Quantifying Allowable Motion to Achieve Safe Dose Escalation in Pancreatic SBRT

Area of Science:

• Radiation Oncology
• Medical Physics
• Gastrointestinal Oncology

Background:

• Tumor motion significantly impacts the safety and efficacy of pancreatic stereotactic body radiation therapy (SBRT).
• Accurate motion assessment is crucial for optimizing treatment delivery and managing potential toxicities.

Purpose of the Study:

• To establish patient-specific motion magnitude limits for safe pancreatic SBRT delivery.
• To guide motion management decisions, particularly in scenarios involving dose escalation.
• To analyze the interplay between tumor motion, radiation dose, and tumor volume.

Main Methods:

• Utilized 91 datasets of pancreatic tumor motion data from 25 patients.
• Calculated motion-convolved doses for the gross tumor volume, duodenum, and stomach.
• Developed linear/quadratic models to define maximum allowable motion based on dose metrics and error thresholds.

Main Results:

• Mean allowable motion at 33, 40, and 50 Gy was 11.9, 10.4, and 9.0 mm, respectively.
• Maximum allowable motion decreased with dose escalation and was smaller for larger tumors.
• Significant inter-plan variability in allowable motion suggests patient-specific motion management is feasible.

Conclusions:

• Pancreatic SBRT motion effects are patient-specific, allowing for potentially greater motion in some cases, even with dose escalation.
• A conservative motion limit of 6.3 mm is safe for all patients receiving 33 Gy in 5 fractions.
• Individualized motion assessment can optimize pancreatic SBRT delivery and potentially enable dose escalation.