In November 1895, Wilhelm Roentgen discovered X-rays. Within few months of Roentgen’s discovery, eye complaints and severe progressive dermatitis were reported. In 1896, one of Edison’s assistants Clarence E Dally, involved in the production of X-ray tubes, who had been using his own hand to test their output, developed ulcerating carcinoma of his repeatedly exposed left hand. Delayed effects of radiation began to be documented only 20 years after their initial discovery, through individual case reports. In 1927, Germline mutation as a delayed effect of ionizing radiation was documented by Muller which won him the Nobel Prize. In 1928, Murphy reported 14 cases of microcephaly and mental retardation in children of mothers who had received pelvic radiotherapy early in pregnancy. In 1929, Murphy and Goldstein documented 16 more patients with similar defects of microcephaly and mental retardation among children whose mothers had received pelvic radiotherapy early in pregnancy. In 1940s and 1950s, it was a common practice to treat ankylosing spondylitis patients with radiation. It was a permanent cure and remained the treatment of choice for approximately 2 years, until it was discovered that some of the patients who had been cured by radiation were dying from leukemia. In 1942, Dunlap reported radiation induced leukemia in radiologists and other radiation workers. In 1947, the Atom Bomb Casualty Commission (ABCC) was established, which subsequently reported the incidence of genetic effects, mutations, cataracts, leukemias and other malignancies in the population exposed in Hiroshima and Nagasaki atomic bomb blasts. The commission also documented effects on unborn fetuses, including microcephaly and mental retardation. In 1956, Stewart et al reported increased frequency of leukemia in children with history of radiation exposure during fetal life. In 1975, the ABCC was reorganized and renamed the RERF (Radiation effects and research foundation), funded equally by the United States of America and Japan. The RERF continues its work on genetics, cancer induction and other delayed effects of ionizing radiation.

1. Radiation Protection
Dr. Zahid Qayoom
PG Radiodiagnosis,
SKIMS, Srinagar

2. Introduction
• Radiation can be defined as a packet of energy.
• Ionizing and Non-ionizing
• Nonionizing radiations do not affect at molecular
levels. They may cause electrical shocks and
burns.
• Ionizing radiations, such as X-rays have power to
penetrate inside the body.

3. Introduction
• Since X-rays are very small in size, some of them
can cross the body without interaction, some will
interact with atoms and lose energy completely,
others will get scattered and come out from the
body.
• Thus, the transmitted X-rays have energy from
zero to a maximum value and when they fall on a
two dimensional image receptor and deposit their
energy, they create an image of the organ
exposed.

4. HISTORICAL
PERSPECTIVE

5. • In November 1895, Wilhelm Roentgen discovered
X-rays.
• Within few months of Roentgen’s discovery, eye
complaints and severe progressive dermatitis were
reported.
• In 1896, one of Edison’s assistants Clarence E Dally,
involved in the production of X-ray tubes, who had
been using his own hand to test their output,
developed ulcerating carcinoma of his repeatedly
exposed left hand.

6. • Delayed effects of radiation began to be documented only 20
years after their initial discovery, through individual case
reports.
• In 1927, Germline mutation as a delayed effect of ionizing
radiation was documented by Muller which won him the Nobel
Prize.
• In 1928, Murphy reported 14 cases of microcephaly and mental
retardation in children of mothers who had received pelvic
radiotherapy early in pregnancy.
• In 1929, Murphy and Goldstein documented 16 more patients
with similar defects of microcephaly and mental retardation
among children whose mothers had received pelvic
radiotherapy early in pregnancy

7. • In 1940s and 1950s, it was a common practice to
treat ankylosing spondylitis patients with radiation. It
was a permanent cure and remained the treatment of
choice for approximately 2 years, until it was
discovered that some of the patients who had been
cured by radiation were dying from leukemia.
• In 1942, Dunlap reported radiation induced leukemia
in radiologists and other radiation workers.

8. • In 1947, the Atom Bomb Casualty Commission (ABCC)
was established, which subsequently reported the
incidence of genetic effects, mutations, cataracts,
leukemias and other malignancies in the population
exposed in Hiroshima and Nagasaki atomic bomb blasts.
• The commission also documented effects on unborn
fetuses, including microcephaly and mental retardation.
• In 1956, Stewart et al reported increased frequency of
leukemia in children with history of radiation exposure
during fetal life.

