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Additional resources for Effects of Ionizing Radiation: United Nations Scientific Committee on the Effects of Atomic Radiation: UNSCEAR 2006 Report to the General Assembly With Scientific Annexes C, D, and (Official Records), Vol. II

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Despite the caveats outlined above, there are studies indicating a bystander effect in vivo. Chinese hamsters were injected with different sized particles of the internally deposited alpha emitter plutonium. The radioactive particles concentrate in the liver and produce chronic low-dose radiation exposure, with the dose and dose rate being highest to cells located closest to the largest particles. However, analysis of induced chromosome damage in these livers revealed increased cytogenetic damage that was not directly related to the local dose distribution [B17].

An abscopal effect may be defined as a significant ­tissue response to irradiation in tissues definitively separate from the region exposed to radiation. The response must be measurable, and the distance separating the responding ­tissues and the portal(s) of irradiation must be great enough to rule out any possible effect of scattered radiation [N15]. Originally described by Mole [M52] in 1953, the word abscopal comes from the Latin ab (position away from) and scopus (mark or target). The mechanism of the abscopal effect is unknown, although a variety of underlying biological events can be hypothesized, including a possible role for the immune system [M46, U24].

This observation was later confirmed and extended by Lehnert and co-workers [D2, L2]. The induced sister chromatid exchanges could be inhibited by superoxide dismutase, once again indicating a role for ROS [L2, N8, N9]. The alpha-particleinduced increase in ROS appears to be temporally linked to enhanced production of tumour necrosis factor alpha and interleukin 1, which in turn operate in an autocrine manner to up-regulate interleukin 8 [N9]. Low fluences of alpha particles can also increase mutation yield [N5] and cause accumulation of the tumour suppressor protein TP53 in a higher percentage of the exposed population than calculated to receive a nuclear traversal by one or more alpha particles [H5].

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