Safety_Series_025_1968 - gnssn - International Atomic Energy ...

This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.3.2. C hronic and d elayed radiation e ffe c ts1.3. 2.1. G eneral c h a ra cte risticsL ate radiation e ffe cts a re g en era lly con sid ered as th ose thatappear many months or years after irradiation. They may be roughlydivided into two ca te g o rie s: effects which are caused by ch ron icirradiation with sm all d ose rate and effects follow ing acute ir r a d i­ation after a certain tim e -la p s e .It is usually d ifficu lt to distinguish betw een a late effect and ad isease induced by other causes, som e of which may be entirely unknown.When populations irradiated fo r m ed ica l reason s are con ­sidered, it should be borne in mind that the treated disease itself maysim ulate a radiation effect.Late effects may be caused by loca l irradiation of tissu es or byw h ole-b od y irra d ia tio n after a certa in p e rio d o f tim e . T he m ostim portan t late e ffe ct is the induction o f tu m ou rs.1. 3. 2. 2. L ate e ffe cts a fter lo c a l irra d ia tio nOne ch a ra cte ristic late effect is the d e cre a se in life -s p a n . Itis known that p artial-bod y irradiation d ecrea ses the life-sp a n muchle s s than w hole-body irradiation (see T able V).Induction o f len s op a city (see a ls o s e ctio n 1. 3. 1.8) throughcataract form ation m ay be the outcom e o f l o c a l irradiation. C lin icallysignificant cataracts in man may be produced by an X -r a y doseof 600 - 1000 rads. The p ro g re ss of the developm ent of the lensop a city is dependent on the s iz e o f the d o se . The fra ction a tion ofthe d o se d e c r e a s e s the in cid en ce o f ca ta ra ct and a lso reta rd s itson set. G en erally the lens op acity p r o g r e s s e s slow ly and in som eca se s a slight r e c o v e r y has been o b serv e d .Among im portant late effects are in ju ries to the skin: derm atitis,atrophy, epilation, hyperkeratosis, vascular scle ro s is, telangiectasia,etc. T hese changes m ay p ro g re ss in a rythm ic way changing fromsta g es o f r e la tiv e a m e lio ra tio n to d e te r io r a tio n and v ic e v e r s a .N ep h rosclerosis and related hypertension m ay appear as a lateeffect after ov er-ex p osu re of the kidney region. Sim ilarly, intensiveirradiation of the lungs may cause p rogressiv e fib rosis with a rteriosc le r o tic changes. It m ay be said that degen erative changes in theblood v essels together with destruction of parenchym atous cells arech a racteristic of the late effects of irradiation .41