Method of patient dose evaluation in the angiographic and interventional radiology procedures.

Purpose: The aim of this study was to evaluate the effective dose in interventional radiology and angiography procedures on the basis of the dose-area product (DAP), either measured or calculated using two different methods.

Materials And Methods: We studied 2072 examinations carried out on several X-ray systems both in angiography and in interventional radiology. Some of the systems were equipped with an on-board transmission chamber for DAP measurements; for these systems we took direct DAP measurements for each type of examination. For the systems without the dose measurement device, we used a portable transmission chamber, acquiring the data from a set of sampling frames. We then derived the dose values from the systems' dosimetry data and the information about each examination. To this end, the dosimetry of each x-ray system was done by measuring tube output in the different acquisition modes, backscatter factor and field-homogeneity factor. Survey data sheets were filled in after every examination indicating the exposure data (mean Kv, mAs, focus-skin distance and field size). These values combined with the dosimetric data were used to evaluate the DAP for each exam. Where possible, we compared the measured and calculated DAP values by assessing the percentage deviation between each pair of values. A similar comparison was made for the single examinations using a simplified calculation algorithm reported in the literature. For all the examinations for which we had adequate survey data sheets, we estimated the DAP and the entrance dose values and, with the aid of WinODS software, the effective dose.

Results: The direct measurements of DAP showed that, in interventional radiology and angiographic procedures, the variability in examination conditions leads to a wide range of possible patient doses even within the same examination type. The comparison between the measured and calculated DAP using our algorithm showed substantial agreement (mean difference 30%, maximum 80%). By contrast, using the algorithm proposed in the literature, we obtained deviations higher than 100%. An estimate of the effective dose for all the recorded examinations (2072) permitted evaluation of both magnitude and variability of patient doses in special radiology procedures such as angiography and interventional radiology. However, it should be noted that evaluations based on calculated DAP values may be as uncertain as those estimated for DAP, and that clearly the evaluations made for the examinations for which direct measurements are available are more accurate. In particularly ''invasive'' examinations in terms of entrance dose, where the threshold limits for deterministic effects might possibly be exceeded, the equivalent doses to critical organs were also assessed. This analysis showed that in a small percentage of patients (5%) 2 Gy to the skin was exceeded in the areas exposed with possible transient erythema, while in fewer than 2% of patients, the 3 Gy limit for temporary epilation was exceeded.

Conclusions: Many interventional radiology, especially haemodynamic, examinations have shown to give significant exposure to patients. The direct dose measurement method has shown to be the only method able to provide reliable information on such exposure.However, the authors believe that since the patient dose cannot be established in advance, even in terms of magnitude and since direct dose measurement cannot be performed on all patients, it is nonetheless interesting to be able to assess, at least semiqualitatively, the amount of the above doses.