Updated information is given on alpha-particle-induced
cancer in persons internally exposed to 222Rn progeny,
Thorotrast, long-lived 226Ra and 228Ra, and short-lived 224Ra. The
lung cancer risk to persons breathing 222Rn progeny in the indoor air of offices, schools, and homes is of increasing concern. About half of the recent deaths among the German
Thorotrast patients have been from
liver cancer. Animal studies indicate that the
liver cancer risk from
Thorotrast is mainly from its radioactivity and that the risk coefficient for the
Thorotrast patients can be used provisionally for other alpha emitters in the human liver. Six skeletal
cancers have occurred in persons with average skeletal doses between 0.85 and 11.8 Gy from 226Ra and 228Ra. In the low-dose German 224Ra patients, two skeletal
sarcomas have occurred at about 0.7 Gy compared to about six cases predicted by results from 224Ra patients at higher doses. The minimal appearance time for radiation-induced bone
sarcomas in humans is about 4 y. Following brief irradiation, the vast majority of induced bone
sarcomas are expressed by about 30 y. Recent evidence against the "practical threshold" hypothesis is given. With the downward revision of neutron doses to the atomic-bomb survivors, the follow-up of persons exposed to alpha particles may be the best opportunity to evaluate directly the effects of high LET radiation on humans.