Radiation can damage DNA through direct interaction or via free radicals produced by ionizing water molecules. Single strand breaks are readily repaired by cells while double strand breaks can lead to cell death, mutation, or cancer. Chromosomal aberrations like rings, dicentrics, and anaphase bridges occur when broken DNA strands reattach incorrectly. Radiation exposure increases risks of genetic effects like mutations, chromosomal abnormalities, and heritable diseases. The testes and ovaries are highly radiosensitive tissues. While large radiation doses can harm pregnancies, effects depend on gestational timing, with earlier exposures posing greater risks.

1. Biological effects of radiation
by
Daniel.j
Khorfakkan Hospital

2. Xray Interactions

3. Energy in tissues
Energy from free radicals and ionisation remain
as 1-Spur. 2-Blobs. 3- Short tracks.
Spur :released by rays.It consists 3 ion pairs and
energy equal to 100eV.Diameter of 4nm.
Blobs and Short tracks: are released by alpha
particles and neutrons.It consists of 12 ion pairs.
Diameter of 7nm.

4. Blobs and Short tracks

5. Biological effects of Radiation
Ionisation leads to a series of
radiochemical or biochemical
reactions causing damage to
biomolecules such as proteins
and DNA by breaking vital
chemical bonds and ultimately
causing biological damage to
the critical target which is
DNA.

6. Biological Effects
The principal target - DNA
• Direct action: where the radiation interacts
directly with the DNA eg:neutrons or
alpha.
• Indirect action: where radiation interacts
with atoms or molecules.

7. Indirect reaction
eg:Free radicals from water.
H2O  H2O+
+ e¯.
This H2O+
is called ion radical
H2O+
+ H2O  H3O+
+ OH
(OH) Hydroxyl radical is highly reactive
causing damage to DNA.

12. Strand Break

13. Basic structure of DNA
Nucleic acid is composed of two
strands,linked together by hydrogen
bonds between the bases.
(adenine,thymine,guanine,and cytosine).
The genetic information is contained in the
sequence of bases.
Sugar and phosphate form the frame work
to hold the bases.

14. Cell Division

15. Strand Breaks
Single strand break are readily repaired.
Double strand break result in cell killing,
mutation and carcinogenesis.
Strand breaks result in mutation.
Break is followed by repair.

16. Chromosomal aberration
• Strand breaks are produced.
• Broken ends are sticky.
• These broken ends rejoin.
• An orginal configuration(restitute)
• Give rise to aberration.
• Reassort and rejoin.

17. Chromosomal aberration
Three lethal aberration
• Ring
• Dicentric
• Anaphase bridge

18. Ring
A break occurs in the arm of same
chromosome.
Sticky ends unite to form a ring and an
acentric fragment.

19. Ring chromosome

20. Dicentric
It happens in early phase of cell division.
Chromatids break in, two separate
chromosomes . sticky ends then join.
Resulting in a single chromosome with two
centromere.

21. Dicentric Chromosome

22. Anaphase Bridge
Anaphase Bridge-This happens in late
phase of cell division
Break occurs resulting in an incorrect union
of the same chromosome resulting in a
sister union.
This is the most lethal of chromosomal
aberration.

23. Anaphase Bridge

24. Non lethal chromosomal change
Symmetric translocation :-Break occurs
within the same chromosome,and the
broken ends are exchanged.
Small delection :- Break occurs resulting in
loss of genetic information.

25. Symmetric translocation

26. GENE
Genes:It’s the sequence of nucleotide bases
along the DNA molecule
Genes determine human character,
personality and talents.
Gene mutation:-Change in structure of DNA
involving base, sequence or both (change in
the insertion of these bases cause mutation).
Eg:- A single base loss resulting in sickle cell
disease.

27. Chromosome
23 pairs = 46 23 from eggs
23 from spermatocyte
Chromosome 23 pairs 1 from father
1 from mother
(Out of 23,22 pairs somatic cells&1pair
germ cell

28. Chromosome
Somatic cells(organs) and germ cells
(involved in reproduction).
Damage in most often repaired.
Misrepair (incorrect repair) leads to DNA
instability or genomic instability.
Genomic instability of somatic cells cause
cancer.
Small doses of radiation can cause DNA
damage in germ cells .

29. Harmful Effects
Stochastic effects:is an effect in which
probability of occurrence with increased
absorbed dose
Deterministic effects :-is a effect which
occur after a threshold dose.
Dominant gene show their effect if one of
the pair is dominant .
Recessive gene if both of the pair is altered
or deffective.

