Characterisation of a setup for mixed beam exposures of cells to 241Am alpha particles and X-rays

Abstract

Exposure of humans to mixed fields of high- and low-linear energy transfer (LET) radiation occurs in many situations-for example, in urban areas with high levels of indoor radon as well as background gamma radiation, during airplane flights or certain forms of radiation therapy. From the perspective of health risk associated with exposure to mixed fields, it is important to understand the interactions between different radiation types. In most cellular investigations on mixed beams, two types of irradiations have been applied sequentially. Simultaneous irradiation is the desirable scenario but requires a dedicated irradiation facility. The authors have constructed a facility where cells can be simultaneously exposed to (241)Am alpha particles and 190-kV X-rays at 37°C. This study presents the technical details and the dosimetry of the setup, as well as validates the performance of the setup for clonogenic survival in AA8 Chinese hamster ovary cells. No significant synergistic effect was observed. The relative biological effectiveness of the alpha particles was 2.56 for 37 % and 1.90 for 10 % clonogenic survival.

Gamma-H2AX foci in cells exposed to a mixed beam of X-rays and alpha particles

“…In the setups applied by us and Franken et al [50] one particle track could only be viewed as a singe IRIF, which led to an underestimation of the number of IRIF after alpha particles and thereby the RBE. Previously, alpha particle RBE values of 2.57 and 1.90 for 37% and 10% clonogenic survival in AA8 cells and 3.2 for micronuclei in human peripheral blood lymphocytes have been observed using this setup [45,46]. The dose response of mixed beam-irradiated cells was intermediate to that of X-ray and alpha particle-irradiated cells, and the differences in repair kinetics between observed and predicted for the first 3 time points were non-significant (Figure 2C-D).…”

“…The discs were custom-constructed in the Institute for Energy-JRC, Petten, Netherlands according to a design based on Edwards et al [63], and are described in detail in Staaf et al [45]. Before exposure the discs were cleaned with 70% ethanol and kept for 1 h in a 37°C incubator.…”

“…The mixed beam exposure facility MAX consists of an incubator, with the alpha irradiator AIF 08 positioned inside and an X-ray tube positioned underneath [45]. The alpha particle exposure facility was constructed in the Institute of Nuclear Chemistry and Technology, Warszawa, Poland and incorporates a 241 Am source (AP1 s/n 101, Eckert and Ziegler, Berlin, Germany) and a movable shelf for positioning cells on the PA discs at discrete distances from the source.…”

“…The fluence and LET of alpha particles was measured with the help of a PADC (polyallyl diglycol carbonate) track-etched detector [64] and was 23789 ± 4564 particles per second per cm 2 [45]. …”

“…We have recently developed a dedicated exposure facility that allows studying the cellular effects of mixed beam exposure [45]. The facility allows a simultaneous irradiation of cells with alpha particles from above and X-rays from below and we use it to investigate the formation and disappearance of IRIF in cells exposed to mixed beams.…”