Estimation of Organ and Effective Doses for Neonate and Infant Diagnostic Cardiac Catheterizations

Medical Physics and Informatics Original Research Kawasaki et al. Dose Estimates for Neonate and Infant Diagnostic Cardiac Catheterization Medical Physics and Informatics Original Research Toshio Kawasaki 1 Keisuke Fujii 2 Keiichi Akahane 3 Kawasaki T, Fujii K, Akahane K Keywords: anthropomorphic phantoms, diagnostic cardiac catheterization, effective dose, organ dose, pediatrics DOI:10.22/AJR..13852 Received September 25, 20; accepted after revision March 23, 2015. 1 Department of Radiological Technology, Kanagawa Children s Medical Center, 2-138-4 Mutsukawa, Minami-ku, Yokohama 232-8555, Japan. Address correspondence to T. Kawasaki (kawasakipencil@yahoo.co.jp). 2 School of Health Sciences, Nagoya University, Nagoya, Japan. 3 Medical Exposure Research Promotion Section, National Institute of Radiological Sciences, Chiba, Japan. AJR 2015; 205:599 603 0361 803X/15/2053 599 American Roentgen Ray Society Estimation of Organ and Effective Doses for Neonate and Infant Diagnostic Cardiac Catheterizations OBJECTIVE. Radiation exposure to neonates and infants during cardiac catheterizations is an important issue. Smaller patient size and higher heart rate in these patients result in a greater need for magnification modes and higher frame rates, all of which contribute to a significant increase in radiation doses. The aims of our study were to evaluate organ and effective doses for neonates and infants during diagnostic cardiac catheterizations on the basis of in-phantom dosimetry and conversion factors from dose-area product (DAP) to the effective dose. MATERIALS AND METHODS. Organ doses for 0- and 1-year-old children during diagnostic cardiac catheterizations were measured by radiophotoluminescence glass dosimeters implanted in neonate and infant anthropomorphic phantoms. The effective doses were evaluated according to recommendations of the International Commission on Radiologic Protection (ICRP) publication 103. RESULTS. The mean effective doses evaluated according to ICRP 103 were 7.7 msv (range, 0.1 18.4 msv) for a neonate and 7.3 msv (range, 1.9 18.6 msv) for an infant. Conversion factors from DAP to the effective dose were 2.2 and 4.0 in posteroanterior and lateral cine angiography, respectively, for a neonate and 1.4 and 2.7 in posteroanterior and lateral cine angiography, respectively, for an infant. CONCLUSION. The dose data and conversion factors evaluated in this study could be useful for the estimation of radiation exposure in neonates and infants during diagnostic cardiac catheterization. A lthough echocardiography and MRI have played increasingly important roles in the evaluation of pediatric congenital heart disease, cardiac catheterization still possesses unique attributes that other imaging modalities have yet to match or exceed [1]. Radiation exposure issues for neonates and infants during cardiac catheterization are particularly relevant. Smaller patient size and higher heart rate result in a greater need for magnification modes and higher frame rates, all of which may contribute to a significant increase in radiation dose. Furthermore, pediatric patients with complex cardiac anomalies are at greater risk of radiation exposure because of the need for frequent cardiac catheterizations during childhood [1]. Most of the radiation dosimetry studies of pediatric cardiac catheterization have been performed using measurements with thermoluminescence dosimeters to estimate the dose to the skin, thyroid, and gonads [2 6]. Other studies have assessed effective doses using Monte Carlo simulation [7, 8]. However, detailed data on absorbed doses at various organs or tissues for neonates and infants during diagnostic cardiac catheterizations, determined using an anthropomorphic phantom, have seldom been reported. The aims of this study were to evaluate organ and effective doses in neonate and infant diagnostic cardiac catheterizations based on in-phantom dosimetry and conversion factors from dose-area product (DAP) to the effective dose. Materials and Methods Parameters to evaluate radiation dose were investigated and determined from clinical studies and then were used for the phantom work. In-Phantom Dosimetry System The dosimeter system used in this study was the radiophotoluminescence glass dosimeter system. The radiophotoluminescence glass dosimeter system (Dose Ace, Asahi Techno Glass) consists of silver-activated phosphate glass dosimeters and an automatic readout system (FGD-1000, Asahi AJR:205, September 2015 599

