Linear energy transfer weighted beam orientation optimization for intensity-modulated proton therapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Biophysics

Background:

• Intensity-modulated proton therapy (IMPT) planning faces challenges due to unaccounted biological effectiveness variations, leading to discrepancies between predicted and observed outcomes.
• Accurate modeling of biological doses in treatment planning is crucial for enhancing therapeutic ratios in proton therapy.
• Current methods often overlook the impact of linear energy transfer (LET) on biological effects, necessitating advanced optimization strategies.

Purpose of the Study:

• To develop and evaluate a novel method for incorporating LET into beam orientation optimization (BOO) for intensity-modulated proton therapy (IMPT).
• To improve the accuracy of treatment planning by accounting for biological doses, thereby enhancing the therapeutic ratio.
• To reduce the biological effects on organs at risk (OARs) while maintaining physical dose objectives.

Main Methods:

• A LET-weighted beam orientation optimization (LETwBOO) framework was developed, utilizing the dose-LET product (LET × D) as a biological surrogate.
• The optimization incorporated physical dose fidelity, LET × D constraints for OARs, and group sparsity to reduce beam count from hundreds to 2-4.
• The LETwBOO method was tested on skull base tumor (SBT) and head-and-neck (H&N) cancer patients, comparing plans against manually selected beams (MAN) and reoptimized MAN plans (LETwMAN).

Main Results:

• LETwBOO plans demonstrated superior sparing of OARs in terms of both physical dose and LET × D compared to MAN and LETwMAN plans.
• Average OAR dose reductions in LETwBOO were [2.85, 4.6] GyRBE for SBT and [0.9, 2.5] GyRBE for H&N cases, outperforming LETwMAN.
• LETwBOO achieved greater reductions in OAR LET × D, with average decreases of [1.1, 2.9] Gy for SBT and [0.8, 2.6] Gy for H&N cases compared to MAN.

Conclusions:

• A novel LET-weighted beam orientation optimization (LETwBOO) method for IMPT was successfully developed.
• The LETwBOO method generates treatment plans with significantly improved physical and biological sparing of organs at risk.
• This approach offers a more accurate and effective strategy for IMPT by accounting for biological effects in treatment planning.