An eight-channel detector for an 192Ir brachytherapy source-based computed tomography scanner

Brachytherapy (BT) is a well-established treatment modality that requires accurate localization of holders with respect to the tumor and nearby critical structures. Computed tomography (CT) is ideal for imaging the source holders. In this paper, we describe a solid-state eight-channel detector designed for a fourth-generation CT scanner that uses a high-dose-rate BT source to provide the photons needed to form an image. The detector comprises eight 0.8×0.275×1.0 cm³ CdWO₄ scintillation crystals, a linear photodiode array, gated integrator, low-pass-filter gain stage, sample-and-hold, and multiplexer electronics. The detector response to light is linear for light intensities between 8×10^-11 W/cm² and 3×10^-8 W/cm². Using a 5.3 Ci ¹⁹² Ir source positioned 82.5 cm from the detector, the signal-to-noise ratio (SNR) with no attenuation in the path of the beam is 118; with 41 cm of Plexiglas placed between the source and the detector, the SNR is 12. In addition, the detector signal is much larger than the electronic noise floor for up to at least 43 cm of Plexiglas, demonstrating that this detector is suitable for use in an ¹⁹²Ir-based CT scanner. A preliminary image obtained using the detector in a first-generation geometry is presented