9. • In 1975, the ABCC was reorganized and renamed
the RERF (Radiation effects and research
foundation), funded equally by the United States
of America and Japan.
• The RERF continues its work on genetics, cancer
induction and other delayed effects of ionizing
radiation.

10. INTERACTION OF
RADIATION WITH
MATTER

11. • Medical imaging involves use of electromagnetic
waves located near one end of the electromagnetic
spectrum.
• At one end of the spectrum are the long-wavelength
and relatively innocuous radio- and microwaves.
• At other end are short-wavelength, high-energy X-
rays, gamma rays and cosmic rays. This energy has
the capacity to be harmful to biologic tissue because
it carries the potential to displace electrons from its
energy level or shell around the nucleus. This can
lead to ionization. (Ionizing radiation)

12. • There are three major ways in which radiation is
absorbed, especially X-rays, and results in
ionization:
• the photoelectric effect
• the Compton effect
• Pair production.

13. Photoelectric effect

14. Compton effect

15. Pair Production

16. • At low energies (30–100 kev), as in diagnostic
radiology, the photoelectric effect is predominant.
• At intermediate energies, as used in therapeutic
radiology, the Compton effect dominates.
• At energy levels above 1.02 MeV, the photons
may be absorbed through pair production.

17. BIOLOGICAL EFFECT
OF RADIATION

18. • X-ray energy used in the diagnostic radiology varies from
25 to 125 kVp
• Sufficient to produce ionization inside the human body.
• Creates damage to the DNA by direct and indirect
mechanisms.
• In the direct mechanism, the X-ray hits the DNA molecules
directly. DNA molecule gets ionized, resulting in damage.
• In indirect mechanism, water molecules absorb the X-ray
energy and dissociate into H+ and OH–. OH- free radical is
highly reactive. It reacts with DNA and creates damage.
• 60–70% of radiation-caused DNA damage is due to OH-
free radical.

19. • These damages can lead to:
• Slow down in the cell synthesization.
• Delay in repair mechanism that will delay the cell
cycle progression.
• Delays in cell proliferation.
• Mutation of the cell.
• Cell transformation.
• Death of the cell.

20. • The cells are most sensitive to radiation during
Mitosis (i.e. M phase) and G2 phase (i.e. Premitosis
or RNA synthesis).
• Least sensitive during S phase (DNA synthesis).
• So, slow developing cells are less sensitive to
radiation in comparison to the fast/rapid developing
cells.
• Children do not have as many cells as adults, but they
have greater proportion of dividing cells.
• Thyroid gland is one of the most radiation-sensitive
parts of the body, especially in babies and children.

21. Stochastic and Nonstochastic
(Deterministic) Effects

22. • Deterministic effects are the result of excessive
cell death.
• E.g., skin erythema, epilation, necrosis, lens
cataract formation.
• Because these effects occur only after a critical
mass of cells have died, they have a known
radiation exposure threshold.

23. • Stochastic effects are random events which are
not dose-related.
• Carcinogenesis and hereditary effects.
• As the dose increases the probability of
occurrence of stochastic effect also increases.
There is a nonthreshold linear relationship
between absorbed dose and probability of effect.
• Basis for the practice of exposures being kept As
Low As Reasonably Achievable (ALARA)

24. Measurement of
Radiation

25. Exposure
• Amount of X-rays or gamma rays that produces a
specific amount of ionization in a unit of air under
standard temperature and pressure.
• Traditional unit is Roentgen (R).
• 1 R = 2.58 × 10–4 coulomb/kg of air.
• R is valid for X-rays and gamma rays with energy
up to 3 MeV, & their interaction with air only.

26. Absorbed Dose
• Quantity of radiation energy absorbed per unit
mass of tissue.
• The unit of absorbed dose is joule per kilogram (J
kg–1) and a special name given to this in SI unit is
gray. 1 gray (Gy) = 1 joule/kg
• The traditional unit of absorbed dose is rad
(radiation absorbed dose)
• 1 Gy = 100 rad
• 10 mGy = 1 rad

27. • All types of radiation do not have the same potential
for producing biological change.
• For example, one rad of one type of radiation might
produce significantly more radiation damage than
one rad of another type.
• So, it is necessary to develop a distinction between
the biological impact and the physical quantity of
radiation.
• Dose Equivalent & Effective Dose Equivalent
(Effective Dose) are two quantities which take care
of this.

