Estimate of Radiation Doses in MDCT Using Patient Weight / 의학물리

The purpose of this study provides measurements of radiation dose from MDCT of head, chest, abdomen and pelvic examinations. A series of dose quantities that are measured of patient weight to compare the dose received during MDCT examinations. Data collected included: weight together with CT dose descriptors, volume CT dose index (CTDIvol) and dose length product (DLP). The effective dose was also estimated and served as collective dose estimation data. Data from 1,774 adult patients attending for a CT examination of the head (n=520) or chest (n=531) or abdomen (n=724) was obtained from spiral CT units using a same CT protocol. Mean values of CTDIvol was a range of 48.6 mGy for head and 6.9, 10.5 mGy for chest, abdomen examinations, respectively. And mean values of DLP was range of 1,604 mGy.cm for head, 250 mGy.cm for chest, 575 mGy.cm for abdomen examinations, respectively. Mean effective dose values for head, chest, abdominal CT were 3.6, 4.2, and 8.6 mSv, respectively. The degree of CTDIvol and DLP was a positive correlation with weight. And there was a positive correlation for weight versus CTDIvol (r2=0.62), DLP (r2=0.694) in chest. And head was also positive correlation with weight versus CTDIvol (r2=0.691), DLP (r2=0.741). We conclude that CTDIvol and DLP is an important determinant of weight within the CT examinations. The results for this study suggest that CT protocol should be tailored according to patient weight.

Comparison of Radiation Dose in the Measurement of MDCT Radiation Dose according to Correction of Temperatures and Pressure, and Calibration of Ionization Chamber / 의학물리

This study aims to conduct the comparative analysis of the radiation dose according to before and after the calibration of the ionization chamber used for measuring radiation dose in the MDCT, as well as of CTDIW according to temperature and pressure correction factors in the CT room. A comparative analysis was conducted based on the measured MDCT (GE light speed plus 4 slice, USA) data using head and body CT dosimetric phantom, and Model 2026C electrometer (RADICAL 2026C, USA) calibrated on March 21, 2007. As a result, the CTDIW value which reflected calibration factors, as well as correction factors of temperature and pressure, was found to be the range of 0.479~3.162 mGy in effective radiation dose than the uncorrected values. Also, under the routine abdomen routine CT image acquisition conditions used in reference hospitals, patient effective dose was measured to indicate the difference of the maximum of 0.7 mSv between before and after the application of such factors. These results imply that the calibration of the ion chamber, and the correction of temperature and pressure of the CT room are crucial in measuring and calculating patient effective dose. Thus, to measure patient radiation dose accurately, the detailed information should be made available regarding not only the temperature and pressure of the CT room, but also the humidity and recombination factor, characteristics of X-ray beam quality, exposure conditions, scan region, and so forth.