Implementation of apertures in a proton pencil-beam dose algorithm.

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Modeling

Background:

• Field-specific apertures are crucial in proton therapy for sharpening beam edges, especially in pencil-beam scanned (PBS) delivery.
• Existing methods for PBS may not fully capture the impact of apertures, particularly at low energies or high doses.
• Accurate modeling of apertures is necessary for optimizing PBS clinical implementation.

Purpose of the Study:

• To develop and validate a computational model for simulating the effect of shaped apertures in pencil-beam scanned proton therapy.
• To investigate the physical contributions to penumbra and nuclear halo formation when using apertures in PBS.
• To enable the full clinical deployment of PBS capabilities by accurately accounting for aperture physics.

Main Methods:

• A novel model was implemented within a clinical pencil-beam algorithm, decomposing spot transport into discrete steps.
• The model simulates primary scattering through the patient and range shifter, followed by aperture modulation.
• An efficient Clarkson sector integration method was used for modeling nuclear scattered halo protons.

Main Results:

• The model demonstrates that in-patient and shifter scattering are the primary contributors to the aperture effect in PBS.
• A small contribution from the apparent beam source position to the penumbra was identified.
• The developed model provides insights into the physics governing penumbra and nuclear halo in PBS with apertures.

Conclusions:

• The implemented model accurately simulates aperture effects in PBS, crucial for clinical application.
• This modeling advancement allows for the effective utilization of PBS technology, potentially improving treatment outcomes.
• The model enhances understanding of fundamental physics in proton beam delivery, bridging computational and clinical observations.