An epidemiological assessment of lens opacifications that impaired vision in patients injected with radium-224

The incidence of lens opacifications that impaired vision
(cataract) was analyzed among 831 patients who were injected with
known dosages of 224Ra in Germany shortly after World War II. The
dependence of the incidence on dosage, i.e., injected activity per
unit body weight, and on time after treatment was determined. The
observations are equally consistent with proportionality of the
incidence of cataract to the square of dosage or with a linear
dependence beyond a threshold of 0.5 MBq/kg. The possibility of a
linear dependence without threshold was strongly rejected (P less
than 0.001). The analysis of temporal dependences yielded a
component that was correlated with the injected amount of 224Ra and
a component that was uncorrelated. The former was inferred by a
maximum likelihood analysis to increase approximately as the square
of the time after treatment. The component unrelated to the
treatment was found to increase steeply with age and to become
dominant within the collective of patients between age 50 and 60.
The relative magnitudes of the two components were such that a
fraction of 55 to 60% of the total of 58 cataracts had to be
ascribed to the dose-related incidence. Impaired vision due to
cataract was diagnosed before age 54 in 25 cases. In terms of
injected activity per unit body weight no dependence of the
sensitivity on age was found; specifically there was no indication
of a faster occurrence of the treatment-related cataracts in
patients treated at older ages.