Donovan M. Bakalyar PhD, Presenter: Nothing to Disclose

Erin Angel PhD, Abstract Co-Author: Employee, Toshiba Corporation

John M. Boone PhD, Abstract Co-Author: Research Grant, Siemens AG Research Grant, Hologic, Inc Consultant, Varian Medical Systems, Inc

Heather Chen-Mayer PhD, Abstract Co-Author: Nothing to Disclose

Dianna D. Cody PhD, Abstract Co-Author: In-kind support, General Electric Company

Wenzheng Feng BMBCh, Abstract Co-Author: Nothing to Disclose

Iacovos Kyprianou PhD, Abstract Co-Author: Nothing to Disclose

Shuai Leng PhD, Abstract Co-Author: Nothing to Disclose

Sarah Eva McKenney PhD, Abstract Co-Author: Nothing to Disclose

Michael F. McNitt-Gray PhD, Abstract Co-Author: Institutional research agreement, Siemens AG Research support, Siemens AG

Richard L. Morin PhD, Abstract Co-Author: Nothing to Disclose

J. Thomas Payne PhD, Abstract Co-Author: Nothing to Disclose

Robert J. Pizzutiello MD, Abstract Co-Author: Consultant, Matakina Technology Limited

Jeffrey H. Siewerdsen PhD, Abstract Co-Author: Research Grant, Siemens AG Consultant, Siemens AG Research Grant, Carestream Health, Inc Royalties, Elekta AB

Keith J. Strauss MS, Abstract Co-Author: Research Consultant, Koninklijke Philips NV Speakers Bureau, Koninklijke Philips NV

Paul B. Sunde, Abstract Co-Author: Shareholder, Radcal Corp Employee, Radcal Corp

Thomas Louis Toth, Abstract Co-Author: Co-founder, Plexar Imaging, Inc

Designed to incorporate the approaches described in TG111, the AAPM-ICRU phantom provides the means to standardize and unify dose measurements on a wide variety of CT scanners including diagnostic scanners with extended beams, cone beam and flat panel geometries.

The phantom and measurement techniques used to obtain CTDIvol and DLP have limitations that can impose challenges in obtaining equivalent measurements on the growing number of cone beam and very wide fan beam CT machines. In accordance with the recommendations of AAPM Task Group 111 (TG111), TG200 has designed a phantom and tested procedures which are suitable over a broader range of machines than the current methodology. The phantom design and measurement methods lend themselves to a more unifying set of dose descriptors, especially when the concept of irradiated length is employed.

The phantom is 30 cm in diameter and is constructed of polyethylene; it is of sufficient length (60 cm) so that scatter reaching the central plane from the ends of the phantom is negligible. For scanners with a moving table, a small detector is placed within the central plane and a helical scan through the entire phantom is performed. The dose recorded by the chamber approaches Deq, the value that would be reached for an infinite scan. By recording the dose rate simultaneously, dD(L)/dL can be determined, where D(L) is the dose as a function of the irradiated length L. Integrating this gives us the approach to equilibrium function H(L) = D(L)/Deq. By employing the principle of irradiated length, these concepts can be extended to axial scans on stationary tables. These phantoms have been tested at a variety of locations either with the assistance of a member of TG200 or “cold” using written instructions only.

H(L) is a robust function with only a weak dependence on tube potential, z-axis collimation and even scanner model. The phantom design is easily adaptable to the size specific dose estimates described by the report of AAPM Task Group 204 resulting in an index that remains simple but accounts for both girth and scan length. Correlations to air and small phantom measurements can be used for verification in the field.

Bakalyar, D, Angel, E, Boone, J, Chen-Mayer, H, Cody, D, Feng, W, Kyprianou, I, Leng, S, McKenney, S, McNitt-Gray, M, Morin, R, Payne, J, Pizzutiello, R, Siewerdsen, J, Strauss, K, Sunde, P, Toth, T, The AAPM-ICRU CT Dose Phantom: A Robust and Versatile Tool for Dose Measurements Across CT Platforms.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14008183.html