Detection of elevated RBE in human lymphocytes exposed to secondary electrons released from X-irradiated metal surfaces.

Regulla, D., Panzer, W., Schmid, E., Stephan, G. and Harder, D. Detection of Elevated RBE in Human Lymphocytes Exposed to Secondary Electrons Released from X-Irradiated Metal Surfaces. Radiat. Res. 155, 744-747 (2001). Monolayers of human lymphocytes, attached to a 2-microm Mylar film, were irradiated with 60 kV X rays in the presence and absence of a 150-microm gold film backing the Mylar film. With the gold film present, the absorbed dose imparted to the cells was increased by a factor of 45.4 due to the release of photoelectrons from the gold film. The frequencies of dicentric chromosomes and centric rings as well as of excess acentric fragments were increased in agreement with this dose enhancement, and in addition an RBE of about 1.7 compared to the frequencies observed in the absence of the gold film was found. These radiation effects, which contribute to risk considerations in radiology, are interpreted in terms of the increased dose-mean restricted LET of the photoelectrons backscattered from the metal and slowed down in the Mylar film before they enter the cell layer.