Diagnostic reference levels and effective dose in paediatric cardiac catheterization

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Abstract
European states within the EEC are required to establish and use diagnostic reference levels (DRLs) in X-ray examinations. However, up to now there have been no DRLs for cardiac catheterization in children, nor as a rule is the effective dose estimated. We have evaluated the dose–area products (DAPs) for three different types of angiocardiography systems over a time span of 8 years. For each system DAP increased in proportion to the body weight (BW) over two orders of magnitude. The proportionality constant decreased over the years. To reduce the broad distribution of DAP the doses for cine acquisition (DAPA) and fluoroscopy (DAPF) were indexed with respect to the total numbers of acquired images (AN) and the total times of fluoroscopy (FT). DAPA/AN is directly proportional to BW with a high correlation (r = 0.896, n = 1346). Likewise, DAPF/FT is proportional to BW from 0.1 kg to 100 kg (r = 0.84, n = 2138). Therefore, by normalizing DAP to BW the growth dependent variation of DAP can be eliminated. There are numerous short examinations with very small total DAPs, which were separated from the group of diagnostic examinations. The mean DAP/BW of this group is 0.41 Gycm2 kg−1 (90th percentile: 0.81 Gycm2 kg−1, n = 1106). For interventional procedures in congenital heart diseases DAP/BW is significantly higher (p2 kg−1, 90th percentile: 1.16 Gycm2 kg−1, n = 883). There are significant differences between different types of interventional procedures, the mean values being between 0.35 Gycm2 kg−1 (occlusion of patent ductus botalli, n = 165) and 1.30 Gycm2 kg−1 (occlusion of ventricular septal defect, n = 32). For patients who are catheterized several times over the years, the cumulative effective dose (E) may reach high values, being especially high for patients with hypoplastic left heart syndrome (typically 11 mSv). E is derived from DAP/BW by use of a constant DAP/BW to E conversion factor, independent of the age of the patient. DAP/BW is appropriate to describe paediatric DRLs and is recommended instead of using mean DAP values for age groups.

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