Embryo Dose Estimates in Body CT

作者：Huda Walter^*; Randazzo William; Tipnis Sameer; Frey G Donald; Mah Eugene

来源：American Journal of Roentgenology, 2010, 194(4): 874-880.

DOI：10.2214/AJR.09.4032

• CT radiation dose
• embryo dose
• patient size
• radiation protection
• x-ray techniques

OBJECTIVE. The purpose of this article is to develop a method for estimating embryo doses in CT.
MATERIALS AND METHODS. Absorbed doses to the uterus (embryo) of a 70-kg woman were estimated using the ImPACT CT Patient Dosimetry Calculator. For a particular CT scan length, relative uterus doses and normalized plateau uterus doses were determined for a range of commercial CT scanners. Patient size characteristics were obtained from cross-sectional axial images of 100 consecutive patients (healthy women undergoing unenhanced pelvic CT examinations). For each patient, the diameter of a water cylinder with the same mass as the patient's pelvis was computed. Relative dose values were generated for cylinder diameters ranging from 16 to 36 cm at x-ray tube voltages between 80 and 140 kV.
RESULTS. Values of relative uterus dose increased monotonically with increasing scan length, independently of scanner model, and reached a plateau for scan lengths greater than similar to 50 cm. The average normalized plateau uterus dose for all scanners was approximately 1.4 and showed inter-scanner differences of less than 10% for modern scanners operated at 120 kV. Normalized plateau doses show little dependence on the x-ray tube voltage used to perform the CT examination. Our results show that the uterus dose estimate in an abdominal or pelvis CT examination performed on a 70-kg patient is about 40% higher than the reported value of the volume CT dose index (CTDI(vol)). The pelvis of a 70-kg patient may be modeled as a water cylinder with a diameter of 28 cm and has an average anteroposterior dimension of 22 cm. For constant CT technique factors, embryo dose estimates for a 45-kg patient would be similar to 18% higher than those for a 70-kg patient, whereas the corresponding dose estimates in a 120-kg patient would be similar to 37% lower.
CONCLUSION. Embryo doses can be estimated using relative uterus doses, normalized plateau uterus doses, and CTDI(vol) data with correction factors for patient size.

• 出版日期2010-4