SU‐FF‐I‐34: How Well Do Ctdi Data Obtained in a Body Phantom Predict Patient and Embryo Doses in Abdominal Ct?

• Published in: Medical Physics 2006-06, Vol.33 (6), p.2004-2004
• Main Authors: Huda, W, Ogden, K, Boone, J, Nickoloff, E
• Format: Article
• Language: English
• Subjects: Computed tomography; Dosimetry; Image scanners; Ionization chambers; Tissues
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.2240273

Purpose: In this work, we compare central dose measurements in anthropomorphic phantoms with corresponding Computed Tomography Dose Index (CTDI) values obtained at the center of the body CTDI phantom. Method and Materials: An adult Rando phantom was used to determine patient/fetal dose during an abdominal/pelvic CT examination acquired with clinically relevant techniques. TLD's were placed in multiple locations in the phantom to measure the dose in the abdomen/pelvis region. The corresponding CTDIFDA and CTDI100 values were determined using an ionization chamber placed at the center of a 32 cm diameter acrylic dosimetry phantom. Results: A pregnant patient, whose size is comparable to the Rando phantom, undergoing a CT examination on a commercial scanner receives an embryo dose of 16 mGy/100mAs, whereas published CTDI values for this scanner are lower by factor of 2.9 to 4.0. This large discrepancy can be accounted for by the following three factors: (a) specification of a tissue dose, as opposed to an air or acrylic dose; (b) use of a realistic phantom size; (c) inclusion of the total x‐ray scatter in the tails of CT dose profiles. Conclusion: To obtain accurate body patient doses from any specified body CTDI data, it is essential that soft tissue doses be obtained rather than air/acrylic doses, and with appropriate correction factors that account for the scan length and for the size of the patient.