Incorporating variable RBE in IMPT optimization for ependymoma.

Area of Science:

• Medical Physics
• Radiation Oncology
• Biophysics

Background:

• Intensity-modulated proton therapy (IMPT) is an advanced radiation technique.
• Relative biological effectiveness (RBE) of protons can vary depending on factors like linear energy transfer (LET).
• Accurate RBE modeling is crucial for optimizing proton therapy plans.

Purpose of the Study:

• To assess the dosimetric impact of variable proton RBE in IMPT.
• To compare variable RBE optimization with constant RBE and LET-based methods.
• To evaluate optimization strategies for pediatric ependymoma treatment.

Main Methods:

• Four optimization strategies were compared in 10 pediatric ependymoma patients: constant RBE, LET-based, variable RBE, and hybrid RBE.
• Plans were normalized for target coverage.
• Dose, dose-averaged LET (LETd), LET-weighted dose, and equivalent uniform dose were analyzed.

Main Results:

• LET-based optimization increased LET in targets and maintained or decreased it in critical organs.
• Variable RBE optimization reduced mean and maximum doses in the brainstem and spinal cord.
• Hybrid RBE optimization achieved higher target doses and reduced high RBE in critical tissues compared to other methods.

Conclusions:

• Direct incorporation of variable RBE models into IMPT optimization is feasible.
• A hybrid RBE optimization strategy shows clinical potential for ependymoma treatment.
• This approach can maintain dose limits while minimizing high RBE in normal tissues.