Room: Exhibit Hall | Forum 2
Purpose: Range uncertainties can be significantly reduced with direct reconstruction of proton relative stopping power (RSP) via utilizing proton CT (p-CT). Pencil beam scanning (PBS) has been the treatment-modality-of-the-choice recently. In this simulation study, we investigate the efficacy and feasibility of using PBS for p-CT imaging.
Methods: A TOPAS Monte-Carlo model was developed based on PBS technology to simulate the p-CT acquisition/reconstruction. A 14cm-diameter cylinder water phantom was used in the simulation which was embedded with 3 groups of cylinders with different materials (ICRU bone, muscle, and adipose). Each group of cylinders contains three different sizes (2cm, 1cm, and 3mm in diameter). 180 projections were generated with 882 spots (200MeV, 500 protons/spot) on each 10x10cm projection (SAD=54.6cm and SDD=61.6cm). Spot spacing and size (1-sigma) were 5.4mm and around 6-8mm, respectively, on the detector. Statistical parameters were calculated on each spot based on spatial/energy histogram. Any proton with > 1std of mean residual energy and mean position were excluded. Detector noise was ignored and a direct path for proton transport route was assumed in a FDK-based reconstruction. P-CT imaging dose was calculated and accuracy of RSP reconstruction were analyzed in comparison to true values.
Results: Total dose to the phantom was 0.32mGy. The reconstructed RSP were 0.99Â±0.01(-1.0%) for the water, and 1.69Â±0.03(-1.7%), 1.03Â±0.01(0.0%), 0.97Â±0.01(-0.7%) for the 2cm, and 1.62Â±0.04(-5.8%), 1.02Â±0.01(-0.9%), and 0.97Â±0.02(-0.7%) for the 1cm bone, muscle and adipose cylinders, respectively. The 3mm bone cylinder was clearly visible, but not for the muscle and adipose, due to proton multi-coulomb scattering and straight path assumption for the reconstruction.
Conclusion: This is the first study to demonstrate the PBS proton beams being used directly for RSP reconstruction with great accuracy for ROIs >1cm. Further technology development is warranted and is in process to improve the resolution and the RSP accuracy for small ROIs.
Not Applicable / None Entered.