2. BIOLOGICAL EFFECTS OF RADIATION
• Radiation can cause cause biological damages
on either by direct & indirect action
• If radiation falls on human body, it produces
moving electrons.
• These electrons causes ionization , excitation
resulting in chemical and molecular changes.
• Radiation can also produce free radicals,
which are unpaired electrons that are
chemically reactive.
3. • Ex: radiation can interact with water molecule
and produce hydroxyl (OH) and hydrogen(H)
radicals.
• These free radicals interact with DNA,RNA or
PROTEIN molecule and cause damage tissue.
• Chromosomal breaks and aberrations are
examples of biological damage caused by
radiation.
• Scoring of human lymphocytes is used as
biological dosimeter
4.
5. • Radiation induce structural changes in a DNA
molecule
• 1) hydrogen bond break
• 2)molecular breakage
• 3)inter and intramolecular cross linking
6. • Hydrogen bond break disturbs the base pairs
such as adenine-thymine resulting in genetic
changes.
• Molecular breakage may involve single strand
break and double strand breaks.
• Single strand breaks are mostly repairable.
• Double strand breaks are irreparable and
cause loss of base or change of base called
mutation, leading to carcinogenesis
7. • High dose of radiation can cause
• 1) cell death (deterministic effect)
• 2) cellular transformation (stochastic effect)
• Lymphoid tissue and rapidly proliferating tissues
(spermatids & bone marrow stem cells) are
relatively radiosensitive
• Nerve cells are least radiosensitive
8. • An acute dose delivered in a short time is
more harmful than a chronic dose delivered
over a period of time
• The radiation effects which manifest soon
after radiation are called early effects
• Those effects that manifest after a short
period of time are called late effects.
9. • The harmful effects of radiation are
• 1) deterministic effects
• 2) stochastic effects
10. DETERMINISTIC EFFECTS
• In this effect “ severity increases with
increasing absorbed dose”
• These effects appear at high doses > 0.5 Gy
and generally result from cell death
• These effects are characterized by threshold
dose, below which the effect does not occur
• These include skin erythema, epilation, organ
atrophy, fibrosis, cataract induction, blood
changes and reduction in sperm count.
11.
12. Stochastic effect
• In this effect,” the probability of occurrence
increases with increasing absorbed dose rather
than its severity”
• Classified in to somatic and genetic effects
• Severity of stochastic effect is independent of
radiation dose
• It has no threshold dose, may occur even at low
doses
• Radiation induced cancer and hereditary effects
come under this category
13.
14. ACUTE RADIATION SYNDROME
• Whole body radiation exposures involving
high level radiations delivered in shorter
interval can cause acute radiation syndromes
• It includes
• 1) haemotopoietic syndrome
• 2) gastrointestinal syndrome
• 3) cerebrovascular syndrome
15. LAW OF RADIOLOGY/ LAW OF
TRIGONIE AND TRIBONDEAU
Tells about radiosensitive and radioresistant tissues
Radiosensitive tissues: tissues which have
maximum number of undifferentiated cells/cells
in active mitosis
ex bone marrow ( acute haematological syndrome)
GI mucosal cells (acute GIT syndrome)
Acute CNS/CVS is the last syndrome which occurs
because CNS cells are radioresistant
16. • clinical stages of acute radiation syndrome
• Stage1/prodromal stage-nausea,vomiting,diarrhoea.
few minutes to hours
• Stage2/latent stage: few hours to days
• Stage3/manifest illness stage: few days to weeks
• Stage4/recovery/death stage: few weeks to years
17. • ACUTE HAEMATOLOGICAL SYNDROME
• Threshold dose: 1-2 Gy
• Results in pancytopenia
• Recurrent infections and recurrent
haemorrhages are the cause of death in these
pts
18. • ACUTE GIT SYNDROME
• Threshold dose: 6-10 Gy
• Radiation enteritis (mucosal layer is shed off)
usually presents as diarrhoea
• Other symptoms: malaise, severe diarrhoea,
electrolyte imbalance
19. • ACUTE CNS/CVS SYNDROME
• Threshold dose: 20 GY
• Death usually occurs due to circulatory
collapse or raised ICT
20. • Doses > 100 Gy may cause death in 24-48 hrs-
cerebrovascular syndrome.
• Dose 5-12 Gy may cause death in days -
gastrointestinal syndrome.
• Dose 2.5-5 Gy may cause death in weeks to
months -haematopoietic syndrome.
