Effective dose conversion factors in paediatric interventional cardiology

Conversion factors for effective dose (CF(E) = effective dose/dose-area product (mSv (Gy cm2)(-1)) in paediatric interventional cardiology were estimated retrospectively for 249 patients using the dose-area product (DAP), irradiation geometry, exposure parameters and tissue-weighting factors (TWFs) from the International Commission on Radiological Protection (ICRP) 60. Two methods for estimating the conversion factors, which differed in the description of the irradiation geometry, were evaluated. The effective doses obtained with the two methods were almost identical. The results showed that irradiation geometry had no significant impact on the CF(E), and a single factor was defined for both diagnostic and interventional examinations. In addition, the effect of the new tissue-weighting factor for breast tissue (TWF(b)) given in ICRP 103 on the effective dose was assessed. The CF(E) was 3.7+/-0.2 mSv (Gy cm2)(-1) (neonate), 1.9+/-0.2 mSv (Gy cm2)(-1) (1 year), 1.0+/-0.1 mSv (Gy cm2)(-1) (5 years), 0.6+/-0.1 mSv (Gy cm2)(-1) (10 years) and 0.4+/-0.1 mSv (Gy cm2)(-1) (15 years). Applying these CFs to the individual DAP values of each patient yielded mean effective doses of 13.0 mSv (neonate), 8.6 mSv (1 year), 6.4 mSv (5 years), 8.6 mSv (10 years) and 12.7 mSv (15 years). The maximum estimated skin dose (15 patients) did not exceed 60 mGy. With the new ICRP value for TWF(b), increases in the CFs in the order of 10-30%, and in the effective dose of 10-20%, were indicated. The results indicated that the effective dose in paediatric interventional cardiology is of much greater concern than the skin dose. Furthermore, age-dependent CF(E) values are required so as not to underestimate the doses to very young patients.