National Study of Radiation Exposures of Patients during X-ray Diagnostic Radiology Procedures in the Czech Republic Novak, L., Rada, J., Smejkal, O., Horakova, I., Oceansky, J. National Radiation Protection Institute, Prague

During the last few years, radiation exposures of patients have been studied for the following imaging modalities with the intention to establish national diagnostic reference levels (DRLs): chest photofluorography, , computed tomography, intraoral and panoramic , and interventional procedures involving X-rays. For each modality, relevant dosimetric quantities were selected in accordance with recent ICRU and IAEA recommendations.

For chest photofluorography examinations, the entrance surface air kerma, Ke> was selected as a relevant dosimetric quantity. It was measured with ionization chamber on a surface of a 30x30x10 cm3 water phantom corresponding to a standard sized patient (chest

region). A value of Ke was measured for 28 (from 33) X-ray facilities. The third quartile of the distribution of Ke was 10 mGy. For a standard chest general radiography examination in the Czech Republic, DRL is 0,4 mGy. Therefore, it was suggested to suppress further use of chest photofluorography in the country. y For mammography examinations, the mean glandular dose, D'G, for a cranio-caudal view was calculated from machine parameters measured during QC tests and parameters of the examinations obtained from patient's charts. The calculations followed a formalism suggested in EC recommendations. Calculations were made for 41 (from 138) machines (100 patients for each machine). Third quartiles were determined from distributions of Dg for different breast thickness. The measured values were compared with the European values. For computed tomography examinations, the weighted computed tomography kerma

index, Cvv, and the air-kerma length product, PKL, were used for patient dose assessment. These values were obtained from QC measurements and from data collection sheets describing the standard procedures for a given examination. The study focused on examination of a head (brain and face), abdomen, pelvis, thorax, lumbar spine.. Third

quartiles of Cw and Pkl distributions were determined and compared with current DRLs in the Czech Republic and Europe. For intraoral radiography, the incident air kerma, Kj, was used for DRL determination. Data were obtained by means of a postal audit. Measurement of Kj was made with TLDs for almost all machines (-3700) used in the Czech Republic. Third quartiles of K, distributions were determined for E speed films, D speed films and CCD sensors and compared with current Czech DRL. For panoramic radiography, no dose descriptor has been measured in the Czech Republic yet. The air kerma-length product, Pkl, measured at a secondary collimator was proposed as a relevant quantity. Pilot study was performed to determine a proper way of PKL measurement. At 8 machines, PKL measurement with a pencil ionization chamber, a stack of TLDs and a radiographic film were compared. The measurement using the ionization chamber is recommended. New DRLs were determined for mammography, computed tomography and intraoral radiography. In addition, the results of measurements for a chest photofluorography were used as a basis for an abandonment of this technique in radiology in the Czech Republic.