Kawasaki et al. Techno Glass). Radiophotoluminescence glass dosimeters were annealed at 400 C for 30 minutes, and the initial values were read using the automatic readout system. After x-ray beam irradiation, radiophotoluminescence glass dosimeters were heated at 70 C for 30 minutes and were again read using the automatic readout system. The radiophotoluminescence glass dosimeter has two types of dosimeters: one without an energy compensation filter (GD-302 M, Asahi Techno Glass) and one with a tin filter for adjusting photon energy dependence (GD-352 M, Asahi Techno Glass). The construction details and characteristics of the dosimeters have been fully described by Nishizawa et al. [9]. Use of the GD-352 M filter was recommended for the x-ray energy range of diagnostic interest because its energy dependence response is almost flat, from 45 to 60 kev (the range commonly used in neonate and infant diagnostic cardiac catheterizations), and the response of the GD-302 M was estimated to be 20%, from 45 to 60 kev [9]. Thus, the GD-352 M was mainly used for dose measurement in the pediatric cardiac catheterizations with neonate and infant phantoms, and the GD-302 M was alternatively used for dose measurement at positions where the GD-352 M was too large to set in the neonate and infant phantoms. Radiation doses were measured with pediatric anthropomorphic phantoms (ATOM model 703- C for neonates and model 704-C for infants, both from CIRS), which are shown in Figures 1 and 2. The phantoms represent the average body size of 0-year-old neonate (weight, 3.5 kg; height, 51 cm) and a 1-year-old infant (weight, 10 kg; height, 75 cm), respectively. These body sizes are similar to those of standard Japanese 0- and 1-year-old children, respectively. The phantoms are composed of tissue-equivalent substitutes corresponding to soft tissue, lung, and bone, and are divided into 25-mm-thick axial slices. Each slice contains a matrix of holes 5 mm in diameter to enable the setting of dosimeters. The holes were filled with tissue-equivalent plugs when they were not used. In total, 104 radiophotoluminescence glass dosimeters for the neonate phantom and 9 radiophotoluminescence glass dosimeters for the infant phantom were set at the positions of tissues or organs for which tissue-weighting factors were provided by the International Commission on Radiologic Protection (ICRP) [10]. The radiophotoluminescence glass dosimeters were calibrated to the Japanese national standard, by use of a traceable ionization chamber, at the National Institute of Advanced Industrial Science and Technology (Tokyo, Japan). We set radiophotoluminescence glass dosimeters and the ionization chamber in or on a soft tissue equivalent slab phantom and irradiated the phantom with x-ray beams of various energies. The readout values of radiophotoluminescence glass dosimeters were converted into absorbed doses for tissues or organs using the conversion factors obtained from the calibration. Doses for red bone marrow and the bone surface were evaluated from the doses measured in various bone tissues and weight fractions of the red bone marrow and mineralized bone for 0-year-old neonates and 1-year-old infants, as given in ICRP publication 70 [11]. Doses for skin were evaluated from the radiophotoluminescence glass dosimeters attached to the surface of the phantom in a direct x-ray beam; the ratio of the irradiated area to the gross surface was 0.20 m 2 for a neonate phantom and 0.37 m 2 for an infant phantom. Doses for the remaining organs were evaluated as the average doses for the following 11 organs: adrenal glands, extrathoracic region, gallbladder, heart, kidneys, oral mucosa, pancreas, prostate (male patients), small intestine, spleen, thymus, and uterus or cervix (female patients), which were selected from the remainder assigned in ICRP publication 103 [10]. To compare the present dose levels with those in the literature, the effective doses were evaluated according to the values given in both ICRP publication 103 and ICRP publication 60 [12]. Technical Parameters in Fluoroscopy and Cine Angiography All dose measurements were performed with a biplane x-ray system (Integris Allura 9, Philips Healthcare). This unit consists of two pairs of an undercouch x-ray tube and an overcouch image intensifier. The image intensifier unit has an antiscatter grid with a ratio of 10:1 and three magnification modes of 23, 18, and cm. The image intensifier field size used was cm for the neonate phantom and 18 cm for the infant phantom. The distances between the source and the image intensifier were 90 cm for the posteroanterior