SU‐E‐T‐311: Comparison of Two Imaging Setups for Small Animal Cone Beam CT

Abstract

Purpose: To support non‐coplanar irradiation, cone beam CT (CBCT) on our small animal radiation research platform (SARRP) is acquired in a “pancake” setup where the prone animal is rotated between the stationary x‐ray source and flat‐panel detector. This study compares the performance of the pancake setup with conventional CBCT of a stationary animal. Methods: CBCT images were acquired on the SARRP using the pancake and a “tubular” setup with upright phantoms to mimic conventional CBCT. PMMA cylindrical phantoms of mouse dimension (3‐cm wide and 7.5‐cm long) embedded with 5‐mm wide rods of teflon, delrin, acrylic and polyethylene inhomogeneities were employed. The study included a single phantom, three side‐by‐side phantoms, and a euthanized mouse. Images were acquired at 65 kVp, 0.1‐mm brass filtration for: (1) imaging dose at 1x, 2x, and 4x of 1.6 cGy; (2) inclined “pancake” object at 14 degree and 28 degree. Comparison of zero‐frequency signal‐to‐noise ratio (SNR) and contrast‐to‐nose ratio (CNR) were made. Results: At 1.6 cGy, both SNR (19.4–23.0 vs 23.2–48.5) and CNR (−0.11%–0.57% vs −0.15%–0.88%) of the pancake setup were lower than those of the tubular setup for the 4 inhomogeneities. Similar results were obtained for the 3‐phantom study. Doubling the dose for the pancake setup improved these metrics and approached those of tubular setup at 1x dose. The difference in SNR and CNR between the pancake and tubular setups were reduced with increasing inclination. Pancake CBCT of an inclined mouse at 28 degree was virtually identical to that of the tubular setup. Conclusions: CBCT image quality of the pancake setup is compromised in favor of the ease of non‐coplanar irradiation. Image quality can be recovered with a modest increase in imaging dose to 3 cGy. Notwithstanding, pancake CBCT is adequate to support image guidance, while providing other irradiation advantages.John Wong has a sponsored research agreement with Xstrahl Ltd. Xstrahl Ltd. has a technology transfer agreement with Johns Hopkins University on the SARRP.