A high quantum efficiency prototype video based portal imaging system

摘要

Current video-based electronic portal imaging devices (VEPIDs) that utilize thin phosphor screens have poor image quality due to low light collection. Expensive flat-panel imagers with the same screen yield higher quality imaging at 2-4 monitor-units (MU) exposures, but are susceptible to radiation damage to the peripheral electronics. A prototype thick scintillation crystal (TSC) VEPID for subMU exposures is presented here. Utilizing a 12 mm thick CsI(Tl) crystal scintillator for greater light production, the detective quantum efficiency (DQE) is significantly increased for the prototype TSC (17 × 17 cm~2 field-of-view at isocenter) while spatial resolution is not affected by the increased optical path. A high-resolution plumbicon camera with 12-bit ADC and computer-controlled target integration provides variable exposure imaging. Modulation transfer function (MTF) and DQE measurements along with phantom imaging are presented for the TSC, commercial VEPIDs, flat-panels and film. The DQE for TSC is significantly higher than current VEPIDs, and comparable to flat-panel at low frequency. TSC provides portal imaging superior to other VEPIDs at subMU exposures. The TSC provides high quality portal imaging and with further optimization is expected to be better or comparable to flat-panels. TSC subMU imaging has potential for intra-treatment patient position monitoring, and increased portal verification frequency for patient localization.