AbstractID: 7895 Title: The Effect of Patient Size on CT Dosimetry
CT radiation dose is typically estimated based on measurements with the standard FDA
acrylic cylindrical CTDI phantoms. These phantoms are 15 cm long and are
manufactured in diameters of 32 cm and 16 cm, to simulate an adult abdomen and head.
The objective of this study is to more accurately estimate the radiation dose received by
different-sized adult and pediatric patients in abdominal CT. This is accomplished by
using a pencil ionization chamber to measure air kerma along the axis and at four
locations near the surface in five different abdominal phantoms. Each phantom is
anthropomorphically shaped, and made of tissue equivalent material, with a cylindrical
insert of bone equivalent material for the spine. The phantom sizes correspond to a small
child (age 5-6 years), medium child (age 10-12 years), teenaged child /small adult,
medium adult and large adult. The CTDI values in mGy/100 mAs per slice are measured
and compared with the values obtained using standard acrylic CTDI phantoms.
Measurements were made at different kVp values on different types of scanners (single
slice, two-slice, and four-slice) and different manufacturer’s CT scanners. Tables are
presented with conversion factors that allow one to convert conventional CTDI
measurements made with the standard acrylic phantom to CTDI values for different-sized
patients. For example, for one multi-slice scanner, the CTDIw value in mGy/100 mAs for
the small child phantom is twice the CTDIw measured in the acrylic abdominal phantom,
after converting air kerma to dose for the two phantom materials.