28. Dose Equivalent
• Also called radiation protection unit as it takes into account the
potential of the radiation to cause biological damage.
• Various types of radiation have been assigned a “quality factor”
called radiation weighing factor (WR).
• WR for X-rays, gamma rays, beta rays and electrons is 1
• For alpha particles, WR is 20
• Equivalent dose = Absorbed dose × WR
• The traditional unit for equivalent dose is rem.
• The SI unit is sievert (Sv).
• 1 Sv = 100 rem
• 10 mSV = 1 rem
• For X-rays WR = 1 and hence, 1 mGy = 1 mSv

29. • Exposure, absorbed dose and dose equivalent,
although each expresses a different aspect of
radiation, they all express radiation concentration.
• For the types of radiation used in diagnostic
procedures, the factors that relate the three
quantities have values of approximately 1 in soft
tissue.
• Therefore, an exposure of 1 R produces an
absorbed dose of approximately 1 rad, which in
turn, produces a dose equivalent of 1 rem.

30. Effective Dose Equivalent (Effective Dose)
• Radiosensitivity of various tissues is different.
• Tissue have been assigned a tissue weighting factor
(WT) which represents the detriment (risk) of the
radiation exposure to that tissue with respect to the
uniform whole body radiation exposure.
• Effective Dose Equivalent (Sv) = Dose Equivalent
(Sv) × WT
• Effective dose has similar units as that of equivalent
dose, i.e. traditional unit is rem and SI unit is sievert
(Sv)

31. Effective Dose Equivalent (Effective Dose)

35. Malignancies associated
with Radiation exposure

36. • Leukemia:
• Two types of adult leukemias are associated with
radiation exposure - acute and chronic myeloid
leukemias.
• Radiation exposure during childhood results in an
increased incidence of acute lymphatic leukemia.
• The latency period of leukemia is a minimum of 2
years, peaks at 7–12 years and returns to zero at
about 30 years.

37. • Other radiation-induced cancers:
• Skin
• Lung
• Bone
• Blood dyscrasias
• Meningiomas
• Osteosarcomas
• Breast carcinoma
• Thyroid carcinoma

38. DETERMINISTIC EFFECTS AS
DOCUMENTED
FROM RADIATION ACCIDENTS

39. Acute Total-body Irradiation
• At doses in excess of 100 Gy to the total body, death
usually occurs within 24–48 hours from neurologic and
cardiovascular failure. This is known as the cerebrovascular
syndrome.
• At doses between 5 and 12 Gy, death may occur in a matter
of days, as a result of the gastrointestinal syndrome.
• At total-body doses between 2 and 8 Gy, death may occur
several weeks after exposure and is due to effect on the
bone marrow, which results in the hematopoietic syndrome.
The threshold for this syndrome is 1 Gy.
• Mean lethal dose or LD50: estimates of LD50 for humans is
3 to 4 Gy

40. Chronic Radiation Effects
• Central nervous system:
• Mild encephalopathy, focal neurological changes
and transverse myelitis are known side effects of
CNS irradiation.
• A unique late effect of cranial radiation combined
with chemotherapy known as
leukoencephalopathy, has been described as a
necrotizing reaction and is usually noted at 4–12
months.

41. Chronic Radiation Effects
• Skin:
• Erythema
• Desquamation
• Thinning of epidermis
• Pigmentation
• Hair loss

42. Chronic Radiation Effects
• Heart and blood vessels:
• Asymptomatic pericardial effusion
• Chronic constrictive pericarditis
• Pancarditis

43. Chronic Radiation Effects
• GIT:
• Terminal ileum is the most commonly affected
part.
• Changes include fibrosis, perforation, fistula
formation, stenosis, etc.

