Patient-specific collision zones for 4π trajectory optimized radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Imaging

Background:

• The 4π methodology optimizes noncoplanar arcs for stereotactic radiation therapy (SRT) to minimize dose to organs-at-risk.
• Applying 4π to stereotactic body radiation therapy (SBRT) is challenging due to unknown collision zones between the gantry, couch, and patient.
• Patient-specific collision zones are crucial for safe and effective noncoplanar SBRT.

Purpose of the Study:

• To develop and validate a system for determining patient-specific collision zones in SBRT.
• To enable safe and deliverable noncoplanar treatment trajectories for SBRT patients.
• To overcome the barrier posed by unknown collision zones in 4π SBRT.

Main Methods:

• Augmented patient CT scans with full-body optical scans to create patient models.
• Registered library scans to patient CTs and added couch/immobilization models.
• Aligned patient models in a virtual treatment room with the LINAC to test for collisions.

Main Results:

• The collision detection algorithm demonstrated high accuracy (97.80%) and sensitivity (99.99%).
• A 6 cm buffer was required for the registration algorithm to achieve 99.65% mean sensitivity.
• The system achieved 86.70% mean accuracy and 99.33% mean NPV with the buffer.

Conclusions:

• Patient-specific collision zones can be determined with minimal user intervention using an a priori library of body surface scans.
• This method facilitates the safe application of 4π SBRT.
• The developed system enables personalized and safe noncoplanar treatment planning.