A Highly Accelerated Parallel Multi-GPU based Reconstruction Algorithm for Generating Accurate Relative Stopping Powers

Low-dose Proton Computed Tomography (pCT) is an evolving imaging modality that is used in proton therapy planning which addresses the range uncertainty problem. The goal of pCT is generating a 3D map of Relative Stopping Power (RSP) measurements with high accuracy within clinically required time frames. Generating accurate RSP values within the shortest amount of time is considered a key goal when developing a pCT software. The existing pCT softwares have successfully met this time frame and even succeeded this time goal, but requiring clusters with hundreds of processors. This paper describes a novel reconstruction technique using two Graphics Processing Unit (GPU) cores, such as is available on a single Nvidia P100. The proposed reconstruction technique is tested on both simulated and experimental datasets and on two different systems namely Nvidia K40 and P100 GPUs from IBM and Cray. The experimental results demonstrate that our proposed reconstruction method meets both the timing and accuracy with the benefit of having reasonable cost, and efficient use of power.Comment: IEEE NSS/MIC 201

Rebinning errors in coincidence imaging due to depth of interaction

In positron emission tomography, uncertainties in - or lack of knowledge of - depths of interaction lead to errors in the positioning of coincidence events. This paper examines the dependence of these positioning errors on depth of interaction. Here derived are analytic expressions that relate rebinning errors to the uncertainties in the measurement of interaction positions including depth of interaction. The results confirm the intuitive notion that rebinning errors are minimized when depth of interaction is measured at least as well as the transverse position

Comparison of wavelength-shifting fiber types and methods of ribbon assembly for the Depth-encoding Anger detector

We are developing a depth-encoding Anger detector for imaging 511 keV annihilation photons. Our design integrates wavelength-shifting (WLS) fibers onto an Anger-type detector to allow measurement of depth-of-interaction (DOI). As few as 0.3% of blue scintillation photons created in NaI(Tl) contribute to detectable signal at the end of the WLS fiber ribbon. Thus, maximizing signal output from the fibers is important for achieving the best possible DOI measurement. We have investigated the effects of two design options on the signal output from the WLS fibers: fiber geometry and methods of assembling fibers into a ribbon. A blue-to-green WLS fiber (Saint Gobain BCF-91A) was chosen because its absorption spectrum matches well the emission spectrum of NaI(Tl). Its emissions, peaked at 500 nm, can be detected with reasonable quantum efficiency by enhanced-green-response PMTs. These fibers are available in several configurations (round or square cross-section, single or multiple cladding layers) and sizes. Methods for assembling the fibers into a ribbon include the use of mechanical clamps and adhesives. Finally, reflectors can be used to increase the total light output from the ribbon. In this work we compare single-clad 1-mm-diameter round fibers to multi-clad 1-mm-wide square fibers. We also compare cellophane adhesive tape, acrylic-solvent-based cements, and mechanical clamping as possible methods for binding WLS fibers into a ribbon. Our results indicate that square cross-section fibers with multiple layers of cladding outperform single-clad round cross-section fibers. Additionally, aluminized reflectors on certain regions of the fiber ribbon are useful. Placing acrylic mounting components in direct contact with the fibers causes excessive light loss from the ribbon. Solvent-based adhesives, which partially dissolve the cladding material, decrease light output from the ribbon; cellophane adhesive tape or aluminized-face mechanical clamps perform well. In the future, we will extend our investigation to other fiber sizes and cladding configurations

Accuracy of low-dose proton CT image registration for pretreatment alignment verification in reference to planning proton CT

Purpose: Proton CT (pCT) has the ability to reduce inherent uncertainties in proton treatment by directly measuring the relative proton stopping power with respect to water, thereby avoiding the uncertain conversion of X-ray CT Hounsfield unit to relative stopping power and the deleterious effect of X- ray CT artifacts. The purpose of this work was to further evaluate the potential of pCT for pretreatment positioning using experimental pCT data of a head phantom. Methods: The performance of a 3D image registration algorithm was tested with pCT reconstructions of a pediatric head phantom. A planning pCT simulation scan of the phantom was obtained with 200 MeV protons and reconstructed with a 3D filtered back projection (FBP) algorithm followed by iterative reconstruction and a representative pretreatment pCT scan was reconstructed with FBP only to save reconstruction time. The pretreatment pCT scan was rigidly transformed by prescribing random errors with six degrees of freedom or deformed by the deformation field derived from a head and neck cancer patient to the pretreatment pCT reconstruction, respectively. After applying the rigid or deformable image registration algorithm to retrieve the original pCT image before transformation, the accuracy of the registration was assessed. To simulate very low-dose imaging for patient setup, the proton CT images were reconstructed with 100%, 50%, 25%, and 12.5% of the total number of histories of the original planning pCT simulation scan, respectively. Results: The residual errors in image registration were lower than 1 mm and 1° of magnitude regardless of the anatomic directions and imaging dose. The mean residual errors ranges found for rigid image registration were from −0.29 ± 0.09 to 0.51 ± 0.50 mm for translations and from −0.05 ± 0.13 to 0.08 ± 0.08 degrees for rotations. The percentages of sub-millimetric errors found, for deformable image registration, were between 63.5% and 100%. Conclusion: This experimental head phantom study demonstrated the potential of low-dose pCT imaging for 3D image registration. Further work is needed to confirm the value pCT for pretreatment image-guided proton therapy