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

Monolayers of human lymphocytes, attached to a 2-mum Mylar film, were irrad iated with 60 kV X rays in the presence and absence of a 150-mum gold film backing the Mylar film. With the gold film present, the absorbed dose impar ted to the cells was increased by a factor of 45.4 due to the release of ph otoelectrons from the gold film. The frequencies of dicentric chromosomes a nd 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 c ompared to the frequencies observed in the absence of the gold film was fou nd. These radiation effects, which contribute to risk consideration in radi ology, are interpreted in terms of the increased dose-mean restricted LET o f the photoelectrons back-scattered from the metal and slowed down in the M ylar film before they enter the cell layer. (C) 2001 by Radiation Research Society.