Using the ICD lead as a tracking surrogate for cardiac radioablation: impact of cardiac motion
MO-0474
Abstract
Using the ICD lead as a tracking surrogate for cardiac radioablation: impact of cardiac motion
Authors: Louis Rigal1, Julien Bellec2, Aurélien Hervouin2, Mathieu Lederlin3, Karim Benali4, Raphaël Martins5, Renaud De Crevoisier6, Antoine Simon1
1Université Rennes 1, LTSI - Inserm 1099, Rennes, France; 2CLCC Eugène Marquis, Medical Physics Department, Rennes, France; 3CHU Rennes, Radiology and Medical Imaging Department, Rennes, France; 4Saint-Etienne University Hospital, Department of Cardiology, Saint-Priest-En-Jarez, France; 5CHU Rennes, Department of Cardiology, Rennes, France; 6CLCC Eugène Marquis, Radiation Therapy Department, Rennes, France
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Purpose or Objective
Cardiac
radioablation is a promising application of stereotactic body radiotherapy for
patients with refractory ventricular tachycardias (VT). The Implantable
Cardioverter Defibrillator (ICD) lead is often used as a surrogate when using
an active respiratory motion technique. However, the ICD lead and the target
volume may present motion discrepancies during the cardiac cycle. These
uncertainties should then be considered when defining the planning target
volume. The objectives of this study were to evaluate: (i) the reliability of
the ICD lead to track the target position along the cardiac cycle; (ii) the
geometrical impact of these tracking uncertainties on the target volume.
Material and Methods
Contrast-enhanced
breath-hold cardiac computed tomography (c4D-CT) of 16 patients were acquired
and reconstructed in 10 3D images datasets. The arrhythmogenic substrate,
defined as the Clinical Target Volume (CTV), was delineated on one phase of
each c4D-CT dataset. The CTV was then propagated to all other phases using
deformable image registration. The centroid coordinates of the propagated CTV,
which were considered as the position of the CTV, were reported for each c4D-CT
phase. The successive positions of the ICD lead were also reported by manually locating
the tip of the ICD lead in each c4D-CT phase.
CTV and ICD
lead motions discrepancies were evaluated by calculating the Mean Absolute
Error (MAE) between their displacement vectors. The correlation between MAE and
the ICD lead-to-CTV distance (d) was evaluated by computing the Pearson
Correlation Coefficient (PCC).
To evaluate
the geometrical impact of the motion discrepancies on the target volume, all
phases were registered by considering the ICD lead static. A synchronization
ITV (ITVsync) was then defined as the union of the propagated CTVs.
Results
MAE and d
values are reported in figure 1.
The mean
(min - max) MAE was of 3.2 (1.4 - 4.9) mm. The mean (min - max) d value was 66
(19 – 120) mm. No correlation was found between MAE and d (PCC = 0.28).
The CTV and
ITVsync are reported in figure 2. The ITVsync represented
a mean (min – max) relative increase of the CTV of 101 (39 – 151) %.
Conclusion
In cardiac
radioablation of VT, large discrepancies between cardiac-induced motions of the
ICD lead and CTV occur. Integrating these errors requires doubling the target
volume on average.