A parallel, pipeline-based online analysis system for Interaction Vertex Imaging

TL;DR

This paper presents a parallel, pipeline-based system for real-time interaction vertex imaging in carbon ion radiotherapy, enabling online range monitoring within 200 ms to improve treatment safety.

Contribution

It introduces the first IVI system capable of achieving clinically-relevant online analysis times through optimized parallel processing and pipeline design.

Findings

Analysis delay is consistently under 200 ms.

Most computation time is spent on cluster formation.

System enables real-time range error detection during treatment.

Abstract

Objective Interaction vertex imaging (IVI) is used for range monitoring in carbon ion radiotherapy, detecting depth differences between Bragg peak positions. Online range monitoring, which provides feedback during beam delivery, is particularly desirable, creating an opportunity to detect range errors before the treatment fraction is completed. Incorporating online range monitoring into clinical workflows may therefore improve the safety and consistency of radiotherapy. Approach The data analysis system was broken into a task-parallel pipeline approach, to allow multiple analysis stages to occur concurrently, beginning during acquisition. Computationally-expensive operations were further parallelized to reduce bottleneck effects. Data collected from irradiation of homogeneous plastic phantoms was replayed at the same rate it was initially acquired, to mimic data acquisition, and the time required to determine a range shift was measured. Main Results With an optimized pipeline, the delay between the end of irradiation and the determination of a range shift is consistently less than 200 ms. The majority of this time is associated with the final range shift determination, with a minor effect from the time required to analyze the last data packet. The most significant contribution to an optimized analysis workflow is the formation of clusters, requiring almost 50% of compute time. Significance This system is the first IVI implementation to achieve clinically-relevant online analysis times. The 200 ms time required to determine a range shift is less than the time required to accelerate a new spill in a synchrotron, and is comparable to the time required for reacceleration if multiple energies are delivered in the same spill. Clinical implementation of online range monitoring would allow treatment to be quickly paused or aborted if significant range errors are detected.