44. Chronic Radiation Effects
• Hematopoetic system:
• Fatty replacement of marrow occurs above a
threshold of 50 Gy.
• Eye:
• Cataract has been recorded at 2 to 8 Gy of single
exposure
• Bladder:
• Interstitial fibrosis, telangiectasia, ulceration and
reduced capacity

45. Radiation Effects on Embryo / Fetus
• Since embryo/fetus has rapid developing cells,
they are more sensitive to radiation than the adult.
• CNS:
• Exencephaly
• Microcephaly
• Mental retardation
• Skull malformations
• Hydrocephalus

46. Radiation Effects on Embryo / Fetus
• Ocular malformations:
• Absence of eyes
• Microphthalmia
• Absence of lens
• Cataract
• Skeletal malformations:
• Stunting
• Cleft palate
• Club feet
• Deformed arms
• Spina bifida
• Other malformations are genital malformations

47. Radiation Effects on Embryo / Fetus
• Animal data suggest that doses of 5–10 rad (50–100
mGy) received before embryonic implantation may
result in prenatal death.
• Microcephaly has been the primary anomaly reported
in children of the survivors of Hiroshima and
Nagasaki, who sustained in utero radiation exposure.
Most sensitive period for this defect is 2–15 weeks
after conception.
• In fetuses who received in utero exposure during the
later half of this period, i.e. 8–15 weeks, severe
mental retardation and intellectual deficits are also of
concern at low doses as low as 10 rad (100 mGy).

48. Radiation Effects on Embryo / Fetus

49. Protection of Patient,
Staff and
Public from Radiation

50. Radiation Risk
• Radiation risk calculations are based on the type of
radiation, amount of energy absorbed, and which part of the
body these energies are deposited in.
• The probability of cancer induction is low at low dose but
never zero theoretically and therefore calls for the
optimisation of radiation doses for all radiological
investigations (ALARA)
• It is not possible to differentiate or detect the cancer caused
by diagnostic X-rays from cancer caused by other factors.
• The latency period of cancer induction may be in years or
even in decades. If the low level of radiation exposure has
occurred today, its effect as a cancer may be expressed after
years of exposure.

51. Radiation Protection Guidelines and
LNT Model
• In 1950s, the scientific group created the radiation
protection guidelines.
• At that time no one really knew the effect of low dose of
radiation.
• It was decided to assume that the relation between the
radiation dose and its effects are linear and proportional.
• It was also decided that any dose, no matter how small,
could bring an effect.
• This is called a linear no-threshold (LNT) model.
• Still this LNT model is in use to set radiation protection
guidelines.

52. Radiation Protection Guidelines and
LNT Model
• Effect of radiation at low doses is a controversial
topic since it is difficult to get ideal
epidemiological data.
• Cancer induction may be the only effect at low
dose of radiation.
• On the other hand there are researchers and their
preliminary experimental results which may
indicate about the existence of beneficial effect of
low-level radiation (called radiation hormesis).

53. Radiation Protection Guidelines and
LNT Model

54. Radiation Protection Guidelines and
LNT Model
• At present it is thought prudent to consider low-level radiation having
linear relationship with risk (without having any threshold of a minimum
dose) which signifies that even low-level radiation entails some risk.
• Every country has a regulatory authority to set the guidelines regarding
radiation protection, make laws and to enforce them.
• These guidelines are based on LNT model and made in such a way that if
followed properly, patient, staff and public all are protected.
• We must obey them.
• Atomic Energy Regulatory Board (AERB), Mumbai is the competent
authority to enforce radiation safety in practice in India.
• Radiation safety in handling of radiation generating equipment is
governed by section 17 of the Atomic Energy Act, 1962, and the
Radiation Protection Rules (RPR), GSR - 1601, 1971 issued under the
Act.

55. Radiation Protection Survey and Program
• The administration is expected to appoint a Radiation safety
committee (RSC), and a radiation safety officer (RSO).
• Every department should have an RSO.
• In India, AERB has specified duties of the RSO.
• He/she shall implement all radiation surveillance measures,
conduct periodic radiation protection surveys, maintain proper
records of periodic quality assurance tests, and personnel doses,
instruct all workers on relevant safety measures, educate and
train new entrants, and take local measures, including issuance
of clear administrative instructions in writing, to deal with
radiation emergencies.
• The RSO should also ensure that all radiation measuring and
monitoring instruments in his/her custody are properly
calibrated and maintained in good condition.

56. Radiation Protection Survey and Program
• RSC should comprise of a radiologist, a medical
physicist, a nuclear medicine personnel, a senior
nurse and an internist.
• It is the duty of RSC to perform regular radiation
protection surveys & recommend any corrective
measures to be taken.

