Planar Proton Minibeam Irradiation Elicits Spatially Confined DNA Damage in a Human Epidermis Model

Purpose: High doses of ionizing radiation in radiotherapy can elicit undesirable side effects to the skin. Proton minibeam radiotherapy (pMBRT) may circumvent such limitations due to tissue-sparing effects observed at the macro scale. Here, we mapped DNA damage dynamics in a 3D tissue context at the sub-cellular level. Methods: Epidermis models were irradiated with planar proton minibeams of 66 mu m, 408 mu m and 920 mu m widths and inter-beam-distances of 2.5 mm at an average dose of 2 Gy using the scanning-ion-microscope SNAKE in Garching, GER. gamma-H2AX + 53BP1 and cleaved-caspase-3 immunostaining revealed dsDNA damage and cell death, respectively, in time courses from 0.5 to 72 h after irradiation. Results: Focused 66 mu m pMBRT induced sharply localized severe DNA damage (pan-gamma-H2AX) in cells at the dose peaks, while damage in the dose valleys was similar to sham control. pMBRT with 408 mu m and 920 mu m minibeams induced DSB foci in all cells. At 72 h after irradiation, DNA damage had reached sham levels, indicating successful DNA repair. Increased frequencies of active-caspase-3 and pan-gamma-H2AX-positive cells revealed incipient cell death at late time points. Conclusions: The spatially confined distribution of DNA damage appears to underlie the tissue-sparing effect after focused pMBRT. Thus, pMBRT may be the method of choice in radiotherapy to reduce side effects to the skin.

Automated summary

Proton minibeam radiotherapy (pMBRT) can achieve tissue-sparing effects at the sub-cellular level, reducing side effects to the skin, and successfully repairing DNA damage.