• The dose that causes 50% death over a specified
time (60 days) is called lethal dose and is
expressed in LD50/60, which is about 4 Gy for
humans
21. ALARA PRINCIPLE
• It is the principle which deals with radiation
safety
• It is followed when ever there is requirement
of radiation exposure to the pt i.e, as low as
reasonably achievable
• And not very low because image quality would
be compromised which results in misdiagnosis
22. • In reproductive age group, All x-ray based
investigations should be done in the first 10
days of the menstrual cycle
• Ideal time for HSG: 6th to 10th day
Injection of contrast is avoided in the first 5-6
days to prevent the risk of infections
23. • CLASSIFICATION OF RADIATION EXPOSURE IN VARIOUS
MODALITIES
• 1.Green zone/safe zone/spot radiographs
• Pt exposed to radiation once(chest x ray) or twice(x ray
wrist)
• 2.yellow zone/warning zone/diagnostic procedures
• pt exposed to radiation multiple times(IVU,MCUG)
• 3.red zone/danger modalities
• Radiation exposure very high (CT
HEAD/THORAX/ABDOMEN), PET scan, bone scan
24. ICRP/ICRU GUIDE LINES
• ICRP: international commission on radiology
protection
• ICRU: internation commission on radiation units
• Public exposure: effective dose 1msv/year
• annual equivalent dose to lens of eye 15 msv
• Annual euivalent dose to skin 50 msv
• For pregnant and radiation workers- should not
to exceed 1msv
25. • Occupation exposure
• Effective dose over all 20msv/yr..(< 100 msv in
5 yrs)
• Annual equivalent dose to lens of eye 150 msv
• Annual equivalent dose to skin 500 msv
26. RADIATION RISK
• When exposed to radiation, the expected risk
includes
• 1) somatic risk
• 2) genetic risk
• 3) fetal risk
27. Somatic risk
• The radiation effects, produced in an
individual during his life time are called
somatic effect
• Cancer induction is the largest risk
• Bone marrow, gastrointestinal mucosa, breast
tissue and lymphatic tissue are most
susceptible to radiation induced malignancy
• Cancer risks are generally higher for children
than for adults
28. Genetic risk
• The radiation effects produced in the
successive generation of the exposed
individual are called genetic effects
• These effects are the result of radiation
exposure to the gonads
• There is no epidemiological evidence of
genetic effect in humans
• The current ICRP risk estimate for hereditary
effects is 0.1% per Sv
29. Fetal risk/pregnancy
• The effects of radiation on embryo and fetus are
• 1) lethal effects
• 2)malformations
• 3)growth disturbances
• The developmental period in utero has three
stages namely 1)preimplantation
• 2)orgnogenesis
• 3)fetal period
30. • Preimplantation is the most sensitive stage,
which causes lethal effects.
• The fetal risk depends on the gestation period of
the pregnant women
• Mothers exposed to diagnostic x-rays in the third
trimester, resulted in excess childhood leukemia
• Diagnostic x-rays can increase the risk of
chidhood cancer by 40%
• To avoid radiation induced congenital anomalies,
an abortion may be advised only when dose
exceed 100 mGy
31. RADIATION PROTECTION
• The aim of radiation protection is to prevent
deterministic effects and limit the probability
of stochastic effects
• These could be achieved by
• 1) setting limits well below threshold dose
• 2)limiting exposures as low as reasonably
achievable (ALARA)
32. • The whole radiation protection summarized as
• 1) justification of practice: no radiation exposures
shall be adopted unless it produces a net positive
benefit
• 2)optimization: every effort shall be taken to
reduce the dose as low as reasonably achievable
• 3)dose limits:the effective doses to the
individuals shall not exceed the limits
recommended by the commission
33. • Pregnant radiation workers are monitored by
a dosimeter worn on the abdomen under the
lead apron
• A measured dose of 2 mSv to the surface of
the abdomen is normally considered
equivalent to 1 mSv to the fetus
• The dose limits for members of the public are
generally 10 times lower than those for
occupation exposure
34. • The three principal methods by which
radiation exposures to persons can be minized
are
• 1) time
• 2) distance
• 3) shielding
35. Time
• The total dose received is directly proportional
to the total time spent in handling the
radiation source
• Techniques to minimize time in a radiation
field should be recognized or practiced.
