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Optimal Number of Respiratory Phases in 4D PET for Radiotherapy Planning: Motion-Simulated Phantom Study

M Budzevich

M Budzevich*, T Dilling, G Zhang, C Kuykendall, E Moros, H. Lee Moffitt Cancer Center, TAMPA, FL

SU-E-J-167 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: Four-dimensional PET/CT is increasingly used in radiotherapy treatment planning. One issue that is still under investigation is the optimal number of bins or phases into which the respiratory cycle needs to be divided. We performed 4D PET moving phantom study and compared results between 6 and 10 bins.

Methods: A Jaszczak Phantom™ containing six hollow spheres (0.95 - 3.18 cm inner diameters) was used. Three sinusoidal motion patterns were accomplished with peak-to-peak amplitudes of 1, 1.5 and 2.0 cm with a respiratory period of 5 s. The background and the six spheres were filled with 18F-FDG solution to achieve three SBR: 1:3.65, 1:7.95, and 1:10.22. Data were collected in 3-D mode for 10 min. Images were reconstructed using OSEM reconstruction: 32 subsets with 2 iterations, variable FWHM Gaussian post-filter 5-8 mm, and using image matrix sizes of 128x128, 192x192 and 256x256. The spheres were auto-segmented using pre-calculated optimal thresholds for a 1:1 volumetric correlation between actual- and PET-delineated spheres from static phantom studies.

Results: According to the static data the following set of parameters are optimal for static PET target (sphere) delineation: OSEM reconstruction with 32 subsets and 2 iterations, FWHM of 5 mm, and image size 256x256. The 4D data studies (with pre-calculated optimal thresholds) have shown that a 6-bin set shows less volume distortions then the 10-bin set.

Conclusions: The authors found that 6-bin reconstruction is more reliable for delineation of a target in motion than 10-bin reconstruction. Further investigation with optimal thresholds obtained from 4D data, not static, is required.

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