The necessity of inclusion of a virtual treatment couch involved in the XiO treatment planning system

Abstract

Objective To investigate the dosimetric effect of carbon fiber couch through virtual simulation in the XiO treatment planning system (TPS). Methods A treatment couch model of iBEAM evo Extension 650 was scanned with a big bore spiral CT and its contour was stored in the XiO TPS. The attenuation coefficient of couch was obtained by measuring the attenuated dose with and without a solid water phantom on the couch at different gantry angles (100°-180°). The optimal relative electron density (RED) values of the carbon fiber (CF) cover and foam core (FC) were adjusted according to the comparison between measured and simulated attenuation dose. The effects of the couch in the TPS on pass rate were evaluated by Octavius 4D phantom with 10 cases with lung cancer. Results The optimal RED values of CF and FC were 0.75 and 0.10 g/cm3, respectively. The measured attenuation error was the maximal at gantry angle of 120° (4.84%) without the treatment couch in the TPS. The average measured attenuation errors without the couch in the TPS dropped significantly from (2.54±1.48)% to (-0.04±0.36)% after inclusion of the treatment couch during dose calculation (Z=-3.621, P<0.05). The three-dimensional dose verification γ pass rate (3 mm/3%) without the couch increased significantly from (91.79±1.25)% to (94.74±1.69)% after inclusion of the couch in the dose calculation (t=6.027, P<0.05). Conclusions The effect of couch on the attenuation dose is significant. Inclusion of a virtual model of couch in XiO TPS can simulate the attenuation effect properly and improve the accuracy of dose calculation. Key words: Virtual treatment couch; XiO treatment planning system; Relative electron density; Octavius 4D phantom