Reducing PTV margins for prostate SBRT with motion compensation and gating techniques

Area of Science:

• Radiation Oncology
• Medical Physics
• Image-Guided Therapy

Background:

• Prostate stereotactic body radiation therapy (SBRT) requires precise dose delivery.
• Target motion during treatment delivery can compromise dosimetric accuracy.
• Reducing planning target volume (PTV) margins necessitates robust motion management.

Purpose of the Study:

• To investigate the dosimetric accuracy of prostate SBRT considering target motion.
• To evaluate the effectiveness of motion compensation and gating techniques.
• To determine if PTV margins can be reduced with motion management.

Main Methods:

• Utilized a Delta4 phantom, Gafchromic film, and Hexamotion platform for dosimetric measurements.
• Investigated four motion files representing a range of prostate movements.
• Assessed motion compensation and gating techniques against uncorrected deliveries.
• Analyzed five patient plans to study MLC and target motion interplay.

Main Results:

• Motion compensated deliveries achieved an average pass rate of 96.0% (film) vs. 80.5% (uncorrected).
• Gated techniques yielded average pass rates of 94.8% (film) vs. 89.9% (uncorrected).
• Delta4 array analysis showed pass rates of 94.8% (motion compensation) vs. 83.8% (uncorrected).
• Uncorrected motion led to isodose shifts up to 5 mm; compensated/gated techniques minimized these differences.

Conclusions:

• Motion compensation and gating techniques significantly improve prostate SBRT dose delivery accuracy.
• These techniques enable substantial reduction in PTV margins.
• Accurate dose delivery is achievable even with reduced margins when motion is managed.