Real-time single frame tomosynthesis: Prototype and radiotherapy applications

In conventional tomosynthesis, the x-ray source or detector move relative to the patient so that anatomy at a target depth is focused and other anatomy is blurred. We propose a real-time single frame tomosynthesis design using a distributed source array and a large flat-panel detector. Each element in the source array energizes simultaneously, and the beam is collimated down so that it passes through isocenter and is received in a small sector of the detector. The detector receives multiple non-overlapping x-ray images simultaneously, and averages these to blur anatomy outside the target depth. Reconstruction occurs at the readout rate of the detector, typically 30 frames per second. Single frame tomosynthesis therefore increases temporal resolution at the expense of field of view and number of views. An application of single frame tomosynthesis is the monitoring of lung tumors during stereotactic body radiotherapy (SBRT). External biplane fluoroscopic systems, presently used for management of cranial lesions, could be repurposed with tomosynthesis at moderate cost. In a reader study with two radiation oncologists evaluating 60 simulated cases of lung SBRT, 90% were deemed acceptable for motion management with tomosynthesis compared to 53% with fluoroscopy. We constructed a prototype system using four portable x-ray sources and a fixed collimator and frame and imaged an anthropomorphic lung phantom with a spherical lung nodule embedded, and found that the prototype system showed displayed the lung nodule with better contrast than fluoroscopy.