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A Fast, Accurate Simulation Strategy for MV-CBCT Image Generation

M Shi1,2*, M Myronakis2 , M Jacobson2 , M Lehmann3 , P Huber3 , R Fueglistaller3 , P Baturin4 , D Morf3 , D Ferguson2 , T Harris2 , I Valencia Lozano2 , C Williams2 , Y Hu2 , A Wang4 , R Berbeco2 , (1) University of Massachusetts Lowell, Lowell, MA, (2) Brigham and Women's Hospital, Dana-Farber Cancer Institute, and Harvard Medical School, Boston, MA, (3) Varian Medical Systems, Baden-Dattwil, Switzerland, (4) Varian Medical Systems, Palo Alto, CA


(Sunday, 7/14/2019) 3:30 PM - 4:00 PM

Room: Exhibit Hall | Forum 9

Purpose: Monte Carlo (MC) simulations of electronic portal imaging devices (EPID) requires intensive computation time, limiting development for applications as cone-beam computed tomography (CBCT). We have developed a novel technique, FastEPID, to significantly accelerate MC image simulation. The FastEPID method based on pre-calculated photon energy deposition efficiency (η) and optical photon spread functions (OSFs), has been introduced for fast simulation of MVCBCT.

Methods: OSFs and η are pre-calculated utilizing a validated EPID model. During FastEPID simulation, a mock detector (air volume) replaced the EPID model in the MC code. For each x-ray photon incident on the mock detector, the corresponding η and OSF were assigned according to its energy. If a newly generated random number (RN) was smaller than or equal to η, the incident photon was “detected�, otherwise it was discarded. For each detected photon, the corresponding OSF was added to final image with the center aligned to the incident position. 720 projections of an electron density phantom with a total dose of 12 MU were simulated with FastEPID and measurements were acquired on a clinical linear accelerator. Hounsfield units (HU) accuracy of the reconstructed MV CBCT images were compared between measurement and simulation. Improvement of simulation time utilizing the FastEPID method was quantified by the time ratio of conventional simulation and FastEPID simulation.

Results: The FastEPID simulation provided similar MV-CBCT image quality compared with measurement. Excellent agreement in HU accuracy was observed in multiple ROIs of the phantom. The FastEPID method has shortened MVCBCT simulation time by a factor of 43 compared to conventional simulation. Simulation of MV-CBCT images can now be performed in a matter of hours, rather than weeks.

Conclusion: The FastEPID method has significantly shorten simulation time without compromising image quality. Multiple applications, such as imager design optimization will benefit from this novel simulation method.

Funding Support, Disclosures, and Conflict of Interest: NIH/NCI R01CA188446


Monte Carlo, Megavoltage Imaging, Cone-beam CT


IM/TH- RT X-ray Imaging: CBCT imaging/therapy implementation

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