Scan region and organ doses in computed tomography

作者：He Wenjun^*; Marzolf Sean A; Tipnis Sameer; Huda Walter

来源：Radiation Protection Dosimetry, 2012, 148(4): 444-451.

DOI：10.1093/rpd/ncr200

The purpose of this study was to investigate how the choice of the scanned region affects organ doses in CT. ImPACT CT Patient Dosimetry Calculator (version 1.0) was used to compute absorbed doses to eight organs of interest in medical radiation dosimetry. For 13 dosimetry data sets, the authors calculated the maximum organ dose (D-max) as well as the corresponding organ dose for a scan with selected length D(L). These data permitted the relative dose (DrD(L)/D-max) to be determined for varying scan lengths. Computations were performed for a nominal X-ray tube current of 100 mA, a rotation time of 1 s and a CT pitch of 1. The authors also determined values of D-max/CTDIvol, where CTDIvol is obtained in a 32-cm diameter CT dosimetry phantom using the same radiographic techniques. For each organ, D-r was independent of the type of scanner, and increased monotonically to unity with increasing scan length. Relative doses for a scan restricted to the organ length ranged from 0.65 D-max for the bladder to 0.86 D-max for the lungs. There was good correlation (r0.64) between relative organ dose and the corresponding organ length. At 120 kV, the lowest value of D-max/CTDIvol was 1.23 for the breast and the highest was 2.22 for the thyroid. Varying the X-ray tube voltage between 100 and 130 kV results in changes in D-max/CTDIvol of no more than 4 . CT scans limited to the direct irradiation of an average-sized organ results in an absorbed dose of approximate to 0.75 D-max.

• 出版日期2012-3