Stereotactic Ablative Radiotherapy of Ventricular Tachycardia Using Tracking: Optimized Target Definition Workflow

Area of Science:

• Medical Physics
• Radiation Oncology
• Cardiology

Background:

• Stereotactic arrhythmia radioablation (STAR) offers an alternative for ventricular tachycardias post-catheter ablation in structural heart disease.
• The CyberKnife system is a platform for STAR, using target tracking technology.
• Tracking accuracy can be compromised by deformation between the implantable cardioverter-defibrillator (ICD) lead tip marker and the actual target.

Purpose of the Study:

• To propose a simple method to account for marker-target geometry deformation in STAR.
• To improve the accuracy of target definition for CyberKnife-based STAR treatments.

Main Methods:

• A Geometry Deformation Margin (GDM) method was developed to expand the clinical target volume (CTV) into an internal target volume (ITV).
• CT scans acquired at different respiratory phases were used to calculate anisotropic GDM based on triple registration.
• GDM-based target volumes were compared to original planning target volumes (PTVs) and volumes generated using deformable image registration (DIR) software.

Main Results:

• The GDM method accounts for marker-target deformation, creating larger target volumes shifted towards the inspiration phase compared to non-deformation-corrected volumes.
• GDM-based target volumes showed high similarity (DICE 0.80-0.87) to those generated by DIR software.
• Image registration observer variability was covered by a 2 mm margin.

Conclusions:

• The proposed GDM method is a straightforward approach to manage marker-target deformation uncertainty in STAR.
• This method enhances tracking accuracy with CyberKnife and reduces the risk of target underdose.
• The GDM principle is applicable to general radiotherapy procedures.