DNA double strand breaks in the acute phase after synchrotron pencilbeam irradiation

Introduction. At the biomedical beamline of the European Synchrotron Radiation Facility (ESRF), we have established a method to study pencilbeam irradiation in-vivo in small animal models. The pencilbeam irradiation technique is based on the principle of microbeam irradiation, a concept of spatially fractionated high-dose irradiation. Using gamma H2AX as marker, we followed the development of DNA double strand breaks over 48 hrs after whole brain irradiation with the pencilbeam technique. Method. Almost square pencilbeams with an individual size of 51 x 50 mu m were produced with an MSC collimator using a step and shoot approach, while the animals were moved vertically through the beam. The center-to-center distance (ctc) was 400 mu m, with a peak-to-valley dose ratio (PVDR) of about 400. Five groups of healthy adult mice received peak irradiation doses of either 330 Gy or 2,460 Gy and valley doses of 0.82 Gy and 6.15 Gy, respectively. Animals were sacrificed at 2, 12 and 48 hrs after irradiation. Results. DNA double strand breaks are observed in the path of the pencilbeam. The size of the damaged volume undergoes changes within the first 48 hours after irradiation. Conclusions. The extent of DNA damage caused by pencilbeam irradiation, as assessed by H2AX antibody staining, is dose-dependent.