Donovan M. Bakalyar PhD, Presenter: Nothing to Disclose

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

CTDIvol as a function of position is neither the patient dose nor even the phantom dose. Nonetheless, when properly interpreted, it can be a valuable tool in the computation of organ dose using tools such as ImPACT, even in the presence of tube current modulation.

CTDIvol can be stored as an optional attribute with tag (0018,9345) in the DICOM metadata on an image by image basis. This attribute is described in the DICOM literature as the average dose associated with that image. Although this description is not correct, this parameter can still be very useful for dose computations, even in the presence of current modulation.

ImPACT is designed for the computation of dose with fixed scanning parameters and the start and end positions of the scan. However, CTDIvol, by itself, accounts for tube current, rotation time, pitch and collimation. (In general, variations in tube potential and scanner model only weakly affect the dose distribution.) Linearity along with the scan region dependency of ImPACT allows for the computation of dose in the presence of current modulation. Tabulation of CTDIvol as a function of position makes it unnecessary to know the collimation, tube current, rotation time and pitch in the computation of organ dose.

CTDIvol is obtained from the approximate spatial average of a 100 mm central portion of the single scan dose profile in the central plane of standard cylindrical phantoms. It is a function of collimation, pitch, tube potential, tube current, rotation time, and specific machine model. The reasoning in AAPM Task Group Report 111 along with published data shows that CTDIvol is directly proportional to the energy absorbed per rotation. Using ImPACT as a model and taking advantage of linearity, CTDIvol as a function of position can be used for the calculation of dose even in the presence of current modulation. Though ImPACT is limited to a standard, stylized patient, the principle should apply to any dose computation program where CTDIvol is computed.

Bakalyar, D, McKenney, S, CTDIvol per Slice: How It Should Be Interpreted and How It Can Be Used as an Aid in Computing Organ Dose in the Presence of Current Modulation.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14004076.html