Safety_Series_025_1968 - gnssn - International Atomic Energy ...

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This publication is no longer validPlease see http://www.ns-iaea.org/standards/1. 3. 2. 3. Late effects after whole-body irradiationUnder continuous w h ole-bod y irradiation at d ose rates as highas 0. 5 ra d /d , no d ifferen ce in life-sp a n between irradiated and control animals was observed (F ig. 10).D elayed in ju ries have been ob served in b lo o d -fo rm in g organ s.They m anifest th em selves in the form of aplastic anaemia orpancytopenia. E xact rela tion sh ip s betw een d ose and e ffe ct a relack ing. Am ong the su rv iv o rs at N agasaki and H iroshim a delayedin ju ries (with the exception of leukaem ia) are generally ra re . Someirradiated p erson s died from cach exy connected with d istu rban cesin the haem atopoietic apparatus.1.3. 2. 4. Genetic effectsIrradiation of the germ tissu es m ay cause mutations which appearin later generations. The follow ing features are ch aracteristicof mutations:(a) Mutations having once occu rred are permanent. The mutantgenes may be restored only by a re v e rse mutation and this has onlya slight probability o f o ccu rrin g . In the p rocess of selection som eof the mutant genes m ay be elim inated.•(b) The great m a jority of ob serv ed mutations are d e le te rio u s.(c) It has not thus fa r been p roved w hether a th resh old d o seex ists fo r m utations. T his m eans that every ion izin g radiationlocated in a germ cell should be assum ed to have a sm all statisticalprobability of causing a mutation.(d) Sm all d oses m ay be cum ulative and the end resu lt m ay notappear until many generations la ter.(e) The gen etic d o se req u ired to double the m utation ra te inman is of the ord er of 10 to 100 rads. It cannot be less than 3 radssin ce this level is attained in a human generation of 30 yea rs as theresu lt of natural radiation. However, recent work may indicate thatat low d ose rates the d ose requ ired to double the m u tation -rate inman m ay be la rg e r than indicated h ere.A whole range of ch a ra cte ristics m ay be influenced by gen eticdam age, including variou s m orp h olog ica l and b io m e trica l ch a ra cte r is tic s (life-sp a n , weight at birth, in tellig en ce, fe rtility , lethaleffects, etc.). Owing to the uncertainty of som e of the genetic m echanism s in volved, it is safest to assum e that approxim ately 4% ofchildren born are at present burdened with hereditary disturbances.42
This publication is no longer validPlease see http://www.ns-iaea.org/standards/An in crea se in the level of radiation could lead to an in crea se in thisgenetic load.1.3. 2. 5. Radiation carcin ogen esisThe data on radiation ca rcin og en esis was recen tly surveyed bythe UN S cien tific C om m ittee on the effects of atom ic radiation andpublished in its rep ort issu ed -in 1964.One of the first significant late effects o f irradiation was the d evelopm ent of skin ca n ce rs am ong ra d io lo g ists. It w as establish edlater on that there is a causal link between irradiation and incidenceof leukaem ia.It was not easy to show a relationship between radiation exposureand leu k aem ia. C onsistent data a re available m ainly fo r the s u r v iv ors of the explosions at H iroshim a and Nagasaki. The su rvivorshave been divided into groups a ccord in g to the estim ated d ose theyr e c e iv e d . T he estim a tes of the d o ses are a lm ost ce rta in ly not ine r r o r by a fa ctor g rea ter than two or th ree. An approxim ate p r o p ortion a lity o f the avera ge y e a rly in cid en ce o f rad ia tion -in d u cedleukaem ia fo r the p eriod from 1950 to 1958 was found in the rangefrom about 100 to 900 ra d s. The p robable rate o f in crea se o f in c idence with d ose is between 1 and 2 ca ses p er year p er rad perm illion exposed individuals. This estim ate is also valid in the rangebetween 300 and 1500 rads for induction of leukaemia among patientsirradiated therapeutically for ankylosing spondylitis.Important are the resu lts of a su rvey of induction o f leukaem iaam ong ch ild ren irra d ia ted in u te ro . U nder ce rta in con d ition s,radiation d oses of the ord er of a few rads can induce malignantgrow th. The highest risk was with m others exposed fo r diagnosticX -r a y pelvim etry during the first three months of pregnancy.The in ciden ce o f thyroid carcin om a as a result o f irradiation o f thethyroid region for therapeutic purposes during childhood is also prop ortionalin a range of d oses between 100 and 300 rads and leads to a sim ilarrisk estim ate as in the case o f leukaem ia of the atom ic bom b su rv iv o rs.A ll these resu lts indicate the p ossib ility that ionizing radiationm ay in crea se the p robability o f induction m align ancies in man andthat in som e c a s e s , p a rticu la rly am ong young individuals, the n ec e s s a r y d ose m ay be v ery low .It should be alw ays born e in mind that many types o f tum ourso ccu rrin g in man a re, as fa r as we know, not induced by ion izin gradiation (e.g. the tum ours of g a stro -in te stin a l tra ct, o f u teru s,m am m ary tu m ou rs etc.).43
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