5-Biology effects of ionizing radiation 1.ppt

rad protection in diagnostic radiology

1. RADIATION PROTECTION IN
DIAGNOSTIC RADIOLOGY
BIOLOGICAL EFFECTS OF IOINIZING
RADIATION

2. CONTENTS
Basic concepts about radiobiology
Deterministic and stochastic effects
Radiosensitivity
Factors affecting radiosensitivity
Cell response to radiation
Systemic response
Whole body response: ADULTS
Effects of antenatal exposure
Delayed effects of radiation
Risks and weighting factors
Today:
Radiobiology

3. BASIC CONCEPTS
Interactionisaprobabilisticevent
(stochastic).
Transferofenergyoccursextremelyquickly:
approximately10
-17
s.Thus,radiation
protectionmust beappliedbefore
irradiation.
ThereisalwaysaDAMAGE ofthecell.A
consequencecouldbeCANCERinduction.
Thedamageisnotspecific,itissimilarto
otheretiologicagents.
Thereare“targets”ineverycell(points
whicharemoreprobablyaffectedbyionizing
radiation).Thisisthe“impacttheory”.

4. EFFECTS OF IONIZING
RADIATION
Deterministic
Existenceofdosethreshold(underthisdose,theeffectis
notobservable).
Effectseverityincreasewithdose.
Stochastic
Nothreshold.
Probabilityoftheeffectincreaseswithdose.
Severityisconsideredmaximum(equivalenttofatal
event).Nonfatalcancersareweighedwithacertainfactor
toaddthisprobabilitytothefatalone.

5. BIOLOGICAL EFFECTS OF
IONIZING RADIATION
Deterministic
E.g. Lens opacities, skin lesions, etc
Stochastic
Cancer, genetic effects.

6. ACTION MECHANISMS (I)
Directaction:important
moleculeisdamaged
(usuallyDNA).
Indirectaction:
environmentofthose
importantmoleculesis
altered.
Recoilelectronsinteractwithwater
molecules,producingfreeradicals.
From “Manual of clinical oncology”, UICC 1994

7. Although the
DNA may be
damaged within
a fraction of a
second, it may
take years or
decades before
an adverse
health effect
occurs, if it
occurs at all.
ACTION MECHANISMS (II)

8. DOSE-RESPONSE CURVE
Dose
Repairing cell
structures is
still possible
No repairing: a low dose
means a great damage
Practically all the cells
are dead
dose

9. RADIOSENSITIVITY (RS)
RS=Probabilityofacell,tissueor
organofsufferinganeffectperunitof
dose.
BergonieandTribondeau(1906):“RS
LAWS”:RSwillbegreaterifthecell:
Ishighlymitotic.
Isundifferentiated.
Hasagreatcariocineticfuture.

10. RADIOSENSITIVITY (II)
High RS Medium RS Low RS
Bone Marrow
Spleen
Thymus
Lymphatic nodes
Gonads
Eye lens
Lymphocytes
(exceptionto the RS
laws)
Skin
Mesoderm
organs (liver,
heart, lungs…)
Muscle
Bones
Nervous system

11. FACTORS AFFECTING
RADIOSENSITIVITY
Physical
LET(linearenergytransfer):RS
Doserate:RS
Chemical
IncreaseRS:OXYGEN,cytotoxicdrugs.
Decrease RS:SULFURE (cys,
cysteamine…)
Biological
Cyclestatus:
RS:G2,M
RS:S
Repairofdamage(sub-lethaldamage
mayberepairede.g.fractionateddose)G1
S
G2
M
G0
LET
LET
% survivor cells

12. BIOLOGICAL EFFECTS AT
CELLULAR LEVEL
Possible mechanisms of
cell death:
Physical death
Functional death
Death during interphase
Mitotic delay
Reproductive failure
Cellular effects of ionizing radiation are
studied bycell survival curves
% survival cells (
semi logarithmic
)
Dose
n = targets
D
q
D
0
(threshold)
(radiosensibility)

13. SYSTEMIC EFFECTS
Effectsmaybemorphologicaland/orfunctional
Factors:
WhichOrgan
HowmuchDose
Effects
Immediate(usuallyreversible):<6monthse.g.:inflammation,
bleeding.
Delayed(usuallyirreversible):>6monthse.g.:atrophy,
sclerosis,fibrosis.
Criteriaofdose
<1Gy:LOWDOSE
1-10Gy:MODERATEDOSE
>10Gy:HIGHDOSE
Regenerationmeansreplacementbytheoriginaltissuewhilerepair
meansreplacementbyconnectivetissue.