57. Radiation Protection Survey and Program

58. Principles of Radiation Protection

59. Principles of Radiation Protection
• The current radiation protection standards are
based on three general principles, which are
recommendations of the International
Commission on Radiological Protection (ICRP):
• Justification
• Optimization
• Dose limitation

60. Principles of Radiation Protection
• Justification:
• For example, benefit to risk ratio is high for CT
brain in cerebrovascular haemorrhage and low in
screening mammography in women below 35
years.

61. Principles of Radiation Protection
• Optimization:
• Radiation sources and installations should be
provided with the best available protection and
safety measures under the prevailing
circumstances, so that the magnitudes and
likelihood of exposures and the numbers of
individuals exposed be kept as low as reasonably
achievable (ALARA)

62. Principles of Radiation Protection
• Dose limitation:
• No radiation dose, however low, can be considered absolutely safe. Although
this may be an overestimation of the true radiation effects at low-dose levels, it is
preferable to hold the model and it is the basis for radiation protection standards
today.
• Maximum permissible dose equivalent (MPD): The maximum dose of ionizing
radiation which an individual may accumulate over a long period of time with a
negligible risk of significant body or genetic damage.
• MPD = 5(N-1)R
• N is age in years more than 18 years and R is the exposure in Roentgens
• Unit of MPD is rem
• The newer recommendation is MPD = Age in years × 1 rem, i.e. the individual
effective dose for a lifetime should not exceed the value of his/her age.

63. Principles of Radiation Protection
• The triad of radiation protection measures is
“time-distance-shielding”
• Time:
• Exposure = Exposure rate × Time
• If the exposure time is kept short, then the
resulting dose to the individual is small.

64. Principles of Radiation Protection
• Distance:
• The exposure to the individual decreases inversely
as the square of the distance.
• This is known as the inverse square law.
• When the distance is doubled the exposure is
reduced by a factor of four.

65. Principles of Radiation Protection
• Shielding:
• X-ray tube shielding
• Room shielding
X-ray equipment room shielding
Patient waiting room shielding
Control room shielding
• Personnel shielding
• Patient shielding

66. Principles of Radiation Protection
• Three types of radiations have to be considered in
radiation protection:
• Useful beam (Primary beam)
• Leakage radiation
• Scattered radiation

67. X-ray Tube Shielding (Source Shielding)
• X-rays produced in the tube are scattered in all
directions.
• So, X-ray tube housing is lined with thin sheets of
lead to protect both patients and personnel from
leakage radiation.
• Manufacturers of X-ray devices are required to shield
the tube housing so as to limit the leakage radiation
exposure rate to less than 0.1 R hr–1 at 1 meter from
the tube anode.
• AERB recommends a maximum allowable leakage
radiation from tube housing not greater than 1 mGy /
hour at 100 cm.

68. Room Shielding (Structural Shielding)
• Lead-lined walls protect individuals located
outside the X-ray rooms from unwanted radiation.
• A 2-mm lead is equivalent to
25 mm layer of high quality barium plaster
225 mm of solid brick
150 mm of concrete
½ brick thickness
½ inch plaster

69. Room Shielding (Structural Shielding)
• There are two types of protective barriers:
• Primary barrier:
• It is one which is directly struck by the primary or the useful beam.
• Should consist of 1/16 inch lead extending 7 feet from the floor, when
the X-ray tube is 5–7 feet from the wall.
• This barrier also takes care of the leakage radiation.
• Secondary barrier:
• It is one which is exposed to stray radiation either by leakage from X-ray
tube or by scattered radiation from the patient.
• Should consist of 1/32 inch of lead. This secondary barrier extends from
the top of the primary barrier to the ceiling and should overlap the
primary barrier at least 0.5 inches at the seam.

70. Room Shielding (Structural Shielding)
• Control area:
• The area routinely occupied by radiation workers
who are exposed to an occupational dose.
• For control area, the shielding should be such that it
reduces exposure in that area to less than 2.6
mC/kg/week.
• Uncontrolled areas:
• Not occupied by occupational workers.
• The shielding should reduce the exposure rate to less
than 26 mC/kg/week.

