WE-E-201B-05: Image Quality Improvement in Megavoltage Cone Beam CT Using an Ultrafast Ceramic Scintillator System

Abstract

Purpose: To quantitatively and qualitatively assess improvement in megavoltage cone beam CT (MVCBCT) image quality afforded by a 4.2 MV imaging beam line (IBL) with a carbon electron target and new pixelated ultrafast ceramic scintillator (UFC) detector, relative to the 6 MV treatment beam line (TBL). Detector blur is reduced with the UFC since light generated in a pixel is less likely to escape laterally. Methods: A prototype IBL+UFC system was installed on a Siemens ONCOR linear accelerator equipped with the MVision™ IGRT system. A UFC strip consisting of four tiles and measuring ∼40 cm by ∼10 cm was installed on the flat panel imager, with the long dimension in the cross‐plane direction. Phantom images were acquired at doses from 2–60 cGy with the TBL, IBL with conventional scintillator, and IBL+UFC. Several head and neck, thoracic, and pelvic patients were imaged with the three systems at doses from 2–15 cGy. Results: Phantom images indicate that the IBL+UFC images have lower noise and higher contrast than the IBL and TBL images. The contrast‐to‐noise ratio (CNR) for the IBL was 1.5–2 times higher than for the TBL, and the IBL+UFC CNR was 1.5–2 times better than for the IBL at all doses. CNR saturated near 30 cGy for the IBL+UFC and at 60 cGy or greater for the IBL and TBL. IBL+UFC patient images showed improved soft tissue contrast at all doses and sites examined. Conclusions: The IBL+UFC combination increases the CNR by up to a factor of four relative to the TBL with the conventional scintillator, and a factor of two relative to the IBL with the conventional scintillator. Imagenoise and soft tissue contrast in head and neck, thoracic, and pelvic patients improved dramatically in the IBL+UFC images relative to the TBL images. Sponsored partially by Siemens Oncology Care Systems.