SU-E-J-167: Optimal Number of Respiratory Phases in 4D PET for Radiotherapy Planning: Motion-Simulated Phantom Study

Area of Science:

• Medical Imaging
• Radiotherapy Physics
• Nuclear Medicine

Background:

• Four-dimensional PET/CT (4D PET/CT) is crucial for accurate radiotherapy treatment planning.
• Determining the optimal number of respiratory phases (bins) for 4D PET/CT reconstruction remains an active area of research.
• Respiratory motion significantly impacts target delineation and dose delivery accuracy.

Purpose of the Study:

• To compare the effectiveness of 6-bin versus 10-bin reconstruction for 4D PET/CT in managing respiratory motion.
• To evaluate the impact of different numbers of respiratory bins on target volume delineation accuracy.
• To identify optimal parameters for 4D PET/CT reconstruction in radiotherapy planning.

Main Methods:

• A Jaszczak phantom with moving spheres simulating respiratory motion was used.
• Data were acquired using 18F-FDG with varying signal-to-background ratios (SBR) and motion amplitudes.
• Images were reconstructed using OSEM with optimized parameters and analyzed for volume distortions.

Main Results:

• Optimal static PET delineation parameters were identified as OSEM (32 subsets, 2 iterations), 5 mm FWHM, and 256x256 image size.
• 4D PET/CT studies revealed that a 6-bin reconstruction resulted in fewer volume distortions compared to a 10-bin reconstruction.
• Pre-calculated optimal thresholds derived from static data were applied to 4D data.

Conclusions:

• A 6-bin reconstruction strategy is more reliable for delineating moving targets in 4D PET/CT than a 10-bin strategy.
• Further research is needed to determine optimal thresholds derived from 4D data, rather than static data.
• This finding has implications for improving the accuracy of radiotherapy planning and delivery.