30. Heritable effects of radiation
• Chromosomal aberration - Down’s
syndrome, embryonic deaths.
• Sex linked - Colour blindness, haemophilia.
• Gene mutation single dominant -
Polydactly,retino blastoma
• Recessive - Sickle cell ,Cystic fibosis, Tay
sachs disease.
• Frequent but mild mutation - Low
probability of survival from eggs to adult.

31. Dosimetry in radiation
Exposure:-It’s a quantity of ionisation
produced per kg of air expressed in
Roentgens(R).
1R = 2.58c/kg air.
1Kerma is the kinetic energy absorbed per
unit mass.
1Kerma = 114R
1Kerma=1Gray(100rads)

32. Dosimetry in Radiation
Gray-it is the unit of absorbed dose expressed as j/kg.
1Gy=1000mGy(100rads)
Dose equalent-it is the product of absorbed dose and
quality factor.
H = DQ
Expressed in Sieverts(j/kg).
1Sievert=1000mSV(100rems)
Quality factor
X&Gamma and electrons = 1
Neutrons = 5
Heavy particles = 20
1Gy=1Sv(1000mSv =1000mGy)

33. Effective dose equivalent
The dose to different organs vary.It is the
sum of dose equivalent for different
tissue given by a tissue weighing factor
Wt (which represents the risk to
different tissues).
HE =∑ Wt Ht
1 Gy = 1000 mGy
or
1 Sv = 1000 m Sv

34. Operational limits:-
Lens of eye – 150 m Sv
Red bone marrow breast, lungs,gonad =
500m Sv
Effective dose equivalent = 5mSv or
should not exceed the value of his age.

35. Effects in pregnancy
Pregnant mother:-
Large doses (2.5Gy) delivered before 2-3 wks of
gestations are not likely to produce severe
abnormalities.
4-11wks of gestation severe abnormalties of many
organs.
11-16 wks of gestation – produce eye,
skeletal,genetal abnormalities,stunted
growth,microcephaly,mental retardation.
16-20 wks – mild degree of microcephaly, mental
retardation,stunted growths.
After 30 wks – not likely to produce structural
abnormalities but functional abnormalities.

36. Reproductive organs
Male:-2-3 Gy – maturation of spermatocytes
is stopped.
4-6 Gy – spermatids damaged
Above 6 Gy – no sperm production
Female 6 Gy – amenorrhea in prepubertal
girls.
10-20Gy – amenorrhea in 30% women (30-
35yrs)
80% women 35-40yrs

37. Radiosensitivity
Radiosensitivity – The relative
vulnerability of cells to damage by
ionising radiations.Highly sensitive cells
are readily damaged by fairly low doses.
High sensitivity :-
Epithelium of skin,
Epithelial lining of alimentary canal.
Haemopoietic tissue.
Reproductive cells of ovary and testis.

38. Radiosensitivity
Intermediate sensitivity
:-Liver,kindney,lungs and many
glands.(eg:thyroid)
Low sensitivity:-
muscle,bone,connective,nerve tissue.
Radiation sickness – due to treatment
or accidental exposure.
Clinical features
:-nausea,headache,tiredness,weakne
ss.

39. Radiation Syndrome
Prodromal syndrome – At doses
greater than 100Gy , reactions
within 15mts reaches the maximum
in 30 mts.death occurs 24-48 hrs.
Cerebro vascular sydrome:-At
doses of 100Gy death within 24-48
hrs
Sign and symptoms :- disorientation
siezures,diarrhea,coma and deaths.

40. Radiation Syndrome
Gastro intestinal syndrome:-At dose more
than 10Gy
Nausea,vomiting,prolonged diarrhea
dehydration,loss of weight,deaths occur(3-10
days)
Haemopoetic syndrome :-Dose of 3-8 Gy-
production of Rbc Wbc and platelets
diminished.
Signs & symptoms:-
chills,fatigue,heamorrhage in skin, ulcers in
mouth,epilation ,hemorrhage due to
depression of platelet ,infection and fever
from depression of immune mechanism finally
leading to death.

41. CONCLUSION
• Most mutation induced by radiation are harmful.
• Any dose of radiation,however small has some
genetic risk.
• Cell killing may be expressed in hours to
days,cancer manifestation may take 40
years,mutation may not be expressed for many
generation.
• In the event of an accidental heavy exposure
,deleterious genetic consequences can be avoided
if conception is delayed for atleast 6 months (M/F).
• Retrospectively it is impossible to attribute a small
dose of radiation to a,given anomaly,but radiation
can increase the probability of an anomaly.

42. Thank you