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. 2021 Aug 24;66(17):10.1088/1361-6560/ac1834.
doi: 10.1088/1361-6560/ac1834.

Proof-of-concept for x-ray based real-time image guidance during cardiac radioablation

Nicholas Hindley  1 , Suzanne Lydiard  1   2 , Chun-Chien Shieh  1   3 , Paul Keall  1
Affiliations

Proof-of-concept for x-ray based real-time image guidance during cardiac radioablation

Nicholas Hindley et al. Phys Med Biol. .

Abstract

Cardiac radioablation offers non-invasive treatments for refractory arrhythmias. However, treatment delivery for this technique remains challenging. In this paper, we introduce the first method for real-time image guidance during cardiac radioablation for refractory atrial fibrillation on a standard linear accelerator. Our proposed method utilizes direct diaphragm tracking on intrafraction images to estimate the respiratory component of cardiac substructure motion. We compare this method to treatment scenarios without real-time image guidance using the 4D-XCAT digital phantom. Pre-treatment and intrafraction imaging was simulated for 8 phantoms with unique anatomies programmed using cardiorespiratory motion from healthy volunteers. As every voxel in the 4D-XCAT phantom is labelled precisely according to the corresponding anatomical structure, this provided ground-truth for quantitative evaluation. Tracking performance was compared to the ground-truth for simulations with and without real-time image guidance using the left atrium as an exemplar target. Differences in target volume size, mean volumetric coverage, minimum volumetric coverage and geometric error were recorded for each simulation. We observed that differences in target volume size were statistically significant (p < 0.001) across treatment scenarios and that real-time image guidance enabled reductions in target volume size ranging from 11% to 24%. Differences in mean and minimum volumetric coverage were statistically insignificant (bothp = 0.35) while differences in geometric error were statistically significant (p = 0.039). The results of this study provide proof-of-concept for x-ray based real-time image guidance during cardiac radioablation.

Keywords: cardiac; guidance; radioablation; real-time.

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Conflict of interest statement

Conflicts of interest

The University of Sydney filed a provisional patent for the method detailed in this paper. The authors are inventors on this patent.

Figures

Figure 1.
Figure 1.
A pictographic representation of the proposed clinical workflow, consisting of three pre-treatment steps and two steps during treatment. Pre-treatment; first, the intracardiac target, heart and diaphragm are segmented; second, peak-inhale to peak-exhale registration is used to estimate the trajectories of target and diaphragm motion; and third, the relative contribution of diaphragm to target motion computed to generate a patient-specific respiratory motion model. During treatment; first, the diaphragm is tracked on each kV projection using an in-house algorithm; and second, diaphragm tracking is combined with the patient-specific respiratory motion model to estimate the intracardiac target position.
Figure 2.
Figure 2.
A pictographic representation of the validation workflow, in which target volumes for scenarios with and without real-time image guidance (PTVC and PTVR+C respectively) are compared to the corresponding ground-truth using target volume size, volumetric coverage and geometric error.
Figure 3.
Figure 3.
Tracking performance for the first minute of the simulation with the lowest 3D error (Phantom 2), including example projections at lateral and ventral views overlaid with ground-truth target, shifted PTVC, unshifted PTVR+C, heart and diaphragm positions in green, solid red, magenta, dashed red and blue respectively (above) as well as motion traces for the ground-truth target, shifted PTVC and unshifted PTVR+C centroid positions in green, red and magenta respectively (below).
Figure 4.
Figure 4.
Tracking performance for the first minute of the simulation with the highest 3D error (Phantom 7), including example projections at lateral and ventral views overlaid with ground-truth target, shifted PTVC, unshifted PTVR+C, heart and diaphragm positions in green, solid red, magenta, dashed red and blue respectively (above) as well as motion traces for the ground-truth target, shifted PTVC and unshifted PTVR+C centroid positions in green, red and magenta respectively (below).
Figure 5.
Figure 5.
Tracking performance for the first minute of the simulation with the lowest target coverage (Phantom 1), including example projections at lateral and ventral views overlaid with ground-truth target, shifted PTVC, unshifted PTVR+C, heart and diaphragm positions in green, solid red, magenta, dashed red and blue respectively (above) as well as motion traces for the ground-truth target, shifted PTVC and unshifted PTVR+C centroid positions in green, red and magenta respectively (below).
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