Effective and equivalent organ doses in patients undergoing coronary angiography and percutaneous coronary interventions

Abstract

Recent recommendations of the International Commission on Radiological Protection state that the use of effective dose (E) for assessing patient exposure has severe limitations, though it can be kept for dose comparisons. In cardiology procedures, the equivalent dose (H(T)) is one of the most appropriate dose quantity to be evaluated for risk-benefit assessment. In this study, both E and H(T) values for ten critical organs in coronary angiography (CA) and percutaneous coronary interventions (PCI) were derived from in-the-field dose-area-product (DAP) measurements in order to provide a database for doses in those procedures. Conversion factors E/DAP calculated by Monte Carlo methods in two different mathematical human phantoms were applied to DAP values measured on 193 patients (118 CA and 75 PCI). Partial DAP values were recorded in-the-field for each projection and for all patients. The partial effective doses of all projections were summed up to calculate the E of the entire procedure. Similarly, equivalent doses for ten critical organs/tissues (bone, colon, heart, liver, lung, esophagus, red bone marrow, skin, stomach, and thyroid) were derived from H(T)/DAP conversion factors for different projections calculated by Monte Carlo method. All parameters related to the patient dose, i.e., fluoroscopy times, number of images, DAP, effective doses, and equivalent doses, show a wide range of values depending on the complexity of the patient case and the experience of the cardiologist. The mean fluoroscopy time, DAP, and E values for coronary angiography patients were approximately threefold lower than those for PCI patients; the number of images for CA was half that for PCI. The correlation between effective dose and DAP was excellent for both CA and PCI. The equivalent doses values were in good correlations with DAP values in CA examinations, with Pearson's coefficients ranging from 0.87 (stomach) to 0.99 (skin) and r(mean) = 0.94. The same analysis was performed for PCI procedures. In this case, the trends were only slightly worse because "r" ranged from 0.70 (stomach) to 0.92 (bone) and r(mean) = 0.85. Simple conversion coefficients to estimate equivalent doses to ten critical organs/tissues from DAP values, for both CA and PCI, were provided for avoiding the need to carry out detailed in-the-field analysis for all projections and for all patients. Measurements in-the-field of DAP values were carried out for two common cardiology procedures and effective doses were derived for each technique from detailed analysis of dose and projection data, using conversion factors provided by two different theoretical models. Equivalent doses to organs/tissues were also calculated using conversion factors proposed in the literature for different projections and cumulative conversion factors (H)T/DAP for ten organs/tissues were estimated.