This document discusses the use of AlignRT as a tool for managing respiratory motion during stereotactic body radiation therapy (SBRT). It notes that SBRT requires very accurate targeting to minimize risks, but respiratory motion can cause targeting errors if not addressed. Several methods for managing motion are described, including internal target volume expansion, respiratory gating, and breath hold techniques. The document indicates that deep inspiration breath hold may be optimal as it eliminates motion without relying on 4D imaging, but reproducibility is challenging. It then describes how AlignRT can help ensure reproducible deep inspiration breath holds are achieved during SBRT treatment planning and delivery.

1. AlignRT® as a Respiratory Motion
Management Tool for SBRT
David Marcus, MD
ASTRO Annual Meeting 2015

2. SBRT Applications
• Early stage lung cancer
– Medically inoperable or borderline operable
patients
– Operable patients
• Lung metastases
• Liver metastases
• Spine metastases
• Prostate

3. The Problem of Respiratory Motion
• Characteristics of SBRT
– High dose per fraction
– Heterogeneous dose distributions within the PTV
– Rapid dose fall-off outside of the PTV
• Accurate targeting of the PTV is critical!
• Failure to reliably address respiratory motion
could result in a potentially catastrophic
marginal miss.

4. Management of Respiratory Motion
• 4-dimensional CT
– Internal Target Volume (ITV)
– Respiratory Gating
• Breath hold methods
– Deep Inspiration Breath Hold
– Active Breathing Control
• Forced Shallow Breathing
– Abdominal Compression

5. Management of Respiratory Motion
• ITV Approach
– Pros:
• PTV covers tumor location in all phases of respiratory
cycle
– Cons:
• 4-D CT scan may be affected by variations in respiratory
patterns during acquisition
• Larger PTV  more dose to OARs

6. Management of Respiratory Motion
• Respiratory Gating
– Pros:
• Can treat smaller volume than with ITV approach
– Cons:
• Relies on accurate 4-D CT and reproducible placement
of external fiducial marker
• End-user doesn’t control beam on/off
• Longer treatment time compared to non-gated
procedure

7. Management of Respiratory Motion
• Deep Inspiration Breath Hold (DIBH) may
represent the best of both worlds…
– Eliminates respiratory motion
– Does not rely on accurate 4-D CT capture
– Smaller volume than with ITV approach
• The major challenge with DIBH is
reproducibility.

8. AlignRT®  Reproducible DIBH
• SBRT Workflow with AlignRT®
– Patient set up according to skin tattoos
– Orthogonal kV imaging during DIBH  apply shifts
– Recapture AlignRT® reference surface within same DIBH
– Acquire Cone Beam CT with DIBH
• AlignRT to verify and monitor DIBH
– Apply shifts
– Recapture AlignRT® reference surface within same DIBH
– Deliver treatment with DIBH
• AlignRT® to verify and monitor DIBH

9. Conclusions
• AlignRT® is a simple but ultimately quite
useful tool for ensuring a reproducible DIBH in
the setting of SBRT.
• AlignRT® is easily incorporated into the SBRT
workflow.