New energy layer reduction method for rapid intensity-modulated proton therapy (IMPT) using a ridge filter

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Efficient intensity-modulated proton therapy (IMPT) delivery is crucial for treatment effectiveness.
• Reducing energy layers in IMPT delivery accelerates treatment, improves motion management, and enhances accuracy.
• Faster IMPT enables better breath-hold techniques, reducing margins and protecting healthy tissues.

Purpose of the Study:

• Propose a novel method for rapid IMPT by reducing energy layers using a ridge filter.
• Develop an energy layer reduction technique for faster and more accurate proton therapy delivery.

Main Methods:

• Extended the Bragg peak (BP) width using a ridge filter to create an extended Bragg peak (EBP).
• Integrated EBP into an in-house treatment planning system for inverse planning.
• Combined EBP with pristine BP to ensure accurate energy modulation and dose fall-off.
• Formulated an optimization problem with a group sparsity constraint to select BP and EBP energies, solved using a block orthogonal matching pursuit algorithm.

Main Results:

• The combined BP-EBP method significantly reduced energy layers compared to conventional IMPT (e.g., 79 to 28 in an abdomen case, 70 to 30 in a lung case).
• Achieved comparable or slightly better plan quality with the BP-EBP method.
• Reduced IMPT delivery time by over 50% in tested cases.
• Demonstrated the experimental feasibility of the BP-EBP method on a ProteusONE proton therapy system.

Conclusions:

• A novel energy reduction method using BP and EBP generated by a ridge filter was proposed and experimentally validated.
• This technique significantly decreases the number of energy levels required for IMPT.
• The method enhances IMPT delivery efficiency, paving the way for faster and potentially more effective proton therapy treatments.