Lineal energy-based evaluation of oxidative DNA damage induced by proton beams and X-rays.

PHYSIOLOGICAL effects of protons; PHYSIOLOGICAL effects of x-rays; PHYSIOLOGICAL effects of radiation; PROTON beams; OXIDATION of DNA

Purpose: To determine the oxidative capabilities of proton beams compared to X-rays based on lineal energy ( y). Materials and methods: Microdosimetry was used to determine y-values of 155 MeV protons. Salmon testes deoxyribonucleic acid (ST-DNA) in solution and human tumor cells (MOLT-4) were irradiated with 200 kV X-rays ( X) or 155 MeV protons at their plateau ( P) and near their Bragg-peak ( B). 8-Hydroxydeoxyguanosine (8-OHdG) production was determined by high performance liquid chromatography. Double-strand breaks (DSB) in ST-DNA were evaluated by agarose gel electrophoresis and DSB in cell nuclei were evaluated by immunocytochemical analysis of phosphorylated histone H2AX (γH2AX) foci. Edaravone was used as a radical scavenger. Results: 8-OHdG yields in ST-DNA were significantly higher with X than with P or B, and they were significantly higher with P than with B. DSB yields in ST-DNA were higher with P than with B or X, although not statistically significant, and were nearly equal with B and X. Although γH2AX foci formation in MOLT-4 cells after each irradiation type was nearly identical, the addition of edaravone significantly inhibited foci formation only with X. Conclusions: Our results indicated that radical-induced indirect DNA damage was significantly lower with proton beams than with X-rays. [ABSTRACT FROM AUTHOR]