KaVo 3D eXam - Measurements

Kavo 3D eXam ® Operators’ Manual
K990400 16 April 2008
12-10
Where:
• Xr = the measured exposure in Roentgens
• f = a factor to convert exposure in air to absorbed dose in
tissue or other attenuating matter. One must use the f-factor
(f) appropriate to the task at hand to convert exposure (R) to
absorbed dose (rad):
i 0.78 rad/R for comparison to FDA-required,
manufacturer-reported data (Lucite), and this is also
appropriate for acrylic
i 0.93 or 0.98 rad/R for patient dose estimates (tissue or
water)
i 0.87 rad/R for calculation of, or comparison to, CTDIw
(air)
• 10 (cm) = the active length of the pencil-beam ion chamber
• NST = vertical dimension of the beam (6 cm)
9. Repeating these steps for different slice thicknesses is not
required as this is not applicable to the 17-19 Cone Beam
Volumetric Tomography technology.
10. Repeat for chamber in peripheral locations (1 cm interior to the
surface of the phantom) with all other holes filled with acrylic
rods.
Measurements
The following table consists of data gathered with the system 26.9s
scan, 120 kVp(eff), and 5mA. For completeness, the CTDI values
are calculated for all the three f factors given above.
radR Factor = 0.78 0.87 0.93
mrad mGy mrad
mGy mrad mGy
Center 238.2 2.38 265.7 2.66 284.0 2.84
Back Periphery 254.4 2.54 283.8 2.84 303.3 3.03
Left Periphery 220.2 2.20 245.6 2.46 262.5 2.63
Right Periphery 215.4 2.15 240.3 2.40 256.8 2.57
Front Periphery 172.2 1.72 192.1 1.92 205.3 2.05