Radiobiology > Stochastic Effects > No-Threshold Models of Risk (cont.)

No-Threshold Models of Risk (cont.)

It is important to note that risks of developing non-leukemic cancer are not uniform throughout an acutely exposed population; significant factors include sex, age at time of exposure, and attained age. 

  • Children are particularly vulnerable to developing thyroid neoplasms
  • Women younger than 15 years at time of exposure have significantly increased risk of developing breast cancers.

Nevertheless, considering the conglomerate of Japanese survivor data as a linear function of dose, excess cancer risk is estimated to be 8% per Sievert. 

The IRCP halves the excess cancer risk relationship to 4% per Sv for purposes of estimating risk in chronic exposure to lower doses (as expected in most workplace settings). 

This adjustment (decrease by factor of 2) for low dose exposure is considered a Dose and Dose Rate Effectiveness Factor (DDREF).

Decaying Ferris wheel in the abandoned town of Pripyat, about 4 km from Chernobyl.


The accident at Chernobyl produced at least two biologically important radioisotopes: Cesium-137 (half-life ~30 years) and Iodine-131 (half-life ~8 days).  Recall the increased incidence of radiation-induced thyroid cancer among exposed children. (Image credit:

© Copyright Rector and Visitors of the University of Virginia 2021