Biomedical Engineering Reference
In-Depth Information
13.7
Sources of Human Data
A considerable body of data exists on radiation effects on man. Risks for certain
deleterious effects are reasonably well established at high doses, well above rec-
ommended limits. Without attempting to be complete, we mention some of the
important sources of data on humans to indicate their scope and the kinds of ef-
fects encountered. For many years (into the 1950s), the genetic effects of radiation
were considered to pose the greatest danger for human populations exposed to low
levels of radiation. Today, the major concern is cancer.
The Life Span Study
The most important source of information on the effects of ionizing radiation
on humans is the continuing Life Span Study of long-term health effects in the
atomic-bomb survivors at Hiroshima and Nagasaki. The work is conducted by the
joint Japanese/United-States Radiation Effects Research Foundation
1)
(RERF). Its
objectives include the assessment and characterization of differences in life span
and causes of death among the atomic-bomb survivors compared with unexposed
persons. Incidence and mortality data are obtained from vital-statistics surveys,
death certificates, and other sources. The original sample for the study consisted
of about 120,000 persons from among approximately 280,000 identified at the time
of the 1950 census as having been exposed to the weapons. Included were a core
group of survivors exposed within 2 km of ground zero, other survivors exposed
out to distances where little radiation was received, and non-exposed individuals.
The sample was eventually constructed by sub-sampling to include all members of
the core group and equal-sized samples from the other two, matched by age and
sex. Various special cohorts have been formed to study particular questions.
A major task was undertaken to assign doses retrospectively to organs of each
individual survivor. Doses were based on analysis of what was known about the
weapons' output and the location and shielding of the individual. A number of
measurements were conducted at the Nevada Test Site and elsewhere in support of
this work. By 1965, a tentative dosimetry system, T65D, was in place for estimating
individual doses. This systemwas substantially updated by the 1986 revision, DS86.
The basic quantities determined included the gamma and neutron contributions to
the free-in-air kerma and the shielded kerma as functions of the ground distance
from the detonations. Doses to different tissues and organs were estimated for
individual survivors.
Certain discrepancies persisted between some DS86 predictions when compared
with important markers. For example, differences were found between calculated
neutron activation products and the activity measured in materials actually ex-
posed at different distances to the bomb radiation. (Activation products include
1
Formally called the Atomic Bomb Casualty
Commission.
