Ng, Lydia W.

AbstractPurposeMobile lung tumors are increasingly being treated with ablative radiotherapy, for which precise motion management is essential. In‐room stereoscopic radiography systems are able to guide ablative radiotherapy for stationary cranial lesions but not optimally for lung tumors unless fiducial markers are inserted. We propose augmenting stereoscopic radiographic systems with multiple small x‐ray sources to provide the capability of imaging with stereoscopic, single frame tomosynthesis.MethodsIn single frame tomosynthesis, nine x‐ray sources are placed in a 3 × 3 configuration and energized simultaneously. The beams from these sources are collimated so that they converge on the tumor and then diverge to illuminate nine non‐overlapping sectors on the detector. These nine sector images are averaged together and filtered to create the tomosynthesis effect. Single frame tomosynthesis is intended to be an alternative imaging mode for existing stereoscopic systems with a field of view that is three times smaller and a temporal resolution equal to the frame rate of the detector. We simulated stereoscopic tomosynthesis and radiography using Monte Carlo techniques on 60 patients with early‐stage lung cancer from the NSCLC‐Radiomics dataset. Two board‐certified radiation oncologists reviewed these simulated images and rated them on a 4‐point scale (1: tumor not visible; 2: tumor visible but inadequate for motion management; 3: tumor visible and adequate for motion management; 4: tumor visibility excellent). Each tumor was independently presented four times (two viewing angles from radiography and two viewing angles from tomosynthesis) in a blinded fashion over two reading sessions.ResultsThe fraction of tumors that were rated as adequate or excellent for motion management (scores 3 or 4) from at least one viewing angle was 53% using radiography and 90% using tomosynthesis. From both viewing angles, the corresponding fractions were 7% for radiography and 48% for tomosynthesis. Readers agreed exactly on 62% of images and within 1 point on 98% of images. The acquisition technique was estimated to be 75 mAs at 120 kVp per treatment fraction assuming one verification image per breath, approximately one order of magnitude less than a standard dose cone beam CT.Conclusions Stereoscopic tomosynthesis may provide a noninvasive, low dose, intrafraction motion verification technique for lung tumors treated by ablative radiotherapy. The system architecture is compatible with real‐time video capture at 30 frames per second. Simulations suggest that most, but not all, lung tumors can be adequately visualized from at least one viewing angle.

PurposeFluoroscopy has been a tool of choice for monitoring treatments or interventions because of its extremely fast imaging times. However, the contrast obtained in fluoroscopy may be insufficient for certain clinical applications. In stereotactic ablative radiation therapy of the lung, fluoroscopy often lacks sufficient contrast for gating treatment. The purpose of this work is to describe and assess a real‐time tomosynthesis design that can produce sufficient contrast for guidance of lung tumor treatment within a small field of view.MethodsPrevious tomosynthesis designs in radiation oncology have temporal resolution on the order of seconds. The proposed system design uses parallel acquisition of multiple frames by simultaneously illuminating the field of view with multiple sources, enabling a temporal resolution of up to 30 frames per second. For a small field of view, a single flat‐panel detector could be used if different sectors of the detector are assigned to specific sources. Simulated images were generated by forward projection of existing clinical datasets. The authors varied the number of tubes and the power of each tube in order to determine the impact on tumor visualization.ResultsVisualization of the tumor was much clearer in tomosynthesis than in fluoroscopy. Contrast generally improved with the number of sources used, and a minimum of four sources should be used. The high contrast of the lung allows very low system power, and in most cases, less than 1 mA was needed. More power is required in the lateral direction than the AP direction.ConclusionsThe proposed system produces images adequate for real‐time guidance of radiation therapy. The additional hardware requirements are modest, and the system is capable of imaging at high frame rates and low dose. Further development, including a prototype system and a dosimetry study, is needed to further evaluate the feasibility of this device for radiation therapy guidance.