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A dose comparison study between XVI ® and OBI ® CBCT systems
Author(s) -
Song William Y.,
Kamath Srijit,
Ozawa Shuichi,
Al Ani Shlomi,
Chvetsov Alexei,
Bhandare Niranjan,
Palta Jatinder R.,
Liu Chihray,
Li Jonathan G.
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2825619
Subject(s) - imaging phantom , nuclear medicine , ionization chamber , monitor unit , linear particle accelerator , physics , cone beam computed tomography , materials science , beam (structure) , optics , medicine , computed tomography , radiology , ionization , ion , quantum mechanics
The purpose of this study is to establish a comprehensive set of dose measurements data obtained from the X‐ray Volumetric Imager (XVI ® , Elekta Oncology Systems) and the On‐Board Imager (OBI ® , 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 × 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 withR 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.