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Cardiac Substructure Tracking During Ablative Radiotherapy

N Hindley1*, C Shieh2, S Lydiard1,3,4, T Reynolds1, P Keall1 (1) ACRF Image X Institute, University of Sydney, NSW, Australia (2) Brain and Mind Research Institute, University of Sydney, NSW, Australia (3) Ingham Institute for Applied Medical Research, NSW, Australia (4) Department of Radiation Oncology, Auckland District Health Board, AU, New Zealand


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Stereotactic radioablation has shown recent promise in the treatment of cardiac arrhythmias. However, existing approaches typically expand target volumes to encompass both cardiac and respiratory motion. This unnecessarily endangers healthy tissue. We developed an algorithm which utilizes diaphragm tracking to account for the respiratory component of cardiac substructure motion. The algorithm was validated using the pulmonary vein antrum (PVA) as a prospective target on a digital phantom.

Method: Our proposed workflow consists of five steps: (1) The diaphragm and target are segmented on a 4D-CT (2) The trajectories of diaphragm and target motion are estimated by end-exhale to end-inhale registration (3) The relative contribution of diaphragm to target motion is computed (4) The diaphragm is tracked on each intrafraction kV projection (5) The respiratory component of 3D target motion is estimated. Each 4D-CT and kV projection was simulated using the XCAT digital phantom with differential diaphragm displacement and cardiorespiratory traces acquired from a healthy volunteer. For comparison, each simulation was repeated without tracking. With tracking, treatment margins were reduced by using the target position at end-exhale only. Without tracking, the treatment margin was expanded to encompass the target position over all respiratory phases. In both scenarios, 3mm isotropic margins were used to account for cardiac deformation. Healthy tissue exposure and target coverage were recorded for each projection.

Results: Using tracking and reduced treatment margins, there was a 1.8-, 2.4- and 4.0-fold reduction in mean healthy tissue exposure with diaphragm displacement set to 0.5, 1 and 2cm respectively. Additionally, mean target coverage ranged over 97-99% and 99-100% with and without tracking respectively.

Conclusion: The feasibility of using diaphragm tracking to account for respiratory motion during cardiac radioablation was demonstrated for the first time. This has the potential to transform radiation treatment for cardiac arrhythmias by drastically reducing healthy tissue exposure.

Funding Support, Disclosures, and Conflict of Interest: Authors Hindley and Shieh have submitted a record of invention for the diaphragm tracking technology used in this work.


Heart, Image-guided Therapy, Radiosurgery


IM/TH- RT X-Ray Imaging: CBCT imaging/therapy implementation

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