Investigation of FLASH Proton Radiation Induced DNA Double Strand Breaks in Plasmid DNA Using Atomic Force Microscopy

Area of Science:

• Radiation Oncology
• Molecular Biology
• Biophysics

Background:

• Understanding DNA damage mechanisms is crucial for radiation therapy.
• FLASH and conventional dose rate (CDR) radiation exhibit different biological effects.
• Free radical scavengers modulate radiation-induced DNA damage.

Purpose of the Study:

• To investigate the influence of free radical scavenger concentration, radiation dose, and linear energy transfer (LET) on DNA double-strand breaks (DSBs) induced by FLASH proton radiation.
• To compare DNA damage from FLASH and CDR proton radiation using a cell-free plasmid DNA model.

Main Methods:

• Utilized atomic force microscopy (AFM) to quantify DSBs in pUC-19 plasmid DNA.
• Irradiated DNA with FLASH and CDR proton beams at varying doses (1-3 kGy) and beam regions (plateau, Bragg peak).
• Assessed DNA damage under different HEPES buffer concentrations (2 mM and 10 mM) as a free radical scavenger.

Main Results:

• FLASH proton radiation consistently induced fewer DSBs than CDR at 2 mM HEPES concentration.
• At 10 mM HEPES, FLASH showed fewer DSBs at 1 kGy but more DSBs than CDR at 3 kGy.
• DSBs per plasmid were higher at the Bragg peak than plateau at 2 mM HEPES; this was dose-rate dependent at 10 mM HEPES.

Conclusions:

• AFM provides nanometer-scale benchmarks for comparing FLASH and CDR radiation effects on DNA.
• FLASH radiation's protective effect against DSBs is concentration- and dose-dependent.
• Initial DNA damage from FLASH radiation results from a synergistic interaction between radical chemistry, dose, and LET.