Proton therapy delivery method affects dose-averaged linear energy transfer in patients

Area of Science:

• Medical Physics
• Radiation Oncology
• Biophysics

Background:

• Proton therapy offers dosimetric advantages, leading to widespread adoption.
• Technological advancements have shifted proton delivery from passive scattering (PS) to pencil-beam scanning (PBS).
• Biological effectiveness of proton dose is linked to linear energy transfer (LET_D).

Purpose of the Study:

• To investigate how different proton delivery methods (PS vs. PBS) influence dose-weighted average linear energy transfer (LET_D).
• To compare LET_D distributions within and outside target volumes for PS and PBS plans in clinical scenarios.

Main Methods:

• Utilized the TOPAS Monte Carlo transport code to simulate simple, dosimetrically matched, and clinical treatment plans.
• Simulated single-field plans in a water phantom for both PS and PBS.
• Analyzed treatment and anatomic data from pediatric craniopharyngioma patients treated with PS or PBS proton therapy.

Main Results:

• PBS delivery resulted in significantly higher LET_D values compared to PS, both within and outside the target volume (p < 0.01 for simple plans).
• LET_D was generally greater for PBS treatment plans than for PS plans in matched and clinical scenarios (p < 0.05).
• LET_D distributions differed significantly between PS and PBS delivery methods in clinically relevant regions.

Conclusions:

• The method of proton delivery significantly affects LET_D, both inside and outside the target volume.
• Findings suggest PBS is biologically more effective than PS due to higher LET_D.
• Further research is crucial to adapt existing treatment evaluation methods for PBS to ensure safety and efficacy for the growing patient population.