14. SKIN EFFECTS
FollowingtheRSlaws(Bergonieand
Tribondeau),themostRScellsare
thosefromthebasalstratumofthe
epidermis.
Effectsare:
Erythema:1-24hoursafterirradiationof
about3-5Gy
Alopecia:5Gyisreversible;20Gyis
irreversible.
Pigmentation:Reversible,appears8days
afterirradiation.
Dryormoistdesquamation:traduces
epidermalhypoplasia(doseabout20Gy).
Delayedeffects:teleangiectasia,fibrosis.
DERMIS
EPIDERMIS
Histologic view of the skin
Basal stratum cells, highly
mitotic, some of then with
melanin, responsible of
pigmentation.
From “Atlas de Histologia...”. J. Boya

15. SKIN INJURIES

16. SKIN INJURIES

17. EFFECTS IN EYE
Eye lensare highly RS.
Coagulation of proteins
occur with doses greater
than 2 Gy.
There are 2 basic effects:
From “Atlas de Histologia...”. J. Boya
Histologic view of eye:
EyelensishighlyRS,moreover,itis
surroundedbyhighlyRScuboidcells.
> 0.155.0
Visual
impairment
(cataract)
> 0.10.5-2.0Detectable
opacities
Sv/year for
many years
Sv single brief
exposure
Effect

18. EYE INJURIES

19. WHOLE BODY RESPONSE:
ADULT
Acute irradiation syndrome Chronic
irradiation
syndrome
Dose
Steps:
1.Prodromic
2.Latency
3.Manifestation
Lethal dose 50 / 30BONE
MARROW
GASTRO
INTESTINAL
CNS
(central nervous
system)
1-10 Gy
6-10 Gy
> 50 Gy
•Whole body clinic of a
partial-body
irradiation
•Mechanism:
Neurovegetative disorder
•Similar to a sick feeling
•Quite frequent in
fractionated radiotherapy

20. LETHAL DOSE 50 / 30
Itisanexpressionofthepercentlethal
doseasafunctionoftime.
Itmeans:“Dosewhichwouldcause
deathto50%ofthepopulationin30
days”.
Itsvalueisabout2-3Gyforhumansfor
wholebodyirradiation.

21. EFFECTS OF ANTENATAL
EXPOSURE (I)
PregnancytimesupposeRS
Itisnoteasytoestablishacause-effectrelationbecause
therearealotofteratogenicagents,effectsareunspecific.
Thereare3kindsofeffects:lethality,congenitalanomalies
andlargedelayeffects(cancerandhereditaryeffects).
Time
%
Pre-implantation Organogenesis Foetus
Lethality
Congenital anomalies

22. EFFECTS OF ANTENATAL
EXPOSURE (II)
Lethaleffectscanbeinducedbyrelativelysmalldoses
(suchas0.1Gy)beforeorimmediatelyafterimplantationof
theembryointotheuterinewall.Theymayalsobeinduced
afterhigherdosesduringallthestagesduringintra-uterine
development.
Time
%
Pre-implantation Organogenesis Foetus
Lethality
0.1 Gy

23. EFFECTS OF ANTENATAL
EXPOSURE (III)
Mental retardation:
ICRP establishes that mental retardation is an Intelligence Quotient score
< 100.
It is not discarded a threshold between 0.12-0.2 Gy.
It occurs during the most RS period: 8-25 week of pregnancy.
Risks of antenatal exposure related to mental retardation are:
Severe mental
retardation with a
Risk factor of
0.1/Sv
Severemental
retardation with a
Risk factor of
0.4/Sv
15-25 week8-15 week

24. DELAYED EFFECTS OF
RADIATION
Classification:
SOMATIC:theyaffectthehealthofthe
irradiatedperson.Theyaremainly
differentkindsofcancer(leukemiaisthe
mostcommon,withadelayperiodof2-5
years,butalsocolon,lung,stomach
cancer…)
GENETIC:theyaffectthehealthofthe
offspringoftheirradiatedperson.They
aremutationsthatcausemalformationof
anykind(suchasmongolism)

25. TISSUE RISK FACTOR (I)
RISKFACTOR:Thequotientbetweentheprobability
increaseofastochasticeffectandthereceiveddose.
ItismeasuredinSv
-1
ormSv
-1
.
Dose
dose
probability
Risk factor=
probability
dose

26. TISSUE RISK FACTOR (II)
EXAMPLE:Ariskfactorof0.005Sv
-1
forbonemarrow(lifetime
mortalityinapopulationofallagesfromspecificfatalcancer
afterexposuretolowdoses)meansthatif1,000people
receive1Svinthebonemarrow,5willdieduetothecancer
inducedbyradiation.
Dose
dose
probability
Risk factor=
probability
dose

27. EFFECTIVE DOSE
H
wb= w
T· H
T
Effective dose Weighting factor
(depending on the
RS of a tissue “T”)
Equivalent
dose in a
tissue “T”

28. TISSUE WEIGHTING
FACTORS: w
T
0.05Remainder
0.01Bone surface
0.01Skin
0.05Thyroid
0.05Oesophagus
0.05Liver
0.05Breast
0.05Bladder
0.12Stomach
0.12Lung
0.12Colon
0.12Bone marrow (red)
0.20Gonads
w
TTISSUE OR ORGAN

29. REFERENCES
1990 Recommendations of the ICRP. ICRP
Publication 60. Pergamon Press 1991.
Radiological protection of the worker in medicine
and dentistry. ICRP Publication 57. Pergamon Press
1989.
Avoidance of radiation injuries from interventional
procedures. ICRP draft 2000.
Manual of clinical oncology 6
th
edition. UICC.
Springer-Verlag. 1994
Atlas de Histologia y organografia microscopica. J.
Boya. Panameriacana. 1998.