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On the Relationship of the Weighted Dose to the Surface Dose In Abdominal CT - Patient Size Dependency

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Y Zhou

Y Zhou1*, A Scott2 , J Allahverdian3 , (1) Cedars-Sinai Medical Center, Los Angeles, CA, (2) Cedars-Sinai Medical Center, Los Angeles, CA, (3) Cedars-Sinai Medical Center, Los Angeles, CA


SU-F-18C-12 Sunday 4:00PM - 6:00PM Room: 18C

Purpose: It is possible to measure the patient surface dose non-invasively using radiolucent dosimeters. However, the patient size specific weighted dose remains unknown. We attempted to study the weighted dose to surface dose relationship as the patient size varies in abdominal CT.

Methods: Seven abdomen phantoms (CIRS TE series) simulating patients from an infant to a large adult were used. Size specific doses were measured with a 100 mm CT chamber under axial scans using a Siemens Sensation 64 (mCT) and a GE 750 HD. The scanner settings were 120 kVp, 200 mAs with fully opened collimations. Additional kVps (80, 100, 140) were added depending on the phantom sizes. The ratios (r) of the weighted CT dose (Dw) to the surface dose (Ds) were related to the phantom size (L) defined as the diameter resulting the equivalent cross-sectional area.

Results: The Dw versus Ds ratio (r) was fitted to a linear relationship: r = 1.083 - 0.007L (R square = 0.995), and r = 1.064 - 0.007L (R square = 0.953), for Siemens Sensation 64 and GE 750 HD, respectively. The relationship appears to be independent of the scanner specifics.

Conclusion: The surface dose to the weighted dose ratio decreases linearly as the patient size increases. The result is independent of the scanner specifics. The result can be used to obtain in vivo CT dosimetry in abdominal CT.

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