Concepts of association between cancer and ionising radiation: accounting for specific biological mechanisms

The probability that an observed cancer was caused by radiation exposure is usually estimated using cancer rates and risk models from radioepidemiological cohorts and is called assigned share (AS). This definition implicitly assumes that an ongoing carcinogenic process is unaffected by the studied radiation exposure. However, there is strong evidence that radiation can also accelerate an existing clonal development towards cancer. In this work, we define different association measures that an observed cancer was newly induced, accelerated, or retarded. The measures were quantified exemplarily by Monte Carlo simulations that track the development of individual cells. Three biologically based two-stage clonal expansion (TSCE) models were applied. In the first model, radiation initiates cancer development, while in the other two, radiation has a promoting effect, i.e. radiation accelerates the clonal expansion of pre-cancerous cells. The parameters of the TSCE models were derived from breast cancer data from the atomic bomb survivors of Hiroshima and Nagasaki. For exposure at age 30, all three models resulted in similar estimates of AS at age 60. For the initiation model, estimates of association were nearly identical to AS. However, for the promotion models, the cancerous clonal development was frequently accelerated towards younger ages, resulting in associations substantially higher than AS. This work shows that the association between a given cancer and exposure in an affected person depends on the underlying biological mechanism and can be substantially larger than the AS derived from classic radioepidemiology.

     

Risk bases can complement dose bases for implementing and optimising a radiological protection strategy in urgent and transition emergency phases

Radiation and Environmental Biophysics - Current radiological emergency response recommendations have been provided by the International Commission on Radiological Protection and adopted by the...     

Water content and size of spore components determined by laser diffractometry

For the first time laser diffractometry was used to obtain the refractive index distribution within individual cells in an aqueous environment, allowing accurate determination of their compartmental water content. For bacterial spores the results demonstrated the existence of a dehydrated protoplast surrounded by a less dehydrated integument, thus accounting for the extreme heat resistance of the spores. In contrast, the presence of a dry wall surrounding a water-rich protoplast was shown in fungal spores.     

The influence of the cortex on protoplast dehydration in bacterial spores studied with light scattering

Individual, dormant spores ofBacillus sphaericus were studied with laser diffractometry. Correlation coefficients were obtained for the water content and radius of the protoplast and the water content and thickness of the integument of the spores. The coefficients showed that the states of the protoplast and the integument were interrelated. The water contents of the protoplast and the integument were positively correlated (=0.73), and spores with thinner integuments had more dehydrated protoplasts. The coefficients were compared with qualitative predictions based on current models of the mechanism responsible for protoplast dehydration. The results did not support models involving an expansion of the cortex as the cause of the dehydration, but were consistent with cortex contraction and the model in which the cortex maintained rather than produced the dehydrated state of the protoplast.