71. Room Shielding (Structural Shielding)
• Half-value layer (HVL):
• Thickness of a specific substance that when
introduced into the path of a beam of radiation,
reduces the exposure rate by 50%.
• For example, if the exposure at a point is 3.2 R/week
and the permissible exposure is 0.1 R/week, the
required number of HVLs calculated, which will
reduce 3.2 R/week–0.1 R/week, is 5.
• If the HVL of the beam is 0.25 of lead, the barrier
thickness would be 1.25 mm (0.25 × 5 = 1.25 mm)

72. Room Shielding (Structural Shielding)

73. Shielding of the X-ray Control Room
• Control room of X-ray equipment is a secondary
protective barrier.
• The walls and viewing window of the control
booth should have lead equivalents of 1.5 mm.
• Control booth should not be located where the
primary beam falls directly, and the radiation
should be scattered twice before entering the
booth.

74. Shielding of the X-ray Control Room
• AERB recommends:
• The control panel of diagnostic X-ray equipment operating at 125 kVp or
above (as in CT) is installed in a separate room located outside but
contiguous to the X-ray room and provided with appropriate shielding,
direct viewing and oral communication facilities between the operator
and the patient.
• In case of X-ray equipment operating up to 125 kVp, the control panel
can be located in the X-ray room itself. The distance between control
panel and X-ray unit/chest stand should not be less than 3 m for general
purpose fixed X-ray equipment.
• In mobile radiography, the technologist should remain at least 2 m from
the patient, the X-ray tube and the primary beam during exposure.
• The size of the CT room housing the gantry of the CT unit should not be
less than 25 m2.

75. Personnel Shielding
• Personnel should remain in the radiation
environment only when necessary.
• The distance between the personnel and the
patient should be maximized when practical.
• Shielding apparel should be used as and when
necessary which comprise of lead aprons, eye
glasses with side shields, hand gloves and thyroid
shields.

76. Personnel Shielding
• Lead aprons are classified as a secondary barrier to the effects
of ionizing radiation.
• These aprons protect an individual only from secondary
(scattered) radiation, not the primary beam.
• 0.25 mm lead thickness attenuates 66% of the beam at 75 kVp
& 1 mm attenuates 99% of the beam at same kVp.
• For general purpose radiography, the minimum thickness of lead
equivalent in the protective apparel should be 0.5 mm.
• Women radiation workers should wear a customized lead apron
that reaches below midthigh level and wraps completely around
the pelvis. This would eliminate an accidental exposure to a
conceptus.
• The minimum protective lead equivalents in hand gloves,
gonadal shields and thyroid shields should also be 0.5 mm.

77. Personnel Shielding
• Care of the lead apparel:
• Lead aprons should not be abused, such as by
dropping them on the floor, piling them in a heap or
improperly draping them over the back of a chair.
• All of these actions can cause internal fracturing of
the lead & compromise the apron’s protective ability.
• When not in use, all protective apparel should be
hung on properly designed racks.
• Protective apparel also should be radiographed for
defects such as internal cracks and tears at least once
a year.

78. Patient Shielding
• Radiation protection of the patient involves both
technical and medical decisions.
• The reduction in radiation dose by changes in the
equipment will result in a more consistent
reduction .
• While, reduction due to radiological technique
need constant effort to maintain the benefit.

79. Patient Shielding
• Beam filtration:
• Causes lower energy photons to be absorbed by the filters.
• Absorption primarily takes place with X-rays of less than 40
keV of energy and virtually all X-rays below 10 keV are
absorbed.
• These low energy X-rays contribute to patient dose without
contributing to the image.

80. Patient Shielding
• Beam collimation:
• The area of the patient exposed to the X-ray beam
should be limited to the area of clinical interest.
• Substantially reduces unnecessary patient exposure.
• The amount of scattered radiation that reaches the
image receptor is also decreased & the resulting
images have better contrast.
• The table top should be one which allows a high
beam transmission. Carbon fiber material is generally
used.

81. Patient Shielding
• Image receptors:
• Intensifying screen was designed to optimize absorption of
the radiation by converting absorbed X-ray energy into
visible light, which would be more readily absorbed by the
film than the more energetic X-ray photons.
• The advent of fluorescent intensifying screens, which act as
image amplifiers and their use with X-ray film, which is
highly sensitive to the visible light photons, significantly
reduce the absorbed dose to the patient while still
maintaining the image quality.
• The image intensifier tubes, in use today, also have efficient
input phosphors that play a role in reducing the dose to the
patient.

