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AlignRT as a Respiratory Motion Management Tool for SBRT
- 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.
Editor's Notes
- SBRT was initially developed for treatment of early-stage lung cancer in medically inoperable patients SBRT remains investigational as an acceptable alternative to surgery in operable patients (controversial point) This discussion will focus on the use of SBRT in lung and liver tumors
- Internal Target Volume – a volume that encompasses the CTV in ALL phases of the respiratory cycle. Respiratory Gating – administration of radiation within a particular portion of the patient’s breathing cycle, which is determined by monitoring the patient’s respiratory motion, typically using an external fiducial marker (e.g. Varian RPM system)