Chun Ruan PhD, Presenter: Nothing to Disclose

Eduardo G. Yukihara PhD, Abstract Co-Author: Nothing to Disclose

William J Clouse, Abstract Co-Author: Nothing to Disclose

Patricia B. Rio Gasparian BS, Abstract Co-Author: Nothing to Disclose

Salahuddin Ahmad PhD, Abstract Co-Author: Nothing to Disclose

The CTDI has been the most commonly used parameter to estimate patient dose for single-slice CT, but may not be an accurate metric for multi-slice computed tomography (MSCT) due to the larger beam widths and the over beaming effect. This study was intended to evaluate the CTDI efficiency for MSCT and establish a set of correction factors to compensate the underestimation of current CTDI100 technology.

The MSCT dose profiles along z-axis (450 mm) were obtained by irradiating OSL strips placed inside an extended PMMA head and body phantom at different scan conditions by varying kVp settings and beam widths. The exposed strips were then read out using a custom built LED-based OSL reader and corrected with conversion factors. The CTDI100 was determined by integrating the area 50 mm on each side of dose profile center and the CTDI450 was similarly determined by integrating the area under the entire OSL dose profile. The CTDI efficiency can further be evaluated by calculating the ratio of CTDI100 and CTDI450.

By keeping the beam width constant, no considerable differences of CTDI efficiency as a function of tube voltages were observed. For the beam width of 40 mm, the average CTDI efficiency at the center of head and body phantom were 72.6% and 56.2%, respectively. The CTDI efficiency at the periphery of head and body phantom were 85.0% and 81.7% on average. By keeping the tube voltage constant, the CTDI efficiency was found to be independent of beam width along z axis. At the center of head phantom, the values ranged from 72.4% to 77.3%, and for the body phantom, the values ranged from 56.1% to 59.0%. The CTDI efficiency was found higher at the periphery than that at the center of phantoms. The head phantom data was found slightly higher than that of body phantom data.

CTDI100 measurement underestimates the CTDI∞ value even with 5 mm beam width. It was found that the CTDI efficiency did not significantly change as the beam width increases and tube voltage changes. A complete set of correction factor was developed to be used for accurate determination of CTDI∞ with the current available test equipments.

Combined with simple calibration, it gives this work great potential to be used not only in routine clinical quality assurance check but also a promising tool for accurate patient dose assessment.

Ruan, C, Yukihara, E, Clouse, W, Gasparian, P, Ahmad, S, Determination of Multislice CT Dose Index Efficiency Using Optically Stimulated Luminescence System.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9011136.html