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1766152 
Journal Article 
A dose comparison study between XVI (R) and OBI (R) CBCT systems 
Song, WY; Kamath, S; Ozawal, S; Al Ani, S; Chvetsov, A; Lhandare, N; Palta, JR; Liu, C; Li, JG 
2008 
1 
Medical Physics
ISSN: 0094-2405 
35 
2 
480-486 
18383668 
WOS:000253318400009 
The purpose of this study is to establish a comprehensive
set of dose measurements data obtained from the X-ray Volumetric Imager (XVI (R), Elekta Oncology
Systems) and the On-Board Imager (01310, Varian Medical Systems) cone-beam CT (CBCT) systems. To
this end, two uniform-density cylindrical acrylic phantoms with diameters of 18 cm (head phantom)
and 30 cm (body phantom) were used for all measurements. Both phantoms included ion chamber
placement holes in the center and at periphery (2 cm below surface). For the XVI unit, the four
standard manufacturer-supplied protocols were measured. For the OBI unit, the full bow tie and
half bow tie (and no bow tie) filters were used in combination with the two scanning modes;
namely, full-fan and half-fan. The total milliampere X seconds (mA s) setting was also varied for
each protocol to establish the linear relationship between the dose deposited and the mA s used
(with all other factors being held constant). Half-value layers in aluminum (Al) were also
measured for beam characteristic determination. For the XVI unit, the average dose ranged from
0.1 to 3.5 cGy with the highest dose measured using the ""prostate"" protocol with the body
phantom. For the OBI unit, the average dose ranged from 1.1 to 8.3 cGy with the highest dose
measured using the full-fan protocol with the head phantom. The measured doses were highly linear
as a function of mA s, for both units, where the measurement points followed a linear
relationship very closely with R-2 > 0.99 for all cases. Half-value layers were between 4.6- and
7.0-mm-Al for the two CBCT units where XVI generally had more penetrating beams at the similar
kVp settings. In conclusion, a comprehensive series of dose measurements were performed on the
XVI and the OBI CBCT units. In the process, many of the important similarities and differences
between the two systems were observed and summarized in this work. (C) 2008 American Association
of Physicists in Medicine. 
cone-beam CT; dose measurements; IGRT; XVI; OBI