Latest pCT Results from ProtonVDA

Speaker: Ethan DeJongh
Institution: ProtonVDA Inc, United States of America

Abstract

Purpose: Our research collaboration has developed a fully functional prototype proton imaging system that is designed to be simple, cost-effective, and suitable for practical use in clinical workflow. Using a low-intensity scanning pencil beam at the Northwestern Medicine Chicago Proton Center, we have acquired many experimental images for both radiography and pCT using meat samples as well as phantoms with known RSP. Our latest results include our first pCT scan in a gantry system and the development of a method to perform 3-D patient alignment using a single pRad. We have also developed a new iterative algorithm for pCT reconstruction which includes an objective stopping criterion for assurance of image quality.

Methods: Our system consists of tracking planes before and after the patient to track the positions of individual protons and a range detector to measure residual range. We employ Most Likely Path algorithms to determine proton paths through the patient and reconstruct images using a least-squares iterative algorithm. Our data acquisition system and reconstruction computer automatically process the data and produce an image within minutes. We use TOPAS to generate simulated proton images from X-Ray CT data for comparison with our experimental images. We create WEPL difference maps between the X-Ray and proton images to analyze range and alignment accuracy.

Results: pRad and pCT images of phantoms show good WEPL/RSP accuracy with errors below 1%. Comparisons of pCT and X-Ray CT images of the meat phantoms show significant RSP differences in bony and heterogeneous regions. A single pRad can correct for misalignments within 1 mm translation or 1 degree rotation in all directions.

Conclusion: With our prototype system, we have demonstrated the capability to produce proton images of sufficient quality for a variety of clinical uses and settings.

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