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Abstract
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.
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Acknowledgements
We are indebted to Mr Masaru Sato, Mr Masaya Ishida and Ms Junko Zenkoh for their competent technical assistance and for preparation of this manuscript.
Declaration of interest The authors report no declaration of interest. The authors alone are responsible for the content and writing of the paper.
This work was partly supported by a Grant-in-Aid (grant number: 20390323) from the Ministry of Education, Culture, Sports, Science & Technology of Japan.