Are children more radiosensitive?
Many publications have raised concerns regarding very small radiation doses to children with the claim that children are more radiosensitive, i.e. they are more at risk for low-dose radiation-induced cancers. Let us examine the validity of this claim.
The data commonly shown to indicate children are more radiosensitive are data such as the graph below which shows the excess cancer risk as a function of attained age, for a number of ages at exposure to the radiation. The data are from the atomic bomb survivors.
It is clear from the above graph that the excess cancer risk for someone exposed to radiation at 10 years of age is much higher than for someone who is exposed to radiation at age 50, for the same attained age of 65, for example. However, in the atomic bomb survivors, the excess cancers were observed for high radiation doses only. Since there were no excess cancers from low-dose radiation in the atomic bomb survivor data, the data in the above graph cannot be used at low doses.
Another reason stated to justify the low-dose radiation concerns in children is that they have more dividing cells which are more susceptible to DNA damage from radiation. This argument ignores the fact that there is indeed much greater amount of DNA damage occurring through natural causes even in the absence of low-dose radiation exposure. The argument also ignores the effect of the defenses triggered by the low-dose radiation exposure, of increased antioxidants, DNA repair enzymes, etc., known as adaptive protection. See the article (Feinendegen, 2013). As a result of these increased defenses, the DNA damage that would be occurring through natural causes in the subsequent period would be reduced. The net result is that there would be reduced DNA damage following low-dose radiation exposures. For example, see the graph below of the effect of radiation on mutation frequency in fruit flies.
Another effect of low-dose radiation exposures is that it activates the immune system. In a publication entitled "The DNA Damage Response Arouses the Immune System" (Gasser and Raulet, 2006), the authors explain that the normal cell, when it undergoes DNA damage, results in upregulating Rae1 and other ligands of the NKG2D receptor, which activate natural killer (NK) cells. (See figure below). The NK cells eliminate cancer cells and pre-cancerous cells, and so the result would be reduced cancers.
The increased activation of NK cells following low-dose radiation exposures is confirmed in the fgure below from (Yang, 2014).
The study of second cancers in childhood cancer survivors who underwent radiation therapy has shown that those parts of the body that received low radiation doses from the radiation treatments had a reduced rate of tumors per kg of tissue when compared to parts of body with no radiation exposure from the radiation treatments, demonstrating the occurrence of radiation hormesis in children (see Graph below). For the parts of the body exposed to high radiation doses, there was an increased risk of second cancers per kg of tissue.
Thus, there should be no concerns regarding low radiation exposures in children.
In view of the above discussion, the idea that children are more radiosensitive, that they are more at risk from low-dose radiation exposures, is incorrect. For high radiation doses, children are indeed more radiosensitive.