Radiosensitivity of Children

In contrast to radiation doses, age-dependent radiosensitivity has been treated in the current ICRP recommendations rather lightly [2]. In the 1990 recommendations of the ICRP it was reported that the total risk determined as the sum of the individual organ risks differs by a factor of about 3 for young (0–19 years) versus older (20–64 years) age groups [1]. For the development of radiation protection in the current ICRP recommendation, the average detriments for ages 18–64 years at exposure were used for workers and those for ages 0–85 years were used for the public.

After radiation exposure, children are reported to be more radiosensitive for about 30 % of tumor types when compared with adults. These types include leukemia and thyroid, skin, and brain cancer. They have the same sensitivity as adults when it comes to 25 % of tumor types such as kidney and bladder, and are less sensitive than adults when it comes to 10 % of tumor types including lung cancer.

For effects that are bound to occur after high doses, UNSCEAR [9] concluded that, as seen with carcinogenesis, there are some instances in which childhood exposure poses more risk than adult exposure (e.g., for effects in the brain, cataracts, and thyroid nodules). There are other instances where the risk appears to be about the same (e.g., neuroendocrine system and effects in the kidneys), and there are a few instances where children's tissues are more resistant (lung, immune system, marrow, and ovaries).

Effective Dose Adjusted by Age Weighting Factor for Radiation Protection

Radiation exposure means the process of being exposed to radiation or radionuclides, and the significance of exposure is determined by the resulting radiation dose. Thus, dose can be considered a quantitative expression of risk of radiation exposure. In protecting individuals from the harmful effects of radiation, it is the control of radiation doses that is important, no matter what the source.

The ICRP's system of radiological protection aims primarily to protect human health. It is to manage and control exposure to radiation so that deterministic effects are prevented and risk of stochastic effects is reduced to the extent reasonably achievable.

In view of the uncertainties surrounding the values tissue weighting factors and the estimate of detriment, currently the ICRP considers it appropriate for radiological protection purposes to use ageand sex-averaged tissue weighting factors and numerical risk estimates.

However, quantitative information on the age-dependent risk coefficients of radiation exposures can be now considered to be available. Actually, WHO [11] has calculated health risk for various age groups. To control exposure so that the risk is reduced to an extent we have to develop a measure applicable to all age groups. As described previously, age-dependent dose coefficients have been already provided by ICRP. Now, it is needed for the ICRP to prepare a new report on the age-dependent radiation risks, and then to develop a new system of radiation protection for the general public to include radiation protection scheme for children based on the agedependent radiation risks. I think there are two approaches: development of new radiological protection criteria for children, and development of a new effective dose adjusted by age weighting factors.

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