Streamlined pin-ridge-filter design for single-energy proton FLASH planning

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• FLASH radiotherapy (FLASH-RT) utilizes ultra-high dose rates to decrease normal tissue toxicity while preserving tumor control.
• Single-energy proton beams modulated by ridge filters (RFs) are a feasible approach for FLASH-RT planning.

Purpose of the Study:

• To investigate the feasibility of a streamlined, sparsely pinned pin-shaped RF (pin-RF) design for single-energy proton FLASH planning.

Main Methods:

• Developed an inverse planning framework integrating treatment planning system capabilities.
• Generated multi-energy proton plans using intensity-modulated proton therapy (IMPT) with a downstream energy modulation strategy (IMPT-DS).
• Translated IMPT-DS plans to single-energy IMPT-RF plans using a spot reduction process and validated on three lung cases.

Main Results:

• IMPT-RF plans closely matched IMPT-DS plans in dose conformity with minimal changes in lung V7Gy/V7.4Gy.
• Significant reductions (up to 33%) in maximum dose (Dmax) for normal structures in high-to-moderate dose regions were observed.
• Positive clinical benefits were noted, with Dmax reductions of 21.4%-33.0% for healthy tissues in high-dose regions, though marginal benefits were seen in lower dose areas.

Conclusions:

• A streamlined pin-RF design is effective for single-energy proton FLASH planning, demonstrating clinical benefits for normal tissues in high-dose areas.
• The simplified pin-RF design offers potential advantages in cost-efficiency and ease of production, making it a promising radiotherapy tool.