 kg–1) in this study
DAP/BW (Gy cm2 kg–1) by Onnasch et al. (28)
Procedure
n
Mean
3rd quartile
n
Mean
3rd quartile
PDA closure VSD closure ASD closure Total
20 22 17 90
0.618 0.803 0.331 0.867
0.363 1.073 0.367 1.091
165 32 259 883
0.347 1.303 0.419 0.559
0.368 1.755 0.500 0.656
ASD, atrial septal defect; BW, body weight; DAP, dose-area product; PDA, patent ductus arteriosus; VSD, ventricular septal defects.
All of the cases we evaluated were radiated with a PSD
