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Feasibility Study of 4D Image Reconstruction by Organ Motion Vector Extension Based On Portal Images

J Yoon

J Yoon1*, J Jung1 , I Yeo2 , J Kim3 , B Yi4 , (1) East Carolina University, Greenville, NC, (2) Loma Linda Univ Medical Center, Loma Linda, CA, (3) University of Pittsburgh Medical Center, Pittsburgh, PA, (4) Univ. of Maryland School Of Medicine, Baltimore, MD


SU-E-T-428 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:To develop and to test a method to generate a new 4D CT images of the treatment day from the old 4D CT and the portal images of the day when the motion extent exceeded from that represented by plan CTs.

Methods:A motion vector of a moving tumor in a patient may be extended to reconstruct the tumor position when the motion extent exceeded from that represented by plan CTs. To test this, 1. a phantom that consists of a polystyrene cylinder (tumor) embedded in cork (lung) was placed on a moving platform with 4 sec/cycle and amplitudes of 1 cm and 2 cm, and was 4D-scanned. 2. A 6MV photon beam was irradiated on the moving phantoms and cineEPID images were obtained. 3. A motion vector of the tumor was acquired from 4D CT images of the phantom with 1 cm amplitude. 4. From cine EPID images of the phantom with the 2 cm amplitude, various motion extents (0.3 cm, 0.5 cm, etc) were acquired and programmed into the motion vector, producing CT images at each position. 5. The reconstructed CT images were then compared with pre-acquired “reference” 4D CT images at each position (i.e. phase).

Results:The CT image was reconstructed and compared with the reference image, showing a slight mismatch in the transition direction limited by voxel size (slice thickness) in CT image. Due to the rigid nature of the phantom studied, the modeling the displacement of the center of object was sufficient. When deformable tumors are to be modeled, more complex scheme is necessary, which utilize cine EPID and 4D CT images.

Conclusion:The new idea of CT image reconstruction was demonstrated. Deformable tumor movements need to be considered in the future.

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