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Research Papers

A New Catheter for Tumor-Targeting With Radioactive Microspheres in Representative Hepatic Artery Systems—Part II: Solid Tumor-Targeting in a Patient-Inspired Hepatic Artery System

[+] Author and Article Information
E. M. Childress

Department of Mechanical and Aerospace Engineering,  North Carolina State University, Raleigh, NC 27695

C. Kleinstreuer1 n2

Department of Mechanical and Aerospace Engineering, Joint Department of Biomedical Engineering,  North Carolina State University, Raleigh, NC 27695;  University of North Carolina at Chapel Hill, Chapel Hill, NC 27599ck@eos.ncsu.edu

A. S. Kennedy

Radiation Oncology,  Cancer Centers of North Carolina, Cary, NC 27518

1

Corresponding author.

2

Site where research was performed.

J Biomech Eng 134(5), 051005 (May 25, 2012) (10 pages) doi:10.1115/1.4006685 History: Received October 20, 2011; Revised April 11, 2012; Online May 25, 2012; Posted May 30, 2012; Published June 05, 2012

In this second part, the methodology for optimal tumor-targeting is further explored, employing a patient-inspired hepatic artery system which differs significantly from the idealized configuration discussed in Part I. Furthermore, the fluid dynamics of a microsphere supply apparatus is also analyzed. The best radial catheter positions and particle-release intervals for tumor targeting were determined for both the idealized and patient-inspired configurations. This was accomplished by numerically analyzing generated particle release maps (PRMs) for ten equally spaced intervals throughout the pulse. As in Part I, the effects of introducing a catheter were also investigated. In addition to the determination of micro-catheter positioning and, hence, optimal microsphere release, a microsphere-supply apparatus (MSA) was analyzed, which transports the particles to the catheter-nozzle, considering different axial particle injection functions, i.e., step, ramp, and S-curve. A refined targeting methodology was developed which demonstrates how the optimal injection region and interval can be determined with the presence of a catheter for any geometric configuration. Additionally, the less abrupt injection functions (i.e., ramp and S-curve) were shown to provide a more compact particle stream, making them better choices for targeting. The results of this study aid in designing the smart micro-catheter (SMC) in conjunction with the MSA, bringing this innovative treatment procedure one step closer to implementation in clinical practice.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Basic, and (b) patient-inspired hepatic artery configurations with associated boundary waveforms. Online figures are in color.

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Figure 2

Eccentric annulus geometry (adapted from Snyder and Goldstein [7]). The inner boundary represents the outer wall of the catheter while the outer boundary represents the inner wall of the vessel. Here, rcath,out  = outer radius of catheter, rvess  = inner radius of vessel, ecc = eccentricity of annulus, or the distance between the vessel and catheter centers, and xcath and xvess  = the x-position of the catheter and vessel, respectively, relative to the given coordinate system. Online figures are in color.

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Figure 3

Catheter injection velocity to vessel velocity ratio versus time for four microsphere-suspension input functions. Online figures are in color.

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Figure 4

(a) Variation of PRMs over pulse for the basic configuration, and (b) the CPRM (all intervals) without catheter. Included are the boundary conditions which reveal how the intervals were divided. Slight changes in the PRMs from intervals 1–10 and distinct regions in the CPRM suggest that targeting throughout the pulse may be achieved for certain branches. Online figures are in color.

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Figure 5

(a) Variation of PRMs over pulse for the patient-inspired configuration, and (b) the CPRM (all intervals) without catheter. Included are the boundary conditions which reveal how the intervals were divided. Regions in these PRMs are not as well defined and changed more drastically throughout the pulse compared to those of the basic configuration (see Fig. 4). The CPRM shows considerable overlapping of the regions, and, thus, no clear injection region is observed for individual branch targeting of either the LHA or RHA. It does, however, reveal that the SMA can be avoided by injecting near the center of the injection plane (i.e., the indicated region where only the blue and red regions overlap). Online figures are in color.

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Figure 6

Targeting D1 in the basic configuration: (a) the initial catheter position determined using the CPRM without the catheter presence, and (b) PRMs for the initial catheter position. The white crosshair illustrates whether targeting to D1 can be achieved from the catheter position, while the black crosshair denotes when targeting cannot be achieved. Included are the boundary conditions, which reveal how the intervals were divided. The overlapping regions in and near the crosshairs for all intervals but interval 3 suggests that targeting can only be achieved in interval 3 at this initial catheter position. Online figures are in color.

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Figure 7

Targeting D1 in the basic configuration: (a) the adjusted catheter position on the CPRM without the catheter, and (b) PRMs for the adjusted position. The boundary conditions are the same as in Fig. 6. Again, white crosshairs indicate targeted injection to D1, while black crosshairs indicate nontargeted injection. From this position, D1 targeting can be achieved in intervals 2–9. This is a major improvement over the initial position (see Fig. 6). Online figures are in color.

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Figure 8

Targeting RHA and LHA in the patient-inspired configuration: (a) the catheter position, and (b) PRMs. Included are the boundary conditions which reveal how the intervals were divided. The white crosshair illustrates whether targeting to the LHA and RHA can be achieved from the catheter position, while the black crosshair denotes when targeting cannot be achieved. From this catheter position, targeting can be achieved in intervals 6–9. Online figures are in color.

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Figure 9

(a) Velocity vectors at the symmetry plane 0.01 s after the start of the injection, and (b) particle trajectories at 1 s for four suspension-input functions (given in Fig. 3) in an ideal 6 mm diameter straight vessel with a centered 0.75 mm outer diameter catheter. Particle trajectories are colored according to the particle time (actual time). For the ramp and S-curve functions, particles are initially trapped in a recirculation region at the catheter tip, and only a narrow stream of particles exit this region until the injection velocity reaches the vessel velocity. For the step function, the particles initially expand out of the steady injection stream. Online figures are in color.

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Figure 10

Particle trajectories for microspheres caught in recirculation after shut-off. Included is the ramp up–step down input function that was employed. The particle trajectories are colored according to the particle time (actual time), which illustrates that the particles that were introduced near the end of the injection begin to recirculate near the tip of the catheter. Online figures are in color.

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Figure 11

(a) Minimum particle traveling time versus catheter length for two injection velocities, and (b) average flushing time versus particle injection duration for a 75 cm catheter and two injection velocities. Online figures are in color.

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