TH-EF-BRB-03: Enhancement of Image Contrast Along the Beam's-Eye-View (BEV) Direction Through Development of Imagers Based On Segmented Scintillators and Photon-Counting Arrays




The contrast provided by conventional portal imagers is constrained by inefficient conversion of the incident radiation, and by the small diagnostic x-ray component of the treatment beam. Toward improved visualization of the tumor region prior to treatment, as well as improved tumor tracking during treatment, progress is reported on the design of a pair of novel detectors that would address these constraints.


A dual-energy imager based on a segmented scintillator is being designed using a hybrid model to simulate radiation and optical transport. The simulations, which model operation with a megavoltage treatment beam and with a BEV imaging beam with a significant diagnostic component, employ parameters extracted from a previously developed prototype. Separately, the conceptual design of a second imager incorporating a 2D array of photon counting pixels is being explored through extrapolation of the design of the first prototype photon counting arrays fabricated using thin-film processing, a process scalable to very large area detectors.


The simulations identified a segmented scintillator imager design that, when operated with a BEV imaging beam, provides spatial resolution and contrast comparable to that of gantry-mounted kV imagers. When operated with a treatment beam, the design provides significantly improved DQE and contrast compared to conventional portal imagers. Extrapolation of initial photon counting array designs indicates that the circuitry necessary to provide energy-windowing of the diagnostic portion of a therapy beam can be achieved at the pixel pitch associated with current treatment room imagers.


These early studies demonstrate potential for improved contrast in projection and volumetric images obtained with the megavoltage beam prior to treatment, while also providing good performance when used with BEV imaging beams. In addition, these studies also support the possibility of improved capability for tumor tracking with such dual-energy imagers as well as by photon counting array imagers.

NIH grant R01-EB000558