A CT Simulator Phantom for Geometrical Test

Min, Chul Kee; Yi, Byong Yong; Ahn, Seung Do; Choi, Eun Kyung; Chang, Hyesook

Abstract

PURPOSE
To design and test the CT simulator phantom for geometrical test. MATERIAL AND METHODS: The PMMA phantom was designed as a cylinder which is 20 cm in diameter and 24 cm in length, along with a 25x25x31 cm3 rectangular parallelepiped. Radio-opaque wires of which diameter is 0.8 mm are attached on the other surface of the phantom as a spiral. The rectangular phantom was made of four 24x24x0.5 cm3 square plates and each plate had a 24x24 cm2, 12x12 cm2, 6x6 cm2 square line. The squares were placed to face the cylinder at angles 0degrees, 15degrees, 30degrees, respectively. The rectangular phantom made it possible to measure the field size, couch angle, the collimator angle, the isocenter shift and the SSD, the measurements of the gantry angle from the cylindrical part. A virtual simulation software, AcQSimTM, offered various conditions to perform virtual simulations and these results were used to perform the geometrical quality assurance of CT simulator.
RESULTS
A 0.3~0.5 mm difference was found on the 24 cm field size which was created with the DRR measurements obtained by scanning of the rectangular phantom. The isocenter shift, the collimator rotation, the couch rotation, and the gantry rotation test showed 0.5~1 mm, 0.5~1degrees0.5~1degrees, and 0.5~ 1degreesdifferences, respectively. We could not find any significant differences between the results from the two scanning methods.
CONCLUSION
The geometrical test phantom developed in the study showed less than 1 mm (or 1degrees) differences. The phantom could be used as a routine geometrical QC/QA tools, since the differences are within clinically acceptable ranges.