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Safety_Series_025_1968 - gnssn - International Atomic Energy ...

Safety_Series_025_1968 - gnssn - International Atomic Energy ...

This publication is no

This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.2 . 1 .5 . 5. Whole-body and partial-body irradiation. Lethal dosesfo r w h ole-b od y irra d ia tion (e .g . L D 50 valu es) are g en era lly m uchlo w e r than fo r p a rtia l-b o d y irra d ia tion . S u cce ssfu l radioth erapyis based on this circu m sta n ce. But there are exceptions to this rulesin ce som e org an s a re rela tiv e ly m o re sen sitiv e and re sp o n sib lefo r radiation dam age ( e .g . intestine and h a em op oietic apparatus;and therefore shielding o f bowel and bone m arrow prolongs survival).Table IV shows the effects and sign ifican ce of various radiationd oses. It can be seen that there is a con sid era ble d ifferen ce in theresu lts o f lo c a l o r w h ole-b od y e x p o su re . T h is is b eca u se duringw h ole-body exposure slight in ju ries in d ifferen t organs are integratedand the acute radiation syndrom e resu lts.F o r v e ry sm a ll d o ses o f natural radiation (c o s m ic ra y s, theradiation from radioactive substances contained in the earth 's crusto r p resen t in the human body), it is not d ifficu lt to show that theprobability of ob servable effects at the level of natural radiation isv ery low and it w ill be n ecessa ry to study an extrem ely large populationto dem onstrate any sign ifican t e ffe cts . Other fa cto rs o f thehuman environm ent com e into play and may produce sim ila r effects(ch em icals, heat etc).T A B L E IV . E F F E C T S AND SIG N IFICAN CE OF VARIOU SR A D IA T IO N DOSES IN M ANDose o f single exposure toX - or gam m a-radiation(rad)Expected e ffe ct orb io lo g ica l significanceLocal exposure3000 Tumour dose in radiotherapy3000 Skin necrosis500 - 1000 Skin erythema300 - 600 EpilationW hole-body exposure400 50°]o m ortality (y-rays)75 - 150 Blood changes and possible acute injury25 - 75 Blood changes but norm ally no severeacute injury28

This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.2.2. Factors governing the biological effects of radiationF rom the p rim ary p rocess occu rrin g after the absorption ofradiation a com plicated reaction develops which may finally em ergeas a v isib le reaction to radiation. As might be expected, this chaino f reactions can be influenced in variou s ways, p articularly in m orecom p lex org a n ism s. Am ong the agents which thus govern the finalrea ction to radiation a re p h y s ic o -c h e m ic a l con d ition s, in cludingtem p eratu re and d e g re e o f h ydration , oxygen and the v a rio u s s o -ca lled p ro te ctiv e su b sta n ces.1 .2 .2 . 1. P h y s ic o -c h e m ic a l con d ition s (tem p era tu re, d egree o fhydration)In general it may be said that a low ering of tem perature reducesthe e ffe ct o f radia tion . H ow ever, in som e c a s e s (b a cte ria ) th ereexists a certain optim um tem perature fo r the reduction of the ra d i­ation effect. A lso in the case of som e anim als it has been ascertainedthat storage at a low tem perature after irradiation retards the effectwhich appears only when the tem perature again r is e s to the norm allev el. The ultim ate radiation in ju ry rem ains the sam e.S im ila rly, it m ay be said that the level o f hydration o f theorganism , sp ores, seeds etc. influences the effect of radiation. Theeffect o f radiation is in creased under conditions of in creased hydration.This is evidently connected with the production o f radicals.1. 2. 2. 2. Role of oxygenIt has a lrea d y been m entioned that in w ater solu tion H2O2 o rra d ica l O2H are form ed in the p re se n ce o f oxygen after irradiationwith X - o r gamma rays. In densely ionizing alpha p articles the localconcentration of H2O2 may attain high valu es. It is th erefore understandablethat the p resen ce o f oxygen during irra d ia tion m ay be ofim portance although the inactivation of d esox yrib on u cleic acid o r ofbacteriophage (both in dried state) seem s to be governed by a m echanismindependent of oxygen tension.Quantitative relation sh ip s betw een ra d iosen sitiv ity and oxygeneffect have been studied by s e v e r a l authors. It w as found that therelation between radiosen sitivity and oxygen tension in a suspensiono f bacteria p roceed s a ccord in g to a sim ple relation, higher con cen ­trations o f oxygen in the m edium sen sitize b a cteria to the action of29

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