Radiobiology > Stochastic Effects > Heritable Effects (cont.)


Heritable Effects, continued

Jargon used for discussing mutatagenesis:

Doubling Dose. 

  • The dose of radiation, if given uniformally to an entire population, needed to double the spontaneous mutation rate for that population. 
  • For humans, this is currently estimated to be 1 to 2 Sv as extrapolated from mice experiments and from non-significant trends in Hiroshima/Nagasaki survivor data.
  • 1/ (Doubling Dose) =  the Relative Mutation Risk.  Such a fraction gives a general sense of the power any given dose has to affect the mutation rate.

Genetically Significant Dose (GSD). 

  • The gonadal dose equivalent received by persons of reproductive potential also taking into account the expected number of children for that population. 
  • The 1991 estimated GSD in the United States is approximately 0.3 mSv from 'man-made" radiation (medical and dental X-rays, radiopharmaceuticals, commercial nuclear power, miscellaneous occupational exposure, weapons-testing fallout, consumer products, air travel).

Neither the Doubling Dose nor the GSD are thresholds - as with carcinogenesis (discussed in next section) non-threshold linear or linear-quadratic models are used for risk estimation of stochastic processes. While radiation is apparently a very weak mutagen at fractionated low dose exposures, no dose is considered free of risk.

Any genetic disorder that can result from spontaneous, de novo mutation may also be induced from radiation exposure - from chromosomal aberration to point mutation of a single gene.  Even low dose, low-LET radiation exposure is considered to carry increased risk.