Dose response and kinetics of foci disappearance following exposure to high- and low-LET ionizing radiation

Abstract

Purpose: The effect of different radiation qualities on (i) 53BP1 (p53 Binding Protein 1) and p-ATM (phosphorylated ataxia telangiectasia mutated) foci induction, and (ii) on the kinetics of foci disappearance was analysed.

Material and methods: Normal human skin fibroblasts were exposed to 240 kV broad-field X-rays or targeted with individually counted helium (³He) particles or protons (¹H) from a Charged Particle Microbeam. Anti-p-ATM and anti-53BP1 antibodies were used for foci visualisation via immunocytochemistry.

Results: 1 Gy of X-rays yielded ≈ 33 53BP1-positive foci/cell. The ratio between the number of delivered particles and yielded tracks was found to be 1:1 and 3:1 after targeted ³He and ¹H irradiation, respectively. It was determined that ≈ 50% of radiation-induced damage was repaired as measured by loss of foci during the first 2, 6, and 10 hours following X-ray, protons, and ³He irradiation, respectively.

Conclusions: There was significant radiation quality dependence for 53BP1- and p-ATM-positive foci induction observed. Foci disappearance was radiation dose-independent in the samples irradiated with X-rays. Our results confirm that kinetics of foci disappearance depends on radiation quality, even when individual ions are targeted to cells.

Keywords:

• kinetics of foci disappearance
• protons
• X-rays
• microbeam
• ³He particles