Quality control and patient doses from X-ray examinations in some hospitals in Thailand

Quality control measurements on 203 diagnostic X-ray units were carried out in 126 hospitals in the central region of Thailand during 1998-2000. The measurements consisted of tube voltage, half-value layer (HVL), exposure time, radiation output, beam alignment, light beam diaphragm and entrance surface dose (ESD) in four common radiographic procedures, namely adult chest PA, adult mass chest PA in mobile bus unit, abdomen AP and mammography (cephalo caudal view). ESD measurements of 320 examinations were performed using parallel plate ionization chamber and Keithley model 35050A Dosimeter on 192 X-ray units (conventional and mobile) and 11 mammography units. The analysis of test results showed that: 1) 92% had X-ray tube voltage within the tolerance limit of 10% and HVL 3.03 mmAl ± 0.55 SD at 80 kVp measured; 2) 90% had exposure time within tolerance limit of 10%; 3) 86% and 98% had acceptable beam alignment and light beam diaphragm; 4) 95% had radiation output > 25 μGy at 1 m. for true 80 KVp; 5) It was found that the ESD values were adult chest (PA) varied from 0.18 mGy to 1.17 mGy (mean 0.2021 ± 0.2218 SD), adult mass chest (PA) varied from 0.043 mGy to 1.03 mGy (mean 0.2935 ± 0.2195 SD), abdomen (AP) varied from 0.302 mGy to 6.30 mGy (mean 2.177 ± 1.4818 SD), mammography (cephalo caudal view) varied from 3.49 mGy to 12.21 mGy (mean 7.788 ± 2.9896 SD). Further surveys are necessary and are being done to include measurements of image quality and for propagation of quality assurance activities in Thailand so as to reduce patient doses while maintaining the image quality. (author)