82. Patient Shielding
• Source to image receptor distance (SID):
• The dose to the patient is reduced when the
source-to-skin-distance (SSD) is increased and the
SSD is related to the source-to-image-receptor-
distance (SID).
• The recommended source-to-skin-distance for an
under couch fluoroscopic tube is a minimum of 30
cm and more when possible.

83. Patient Shielding
• Antiscatter grids:
• Reduce scattered radiation reaching the film, thus
improving the quality of the resulting radiograph
and reducing chances of repeat exposures.

84. Patient Shielding
• Fluoroscopy X-ray equipment:
• Shall be so constructed that leakage radiation through the protective tube
housing in any direction shall not exceed a dose of 1 mGy in one hour at
a distance of 1.0 m from the X-ray target when the tube is operating at
the maximum rated kVp.
• Protective lead glass covering of the fluorescent screen shall have a lead
equivalent thickness of 2.0 mm for units operating up to 100 kVp.
• Protective flaps shall be installed, having lead equivalence of not less
than 0.5 mm and sufficient dimensions to protect the radiologist.
• X-ray tube and fluoroscopic screen shall be rigidly coupled and aligned
so that both move together synchronously and the X-ray beam axis
passes through the center of the screen in all positions of the tube and
screen.
• Tube housing should be provided with a field-limiting diaphragm.

85. Patient Shielding
• The focus-to-table top distance should be not less
than 30 cm for fluoroscopy units.
• Fluoroscopy timer
• Foot-switch and visual indicator
• Table-top exposure in any case shall not exceed 5
cGy per minute.

86. Patient Shielding
• Technique:
• Repeat exposures to the patient give an additional radiation
dose.
• Optimum film processing helps to avoid repeat examinations.
• Use the highest kVp possible.
• The NCRP recommends that the kVp and mA should be visible
to the person doing the fluoroscopy at all times.
• Intermittent fluoroscopy rather than continuous fluoroscopy is
often adequate and should be followed.
• The beam should be collimated the smallest that still shows.
• Magnification mode should be avoided as this increases the
dose.

87. Patient Shielding
• Pregnancy:
• Ten-day rule: In a female of reproductive age
group, the radiograph should be carried out during
the first 10 days of the menstrual cycle to avoid
irradiating any possible pregnancy.
• The greatest risk to the fetus of chromosomal
abnormalities and subsequent mental retardation
is between 8 and 15 weeks of pregnancy and
examinations involving radiation to the fetus
should be avoided during this period.

88. Patient Shielding

89. Patient Shielding
• Recommended dose limits to pregnant women:
• Both ICRP and AERB recommend that, once
pregnancy is established, the dose equivalent to
surface of pregnant woman’s abdomen should not
exceed 2 mSv for the remainder of the pregnancy.

90. Computed tomography radiation
exposure and dose modulations

91. Computed tomography radiation
exposure and dose modulations

92. Computed tomography radiation
exposure and dose modulations

93. Computed tomography radiation
exposure and dose modulations
• Techniques for Controlling radiation Dose at CT:
• Automated exposure control (AEC)
• Modifying the acquisition parameters.
• Reducing the Milliampere-seconds Value.
• Increasing Pitch.
• Optimum Tube Potential.

94. Personnel dosimetry
• Monitoring of individuals who are exposed to
radiation during the course of their work.
• Personnel dosimetry policies need to be in place
for all occupationally-exposed individuals.
• The data from the dosimeter are reliable only
when the dosimeters are properly worn, receive
proper care, and are returned on time.
• Dosimeters used for personnel monitoring have
dose measurement limit of 0.1–0.2 mSv

95. Personnel dosimetry
• Thermoluminescent Dosimetry:
• Thermoluminescence is the property of certain
materials to emit light when they are stimulated
by heat.
• Materials, such as lithium fluoride (LiF), lithium
borate (Li2B4O7), calcium fluoride (CaF2), and
calcium sulfate (CaSO4) have been used to make
TLDs.
• The TLD can measure exposure to individuals as
low as 1.3 µC/kg (5 mR).

96. Thank You