view and 110 cm for the lateral view. The pulsed rate in fluoroscopy was 7.5 pulses/s, and the frame rate in cine angiography was 30 frames/s. The x-ray tube was equipped with total filtration of 4 mm in equivalent aluminum for fluoroscopy and cine angiography. Dose measurements were performed using technical parameters, such as tube voltage, tube current, and filtration, that are routinely used in pediatric diagnostic cardiac catheterizations. The technical parameters are shown in Tables 1 and 2. DAPs for fluoroscopy and cine angiography were measured with a DAP meter (KermaX plus model 120 132, Scanditronix) built into the x-ray unit, where a flat ionization chamber was attached to the collimator of each x-ray tube. The integrated DAP meter is checked twice a year against a reference DAP meter (Xi model 8201010-A, with a probe model 82020030-AXi, both from Unfors Instruments). Conversion factors from DAP to the Fig. 1 Pediatric anthropomorphic phantom for neonates (ATOM model 703-C, CIRS). Fig. 2 Pediatric anthropomorphic phantom for infants (ATOM model 704-C, CIRS). 600 AJR:205, September 2015

effective dose were evaluated by using measured TABLE 1: Mean Organ Doses and Effective Doses for Neonates During Diagnostic Dose Estimates for Neonate and Infant Diagnostic Cardiac Catheterization DAPs for neonate and infant phantoms and measured Cardiac Catheterization, by Imaging Parameter and Procedure effective doses based on phantom dosimetry. Diagnostic cardiac catheterizations for 264 Cine Lateral Cine children, 0 15 years old, were performed between Imaging Parameter Fluoroscopy Angiography Angiography Total April 1, 2009, and March 31, 2010, at Kanagawa Children s Medical Center. Approximately 30% and 25% of the examinations were of 0-year-old neonates and 1-year-old infants, respectively. We Tube potential (kv) Tube current (ma) Effective energy (kev) 69 4 52.5 70 216 47.5 72 254 48.2 investigated mean fluoroscopic and cine angiographic times for the 6 neonates and infants. The Half-value layer (mm Al) 7.6 6.4 6.6 Added filtration (mm) 1 mm Al + 1 mm Al + 1 mm Al + beam projection angle in fluoroscopy was almost a 0.9 mm Cu 0.4 mm Cu 0.4 mm Cu posteroanterior view, and in cine angiography, the views were posteroanterior and lateral. Mean fluoroscopic Time (ms) 3 3 and cine angiographic times and mean No. of pulses/s 7.5 numbers of frames in cine angiography during diagnostic cardiac catheterizations are summarized in Table 1 for neonates and in Table 2 for infants. We measured entrance skin doses, organ doses, and DAPs for 60 seconds during fluoroscopy and for 10 seconds during cine angiography, which corresponds to 300 frames. Each radiophotoluminescence No. of frames/s No. of cineangiography procedures Mean fluoroscopic or cineangiographic time (s) Image intensifier field size (cm) Distance between source and image intensifier (cm) 39 90 30 1082.1 36.1 90 30 1051.8 35.1 110 glass dosimeter was irradiated only one Focus-to-skin distance (cm) 72 72 72.3 time per one irradiated condition. Dose measurements were not repeated. We evaluated the dos- ) 84 84 55 Field size on skin (cm es in mean fluoroscopic or cine angiographic time for neonates and infants during diagnostic cardiac Organ dose (mgy), by tissue or organ Brain 0.4 0.2 0.1 0.7 catheterizations from the measured doses per unit Lens 0.3 0.1 0.1 0.5 time. Dose measurements for posteroanterior and lateral projections are shown in Tables 1 and 2. Salivary gland 0.9 0.4 0.3 1.6 Thyroid gland 7.9 3.4 2.4 13.7 Results Mean values for organ doses, effective doses, DAP, and conversion factors for neonates and infants during diagnostic cardiac catheterization procedures are summarized in Tables 1 and 2. For neonates, fluoroscopic times were 36 3186 seconds and cine angiographic times were 0 90.4 seconds for both posteroanterior and lateral projections during the diagnostic cardiac catheterizations. For infants, fluoroscopic times were 450 5022 seconds and cine angiographic times were 8.1 66.9 seconds for posteroanterior and lateral projections during the diagnostic cardiac catheterizations. The total doses for organs, such as lung, esophagus, and breast, irradiated by primary x-ray beam were approximately 16.9 21.6 mgy for both neonates and infants (Tables 1 and 2). The breast doses for neonates during cine angiography were 2.8 mgy for the posteroanterior view and 7.1 mgy for the lateral view (Table 1). The breast doses for infants during cine angiography were 4.0 mgy for the posteroanterior view and 7.5 mgy for the lateral view (Table 2). According to ICRP publication 103 [10], the total effective doses in fluoroscopy and cine angiography are 7.7 msv for neonates and 7.3 msv for infants. In our study, the Lung 9.7 4.2 5.9 19.7 Esophagus 10.6 4.2 6.7 21.6 Breast 7.0 2.8 7.1 16.9 Liver 1.6 0.6 1.3 3.6 Stomach 1.4 0.5 0.8 2.7 Colon 0.4 0.1 0.2 0.7 Ovary 0.3 0.1 0.1 0.4 Bladder 0.2 0.0 0.1 0.3 Testis 0.1 0.0 0.0 0.1 Maximum skin 16.8 6.8 11.9 35.5 Skin 1.1 0.5 0.8 2.4 Red bone marrow 2.9 1.2 1.1 5.3 Bone surface 6.8 3.4 3.0 13.1 Other new organ, male or female, according 1.9 0.7 1.6 4.2 to ICRP 103 Other new organ male or female, according 1.6 0.6 1.2 3.4 to ICRP 60 Mean effective dose (msv) according to ICRP 3.7 1.5 2.5 7.7 103 Mean effective dose (msv) according to ICRP 3.3 1.4 1.9 6.6 60 Dose-area product (Gy cm 2 ) 1.6 0.7 0.6 2.9 Conversion factor from dose-area product to effective dose, ICRP 103 2.34 2.2 4.0 Note ICRP 103 = International Commission on Radiological Protection publication 103 [10], ICRP 60 = International Commission on Radiological Protection publication 60 [12]. AJR:205, September 2015 601

TABLE 2: Mean Organ Doses and Effective Doses for Infants During Diagnostic Kawasaki et al. Cardiac Catheterization, by Imaging Parameter and Procedure Imaging Parameter Fluoroscopy Cine Angiography Lateral Cine Angiography Tube potential (kv) 70 73 72 Tube current (ma) 4.3 266 266 Effective energy (kev) 52.9 48.6 48.2 Half-value layer (mm Al) 7.7 6.7 6.6 Additional filter 1 mm Al + 0.9 mm Cu 1 mm Al + 0.4 mm Cu 1 mm Al + 0.4 mm Cu Time (ms) 3 3 No. of pulses/s 7.5 No. of frames/s 30 30 No. of cineangiography procedures 1178.7 1122.3 Mean fluoroscopic or cineangiographic time (s) 1361 39.3 37.4 Image intensifier field size (cm) 18 18 18 Distance between source and image 90 90 110 intensifier (cm) Focus-to-skin distance (cm) 71 71 71.5 Field size on skin (cm 2 ) 108 108 74 Organ dose (mgy), by tissue or organ Brain 0.2 0.1 0.0 0.3 Lens 0.1 0.0 0.0 0.2 Salivary gland 0.5 0.2 0.2 0.9 Thyroid gland 5.3 2.6 1.8 9.7 Lung 9.5 6.2 5.3 21.1 Esophagus 7.2 5.0 5.5 17.7 Breast 6.4 4.0 7.5 17.9 Liver 1.0 1.0 0.7 2.7 Stomach 1.0 0.9 0.5 2.4 Colon 0.1 0.1 0.1 0.3 Ovary 0.1 0.0 0.0 0.1 Bladder 0.0 0.0 0.0 0.1 Testis 0.0 0.0 0.0 0.0 Maximum skin 19.8 13.8 13.6 47.3 Skin 0.6 0.4 0.5 1.5 Red bone marrow 2.0 1.2 0.9 4.1 Bone surface 4.5 3.3 3.2 10.9 Other new organ, male or female, according 1.3 0.9 1.4 3.6 to ICRP 103 Other new organ, male or female, according 0.8 0.6 1.1 2.6 to ICRP 60 Mean effective dose (msv) according to ICRP 3.0 2.0 2.3 7.3 103 Mean effective dose (msv) according to ICRP 2.6 1.7 1.7 6.0 60 Dose-area product (Gy cm 2 ) 2.4 1.4 0.8 4.6 Conversion factor from dose-area product to effective dose, ICRP 103 1.27 1.4 2.7 Note ICRP 103 = International Commission on Radiological Protection publication 103 [10], ICRP 60 = International Commission on Radiological Protection publication 60 [12]. Total range of total effective doses was 0.1 18.4 msv for neonates and 1.9 18.6 msv for infants. Cine angiography contributed approximately 50 60% of the total effective doses for both neonates and infants. Maximum entrance doses on the patient s back for the posteroanterior view during cardiac catheterization procedures were estimated to be 23.6 mgy for neonates and 33.7 mgy for infants. The range was 0.4 54.2 mgy for neonates and 9.4 96.7 mgy for infants. The maximum entrance doses on the patient s lateral side for the lateral view were 11.9 mgy for neonates and 13.6 mgy for infants. The range was 0 30.7 mgy for neonates and 2.9 24.3 mgy for infants. The conversion factors from DAP to the effective dose were 2.2 and 4.0 for posteroanterior and lateral cine angiography, respectively, for neonates and 1.4 and 2.7 in posteroanterior and lateral cine angiography, respectively, for infants. Discussion The breast dose in the lateral projection was the highest of any organ dose within the irradiated range for neonates and infants. Fujii et al. [13] assessed lung, esophagus, and breast doses in 1-year-old infants during cardiac CT examination and found values of 3.8 13.5 mgy. This implies that the cancer risk for organs in the chest region during neonate and infant diagnostic cardiac catheterizations is almost two to five times higher than the risk during infant cardiac CT examination. Because maximum peak skin doses are less than 100 mgy and far less than a threshold dose of 2 Gy for the onset of skin injury [], radiation dermatitis would not be induced in neonate and infant cardiac catheterization examinations. In our study, effective doses per time for the lateral view in cine angiography were 1.7 and 1.2 times higher