April 2009 references and further reading
Radiation in medicine: A double-edged sword
Health Physics Society. Naturally occurring radiation.
Mettler FA, Jr., Bhargavan M, Thomadsen BR, et al. Nuclear medicine exposure in the United States, 2005-2007: preliminary results. Seminars in Nuclear Medicine 2008; 38:384-91.
Mettler FA, Jr., Thomadsen BR, Bhargavan M, et al. Medical radiation exposure in the U.S. in 2006: preliminary results. Health Physics 2008; 95:502-7.