Development of an algorithm for proton dose calculation in magnetic fields.

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Imaging

Background:

• Proton therapy offers advantages that can be amplified by integrating online magnetic resonance imaging (MRI) guidance.
• A significant hurdle in implementing MRI-guided proton therapy (MRPT) is the precise calculation of radiation dose within magnetic fields.

Purpose of the Study:

• To develop an efficient and accurate algorithm for calculating proton dose in the presence of magnetic fields.

Main Methods:

• Developed the Proton and Ion Dose Engine (PRIDE), an analytical-numerical algorithm combining the pencil beam algorithm (PBA) with iterative voxel-based ray-tracing.
• Validated PRIDE's accuracy against Monte Carlo (MC) simulations on phantoms and practical treatment plans across magnetic field strengths up to 3.0 T.
• Employed global gamma index criteria (2%/2 mm and 3%/3 mm) for quantitative comparison.

Main Results:

• PRIDE demonstrated excellent agreement with MC simulations (gamma passing rates >99% for 2%/2 mm at 1.5 T) in homogeneous and slab heterogeneous phantoms.
• Accuracy remained high (>98% for 2%/2 mm) even at 3.0 T and 240 MeV, despite a slight decrease.
• Practical plans in varying magnetic fields achieved >98% and >99% passing rates for 2%/2 mm and 3%/3 mm criteria, respectively.

Conclusions:

• The PRIDE algorithm provides efficient and accurate proton dose calculations in magnetic fields up to 3.0 T.
• PRIDE is poised to be a valuable tool for dose calculation in MRI-guided proton therapy (MRPT).