Po-Thur Eve General-18: Comparison of Imaging Performance: Cone Beam CT versus Conventional CT Simulators

Abstract

Cone Beam Computed Tomography(CBCT) is emerging as an alternative modality for radiotherapy treatment simulation and verification. Evaluation of CBCT performance for radiotherapy applications has been confined to in‐house built or modified CBCT devices. In this work, we investigated the imaging performance of a commercial (Varian Acuity) simulator having CBCT capability. The objective of this study was to compare its performance to that of a conventional CT simulator (Picker PQ5000) used for acquiring 3D data for generating radiotherapy treatment plans. Specifically the tests conducted include: density resolution, temporal stability, scan uniformity and spatial linearity, effect of varying scan widths, resolution (high and low contrast), and noise measurements, performed with a Catphan phantom. The variation in density resolution that is representative of the linearity in CT numbers was negligible for both modalities except for high density materials. Operational stability monitored by routinely tracking the CT numbers showed variations <14%, which we predict based on other studies, will result in only <2% uncertainty in dose calculations. Spatial resolution measurements showed better resolution capability for CBCT unlike for low contrast resolution, which was better for conventional CT. These results indicate that CBCT is comparable to CT and demonstrates its potential for treatment planning applications. We will explore this possibility further in future work. Currently, neither AAPM nor CAPCA, have standards for evaluating CBCT performance tolerances. Hence, we also anticipate that this study will provide guidelines for these documents when establishing tolerances for using commercial CBCT simulators.