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On-Beam 4D CT Reconstruction Using Motion Amplitude Change Provided in Projection Images and Planning 4D CT

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J Jung

J Jung1*, S Park1 , J Kim2 , I Yeo3 , B Yi4 , (1) East Carolina University, Greenville, NC, (2) Stony Brook University Hospital, Stony Brook, NY, (3) Loma Linda Univ Medical Center, Loma Linda, CA, (4) Univ. of Maryland School Of Medicine, Baltimore, MD


SU-H2-GePD-J(B)-6 (Sunday, July 30, 2017) 3:30 PM - 4:00 PM Room: Joint Imaging-Therapy ePoster Lounge - B

Purpose: To reconstruct on-beam 4D CT images from planning 4D CT images by adapting deformation vector fields (DVFs) of the latter to the on-beam condition of patient.

Methods: A method was developed to reconstruct on-beam 4D CT images from planning 4D CT images using MV images acquired during therapeutic irradiations and those simulated thru planning 4D CT. To test this method, an anthropomorphic digital phantom (XCAT) with a spherical lung tumor object (3 cm in diameter) that moved by 1.25 cm and 2.09 cm was utilized, representing the time of planning CT acquisition and that of therapeutic irradiations, respectively. Actual patients’ respiratory traces were used to generate the phantom movement. Simulating therapeutic transit images, MV images were acquired by Monte Carlo modeling of EPID developed previously. In actual practices, the MV image set of therapeutic irradiations is obtained by transit beam measurement under patient. The tumor positions and their motion amplitudes were quantified for every phase. The DVFs in the planning 4D CT images were acquired for each phase from the base phase of EOE, and were multiplied by the amplitude ratio of the two image sets. The scaled DVFs were used to resample the planning 4D CT images generating on-beam 4D CT images. The generated images were compared with the reference on-beam images (2.09-cm motion).

Results: The 4D images showed good agreement within 1 mm residual errors with the reference images. The normalized cross correlation was greater than 99% for all image sets from EOE to EOI.

Conclusion: The method developed in this study was successfully validated. For the method to fully work, a base phase is required, that provides geometrically identical images between pretreatment and treatment conditions. The on-beam 4D images may be used for 4D dose reconstruction.

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