An analytical dose-averaged LET calculation algorithm considering the off-axis LET enhancement by secondary protons...

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Biology

Background:

• Accurate calculation of dose-averaged linear energy transfer (LETd) is crucial for assessing biological effects in proton therapy.
• Existing analytical methods may not fully capture the complexities of LETd distribution, particularly off-axis effects.

Purpose of the Study:

• To develop and validate an analytical method (PBA-dLET) for fast and accurate LETd calculation in proton therapy.
• To incorporate the off-axis enhancement of LETd due to secondary protons into a pencil-beam algorithm (PBA).

Main Methods:

• Developed a dual-LET-kernel model within the PBA framework, assigning separate LET values for primary and halo components.
• Utilized a triple Gaussian model for dose kernels, accounting for primary protons and secondary protons from nuclear reactions.
• Validated the PBA-dLET algorithm against Monte Carlo simulations (MCS) in homogeneous phantoms and complex patient geometries (prostate, liver, lung).

Main Results:

• The PBA-dLET method demonstrated good agreement with MCS results for LETd profiles in both phantom and patient geometries.
• Excellent accuracy was observed, with maximum differences in mean LETd (LETd,mean) below 0.08 keV/μm compared to MCS.
• Significant improvement in accuracy was noted at the lateral penumbra compared to single-LET-kernel models.

Conclusions:

• The developed dual-LET-kernel model accurately reproduces LETd distributions calculated by MCS in various geometries.
• This method offers improved accuracy for LETd calculations in proton therapy, particularly in complex anatomical regions.
• The PBA-dLET model is valuable for precise risk assessment of side effects in proton therapy, especially when targets are near critical organs.