Author: Zachary Diamond, Pretesh Patel, Sibo Tian, Xiaofeng Yang, David Yu, Ahmal Jawad Zafar, Jun Zhou 👨🔬
Affiliation: Emory University, Department of Radiation Oncology and Winship Cancer Institute, Emory University 🌍
Purpose:
We propose a method to optimize adaptive proton FLASH therapy (ADP-FLASH) using modularized pin-ridge filters (pRFs) by recycling module pins from the initial plan, reducing pRF adjustments in adaptive FLASH planning.
Methods:
FLASH-pRF plans were created at 250 MeV using pencil beam directions (PBDs) from initial IMPT plans on the planning CT (pCT). PBDs were classified as new/changed (ΔE > 5 MeV) or unchanged by comparing spot maps for targets between pCT and re-CT. An iterative least-square regression model identified recyclable PBDs with minimal relative changes in spot MU weighting. In each iteration, two PBDs with the least error were added to the background plan, while remaining PBDs were reoptimized for the ADP plan in subsequent iterations. Validation was performed on three liver SBRT cases (10Gy×5) by comparing CTV-D95% and duodenum D0.5cc across initial-pRF-plans on pCT, re-CT and the ADP-FLASH-pRF plans on re-CT. FLASH effect was evaluated with a dose and dose rate threshold of 3Gy and 40Gy/s, respectively, using the FLASH effectiveness model.
Results:
The proposed method recycled 91.2%, 71%, and 64.7% of PBDs from initial pRF plans for the three cases. Dosimetric results (CTV-D95% and liver mean dose, in Gy) for initial-pRF-plans on pCT, re-CT, and ADP-FLASH-pRF plans for the three cases were as follows: (92.3%, 83%, 95.2%; 5.2, 3.9, 6.1), (97.3%, 47.9%, 99.2%; 1.3, 0.01, 2.1), (99.9%, 89.5%, 97.1%; 5.0, 4.6, 5.1). For Case 3, duodenum D0.5cc values were 27.1, 32.9, and 28.9, respectively. The ADP-FLASH-pRF plans met clinical goals while preserving FLASH effects across all cases.
Conclusion:
This method efficiently minimizes pRF adjustments in adaptive FLASH planning, achieving comparable dosimetric quality to initial plans while streamlining adaptation in FLASH therapy.