Novel technology allowing cone beam CT in six seconds: a patient study of comparative image quality.

PURPOSE: The goal of this study was to evaluate the image quality provided by a novel cone beam CT (CBCT) platform (HyperSightTM , Varian Medical Systems), a platform with enhanced reconstruction algorithms as well as rapid acquisition times. Image quality was compared to both status quo CBCT for image guidance, and to fan beam CT (FBCT) acquired on a CT simulator (CTsim).

METHODS: In a clinical study, 30 subjects were recruited for whom either deep inspiration (DIBH) or deep exhalation breath hold (DEBH) was used during imaging and radiation treatment of tumors involving liver, lung, breast, abdomen, chest wall and pancreatic sites. All subjects were imaged during breath hold with CBCT on a standard image guidance platform (TrueBeam® 2.7, Varian Medical Systems) and FBCT CT (CTsim, GE Optima). HyperSight imaging with both breath hold (HSBH) and free breathing (HSFB) was performed in a single session. The four image sets thus acquired were registered and compared using metrics quantifying artifact index (AI), image non-uniformity, contrast, contrast-to-noise ratio (CNR), and difference of HU from CTsim.

RESULTS: HSBH provided less severe artifacts compared to both HSFB and TrueBeam. The severity of artifacts in HSBH images was similar to that in CTsim images, with statistically similar AI values. CTsim provided the best image uniformity, however HSBH provided improved uniformity compared to both HSFB and TrueBeam. CTsim demonstrated elevated contrast compared to HyperSight imaging, but both HSBH and HSFB imaging showed superior CNR characteristics compared to TrueBeam. The median HU difference of HSBH from CTsim was within 1 HU for muscle/fat tissue, 12 HU for bone and 14 HU for lung.

CONCLUSION: The HyperSight system provides six-second CBCT acquisition with image artifacts that are significantly reduced compared to TrueBeam and comparable to those in CTsim FBCT imaging. HyperSight breath hold imaging was of higher quality compared to free breathing imaging on the same system. The median HU value in HyperSight breath hold imaging is within 15 HU of that in CT simulation imaging for muscle, fat, bone and lung tissue types, indicating the utility of image data for direct dose calculation in adaptive workflows.