• Nuclear medicine procedure produces lower
exposure rate for extended period of time
36. Distance
• Radiation intensity (exposure rate) from a
point source decreases with distance due to
divergence of a beam
• Exposure rate from a point source of radiation
is inversely proportional to the square of the
distance.( inverse square law)
• If the exposure rate is X1 at distance d1, then
the exposure rate at another distance d2 is
given by X2 = X1(d1/d2)2
37. • In diagnostic radiology at 1m from a patient,
the scattered radiation is about 0.1-0.15% of
the intensity of primary beam
• Personnel should be atleast 2m from the x ray
tube and behind shielded barrier or out of
room
• Imaging rooms should be designed to
maximize the distance between the source
and control console
38. shielding
• The material that attenuates the radiation
exponentially is called shield
• The shield will reduce the exposure to patients,
staff and public
• Larger the shielding thickness, lesser the
radiation exposure
• The thickness of the shielding material that
reduces the intensity to half is called half value
thickness(HVT) and is given by relation
HVT= 0.693/mu
39. • Optimal shielding is required to bring down
the radiation level below he permissable limit.
• Brick, concrete are used as shielding material
for construction of x-ray room barriers
• Lead is used as protective material in lead
apron, thyroid shield and gonad shield
40. • The calculation of barrier shielding require the
understanding of five factors
1)Workload
2)Use factor
3)Occupancy factor
4)Distance
5)Radiation exposure level
41. • GOOD WORK PRACTICES IN DIAGNOSTIC
RADIOLOGY
• 1)X-RAY EXAMINATION
• X-ray examination should be prescribed only
after critical evaluation of patients condition
in order to avoid unnecessary exposures
• No fluoroscopic examinations should be
conducted , if the required information can be
obtained by radiography
42. • 2) QUALITY ASSURANCE
• Every new x-ray unit shall be subjected to to
quality assurance tests before patient use
• Only qualified x-ray tecnologists will be
allowed to handle x-ray equipment
43. • 3) EQUIPMENT OPERATION
• Personnel monitoring devices shall be used by
all radiation workers while on duty
• Before making an exposure, the doors of the
x-ray room must be closed
• While performing portable examinations, the
operator should stand atleast 2m away from
the pt
44. 4)PROTECTIVE SHIELD
- All radiation workers must wear lead apron of
0.5 mm thickness, which reduces radiation
exposure by a factor of 10
-use of leaded glasses, lead gloves must be
encoraged in fluoroscopy type of work
-thyroid shield, gonad shield,eye shields
should be used to protect the patient during
radiography
45. • 5)FIELD AREA
• Minimal field size to cover the pt volume
shoulf be used
• Field size reduction reduces the scatter
thereby reducing the dose to adjacent organs
• The scatter incident on the detector also
decreases, resulting in improved image
contrast
46. • 6)SOURCE TO OBJECT DISTANCE
• Higher the source to object distance(SOD) and
source to image distance(SID),lesser the
patient dose
• Increase of SOD/SID, reduces beam
divergence , in turn reduces the volume of
patients irradiation
47. • In radiography and fluoroscopy with
stationary X-ray equipment, the SOD should
be not less than 45cm
• Chest radiography should be performed with a
SID of atleast 120cm
• in flouroscopy, the minimum distance
between source and the patient must be not
less than 30cm
48. • 7)OCCUPANCY IN THE ROOM
• Only persons whose presence is necessary
should be in the imaging room during
exposure
• All such persons must be protected with lead
aprons/shields
• The x-ray room should be kept closed during
radiation exposure
49. • 8) ASSISTANCE TO PATIENTS
• Holding of children or infirm patients for X-ray
examination shall be done only by adult
relative of the patient
• Hospital personnel should not hold patients
during imaging procedure
50. • 9)PREGNANT WOMEN
• radiological examination of the lower abdomen and pelvis
of a pregnant women must be conducted only when
considered absolutely essential
• 10)LOG BOOK
• Each X-ray equipment must have a separate log book,
which provides information about the equipment
manufacturer, model, serial number, date of purchase
• 11)RECORDS
• Records of all radiological examination must be maintained
51. SUMMARY
• BIOLOGICAL EFFECTS OF RADIATION
• Radiation induce structural changes in DNA molecule 1)
hydrogen bond break, 2) molecular breakage, 3) inter
and intramolecular cross linking
• The harmful effects of radiation 1)deterministic effects
& 2)stochastic effects
• Acute radiation syndrome includes 1)haematopoietic
syndrome, 2)gastrointestinal syndrome,
3)cerebrovascular syndrome
52. • Radiation risk- 1)somatic risk 2)genetic risk 3)fetal risk
• RADIATION PROTECTION
• Whole radiation protection summarized as
1)justification of practice 2)optimization 3)dose limits
• The three principal methods by which radiation
exposure can be minimized 1)time 2)distance
3)shielding
