Quantifying the DNA-damaging Effects of FLASH Irradiation With Plasmid DNA

Area of Science:

• Radiation Oncology
• Molecular Biology
• Biophysics

Background:

• Ultrahigh-dose-rate (FLASH) irradiation is an emerging radiotherapy technique.
• Understanding its biological effects, particularly DNA damage, is crucial for clinical translation.
• Conventional dose-rate irradiation causes significant DNA damage.

Purpose of the Study:

• To develop and validate a plasmid DNA nicking assay for quantifying DNA damage from FLASH irradiation.
• To compare the DNA-damaging effects of FLASH irradiation versus conventional dose-rate irradiation.
• To determine the relative biological effectiveness (RBE) of FLASH irradiation for DNA damage.

Main Methods:

• Irradiation of plasmid DNA phantoms at conventional (0.167 Gy/s) and FLASH (46.6 Gy/s, 93.2 Gy/s) dose rates.
• Agarose gel electrophoresis to separate single-strand breaks (SSBs) and double-strand breaks (DSBs).
• Quantitative analysis of DNA damage and calculation of RBE (RBE_SSB, RBE_DSB).

Main Results:

• FLASH irradiation exhibited a sparing effect on DNA, with RBE_SSB and RBE_DSB less than unity.
• DSB RBEs for FLASH beams at 46.6 Gy/s and 93.2 Gy/s were 0.54 ± 0.15 and 0.55 ± 0.17, respectively.
• FLASH irradiation caused demonstrably less DNA damage than conventional dose rates.

Conclusions:

• A DNA-based phantom assay is feasible for assessing FLASH sparing effects.
• FLASH irradiation offers a protective advantage against DNA damage compared to conventional dose rates.
• The protective effect of FLASH irradiation is, at least partially, mediated by fundamental biochemical processes.