B. Erdelyi

Distributed and hardware accelerated computing for clinical medical imaging using proton computed tomography (pCT)

Proton computed tomography (pCT) is an imaging modality that has been in development to support targeted dose delivery in proton therapy. It aims to accurately map the distribution of relative stopping power. Because protons traverse material media in non-linear paths, pCT requires individual proton processing. Image reconstruction then becomes a time-consuming process. Clinical-use scenarios that require images from billions of protons in less than ten or fifteen minutes have motivated us to use distributed and hardware-accelerated computing methods to achieve fast image reconstruction. Combined use of MPI and GPUs demonstrates that clinically viable image reconstruction is possible. On a 60-node CPU/GPU computer cluster, we achieved efficient strong and weak scaling when reconstructing images from two billion histories in under seven minutes. This represents a significant improvement over the previous state-of-the-art in pCT, which took almost seventy minutes to reconstruct an image from 131 million histories on a single-CPU, single-GPU computer.

A comprehensive study of the most likely path formalism for proton-computed tomography

We investigate some generalizations of the most likely path formalism developed for proton-computed tomography. The stochastic path of a proton inside a homogeneous medium is replaced by a deterministic smooth path that maximizes the probability of the proton passing through the points on this curve, given measured entrance and exit parameters for each individual proton. We study various factors that influence this curve and the associated error envelopes. These factors are the influence of the energy loss, a logarithmic correction factor in the small angle Coulomb scattering and the importance of path length versus material thickness. We develop a method for further constraining the possible proton paths by including energy information in the derivation of the most likely path, utilizing an infinite-dimensional constrained functional analysis method. It is shown that while there is an additional uncertainty on the most likely path that is difficult to determine experimentally, the associated error envelopes are smaller, resulting in possibly slightly improved spatial resolution for proton-computed tomography.

Detector development for Proton Computed Tomography (pCT)

Proton Computed Tomography (pCT) is being developed in support of proton therapy and treatment planning. The aim of pCT, to reconstruct an accurate map of the stopping power (S.P.) in a phantom and, in the future, in patients, is being pursued with a diverse list of detector systems, using the entire arsenal of tracking and energy detectors developed for High Energy Physics (HEP). The first radiographs and 3D images are being reconstructed with prototype detectors, which will be described. Most of the existing systems are being upgraded to higher proton fluxes to reduce the scanning time.

Development of Proton Computed Tomography for Applications in Proton Therapy

Determination of the Bragg peak position in proton therapy requires accurate knowledge of the electron density and ratio of effective atomic number and mass (Z/A) of the body tissues traversed. While the Z/A ratio is fairly constant for human tissues, the density of tissues varies significantly. One possibility to obtain accurate electron density information of tissues is to use protons of sufficient energy to penetrate the patient and measure their energy loss. From these transmission measurements, it is possible to reconstruct a three‐dimensional map of electron densities using algebraic techniques. The interest in proton computed tomography (pCT) has considerably increased in recent years due to the more common use of proton accelerators for cancer treatment world‐wide and a modern design concept based on current high‐energy physics technology has been suggested. This contribution gives a status update on the pCT project carried out by the pCT Collaboration, a group of institutions sharing interest and...

Parametric-resonance ionization cooling of muon beams

Parametric-resonance Ionization Cooling (PIC) is proposed as the final 6D cooling stage of a high-luminosity muon collider. Combining muon ionization cooling with parametric resonant dynamics should allow an order of magnitude smaller final equilibrium transverse beam emittances than conventional ionization cooling alone. In this scheme, a half-integer parametric resonance is induced in a cooling channel causing the beam to be naturally focused with the period of the channel’s free oscillations. Thin absorbers placed at the focal points then cool the beam’s angular divergence through the usual ionization cooling mechanism where each absorber is followed by RF cavities. A special continuous-field twin-helix magnetic channel with correlated behavior of the horizontal and vertical betatron motions and dispersion was developed for PIC. We present the results of modeling PIC in such a channel using GEANT4/G4beamline. We discuss the challenge of precise beam aberration control from one absorber to another over ...

Fringe field effects in muon rings

Because of the predominance of large emittances, muon storage rings have a tendency to being rather sensitive to nonlinear effects. In this paper we study the effects of the nonlinearities due to the lattice elements’ fringe fields, which have a fundamentally different behavior from normal multipole terms. It is found that for given scenarios for lattices and emittances, the fringe field effects have dramatic influences on the dynamics and stability of particles and hence require careful study of correction options.

DIFFERENTIAL ALGEBRAIC DETERMINATION OF HIGH-ORDER OFF-ENERGY CLOSED ORBITS, CHROMATICITIES, AND MOMENTUM COMPACTIONS

Abstract For some modern particle accelerators, including the planned muon collider, the accurate analysis of non-linear time-of-flight effects in the form of momentum compactions is critical for the preservation of bunch structure. A Differential Algebra-based (DA) method is presented that allows the determination of off-energy closed orbits and chromaticities to any order. By performing a coordinate transformation to the off-energy closed orbit, it is possible to compute momentum compactions analytically. This method has been implemented in the code COSY INFINITY and is tested for two cases where analytical solutions can be obtained by hand; agreement to machine precision is found. By contrast, comparisons are made with several codes that use conventional numerical methods for the determination of momentum compaction, and it is found that these approaches sometimes yield rather inaccurate results, especially for higher orders.

Development of a proton Computed Tomography Detector System

Computer tomography is one of the most promising new methods to image abnormal tissues inside the human body. Tomography is also used to position the patient accurately before radiation therapy. Hadron therapy for treating cancer has become one of the most advantegeous and safe options. In order to fully utilize the advantages of hadron therapy, there is a necessity of performing radiography with hadrons as well. In this paper we present the development of a proton computed tomography system. Our second-generation proton tomography system consists of two upstream and two downstream trackers made up of fibers as active material and a range detector consisting of plastic scintillators. We present details of the detector system, readout electronics, and data acquisition system as well as the commissioning of the entire system. We also present preliminary results from the test beam of the range detector.

ON SOME ERRORS AND BIAS IN PROTON COMPUTED TOMOGRAPHY

Novel accelerator technology, including Fixed Field Alternating Gradient Accelerators (FFAG) coupled with medical imaging devices, hold significant promise for enhanced proton therapy. The accuracy and efficiency of proton therapy treatments will see improvements with the implementation of proton computed tomography (pCT), currently under development. Here, we analyze the robustness of the image reconstruction method in pCT with respect to three different error sources and conclude that pCT is inherently resilient with respect to errors in mean ionization potential, discrete sampling of proton trajectories and bias in the limit of large radiation doses.

The Effect of Tissue Inhomogeneities on the Accuracy of Proton Path Reconstruction for Proton Computed Tomography

Maintaining a high degree of spatial resolution in proton computed tomography (pCT) is a challenge due to the statistical nature of the proton path through the object. Recent work has focused on the formulation of the most likely path (MLP) of protons through a homogeneous water object and the accuracy of this approach has been tested experimentally with a homogeneous PMMA phantom. Inhomogeneities inside the phantom, consisting of, for example, air and bone will lead to unavoidable inaccuracies of this approach. The purpose of this ongoing work is to characterize systematic errors that are introduced by regions of bone and air density and how this affects the accuracy of proton CT in surrounding voxels both in terms of spatial and density reconstruction accuracy. Phantoms containing tissue‐equivalent inhomogeneities have been designed and proton transport through them has been simulated with the GEANT 4.9.0 Monte Carlo tool kit. Various iterative reconstruction techniques, including the classical fully se...