than those for the posteroanterior view in neonates and infants, respectively. This is partly because breast doses per time for the lateral view in cine angiography were approximately two to three times higher than those for the posteroanterior view in cine angiography. The breast was positioned at the front surface of the phantom and one of the organs with the highest tissueweighting factor. For reduction of the effective dose, one of the more effective methods would be to reduce cine angiographic times and the number of lateral views in cine angiography. Additionally, shielding the anterior and posterior part of patients in lateral view cine angiography and reducing direct x-ray to the breast might efficiently reduce breast and effective doses. Although the unit used in this study was not capable of shielding 602 AJR:205, September 2015

Dose Estimates for Neonate and Infant Diagnostic Cardiac Catheterization obliquely along the chest wall, this intervention could reduce breast and effective doses while maintaining diagnostic quality. The current study did not reveal a statistically significant difference in mean effective doses between the neonate and infant groups because mean fluoroscopic time, mean cine angiography time, and the measured effective dose per second in fluoroscopy and cine angiography were similar. The conversion factors estimated using neonate and infant anthropomorphic phantoms in the present work were 2.2 and 4.0 in posteroanterior and lateral cine angiography, respectively, for neonates. These values are similar to the values of 3.65 and 3.74 calculated by Karambatsakidou et al. using Monte Carlo simulation [15]. One reason that the x-ray qualities were similar in both studies is because the manufacturer and additional copper filter of the units used were the same. Betsou et al. [16] assessed effective doses in adult coronary angiography and percutaneous transluminal coronary angioplasty and found mean values of 5.6 and 6.9 msv, respectively. Effective doses for neonates and infants in diagnostic cardiac catheterizations are slightly higher than those for adult coronary angiography and percutaneous transluminal coronary angioplasty [16]. Because neonates and infants have higher radiosensitivities, the higher doses they receive would result in a higher risk than for adults. The increased dose that is associated with a smaller FOV for an intensified image may not be a significant factor in all situations when a flat-panel digital detector is used. Therefore, the effect of this parameter remains to be examined. Jones et al. [17] assessed an effective dose of 15.4 µsv for newborns in chest radiographic examination. The effective doses for neonates in diagnostic cardiac catheterization were 500 higher times than those for a neonatal chest radiographic examination [17]. Fujii et al. [13] assessed effective doses of 1.4 6.3 msv for infants in cardiac CT examination, and Neshandar Asli and Tabeie [18] assessed effective doses of 1.9 2.8mSv in pediatric mean lung perfusion scintigraphy. The effective doses for infants per examination in diagnostic cardiac catheterizations were higher than those in other cardiac imaging modalities. Neonates and infants with congenital heart disease need to undergo multiple diagnostic cardiac catheterizations [7]. Therefore, radiation doses during diagnostic cardiac catheterization present a higher risk for children with congenital heart disease. Conclusion We evaluated organ doses and effective dose in diagnostic cardiac catheterization using neonate and infant anthropomorphic phantoms. The mean effective doses evaluated according to ICRP publication 103 [10] were 7.7 msv (range, 0.1 18.4 msv) for a neonate and 7.3 msv (range, 1.9 18.6 msv) for an infant; these were higher than those of other cardiac imaging modalities. Conversion factors from DAP to the effective dose were 2.2 and 4.0 in posteroanterior and lateral cine angiography, respectively, for neonates and 1.4 and 2.7 in posteroanterior and lateral cine angiography, respectively, for infants. The dose data and conversion factors evaluated in this study could be useful for the estimation of radiation risks for neonates and infants in diagnostic cardiac catheterization. References 1. Justino H. The ALARA concept in pediatric cardiac catheterization: techniques and tactics for managing radiation dose. Pediatr Radiol 2006; 36:6 153 2. Boothroyd A, McDonald E, Moores BM, Sluming V, Carty H. Radiation exposure to children during cardiac catheterization. Br J Radiol 1997; 70:180 185 3. 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