Transcript Module III.2.6-Effects of partial body irradiation

IAEA Post Graduate Educational Course in Radiation Protection and Safety of Radiation Sources
Biological Effects of Ionizing Radiation
Deterministic effects
Effects of partial body irradiation
Lecture
IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources
Introduction
 Partial body irradiation may cause local
radiation injury of the part of the body
 Sources of data for deterministic effects in
man:
 side effects of radiotherapy
 effects on the early radiologists
 effects amongst survivors of the atomic
bombs at Hiroshima and Nagasaki in Japan
 consequences of severe accidents
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Content
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Threshold doses for deterministic
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effects in different organs
Radiation-induced damage of the:
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Skin
Eye
Lung
Gonads
Thyroid
Skeleton
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Overview
 Partial body irradiation may cause
local radiation injury of the part of
the body
 Possible target:
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Skin
Thyroid
Lung
Eye lens
Gonads, etc
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Threshold of occurrence for local
injury
Organ or
tissue
Dose in
less than 2
days, Gy
Deterministic effects
Type of effect
Time of
occurrence
Skin
3
Erythema
1 – 3 weeks
Thyroid
5
Hypothyroidism
1st – several
years
Lens of the
eye
2
Cataract
6 months several years
Gonads
3
Permanent
sterility
weeks
Lung
8
Pneumonitis
1-3 months
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Time of Onset of Clinical Signs of Skin
Injury vs Dose Received
Symptoms
Erythema
Epilation
Dry desquamation
Moist desquamation
Blister formation
Ulceration
Necrosis
Dose range
(Gy)
3-10
>3
8-12
15-20
15-25
>20
>25
Time of onset
(day)
14-21
14-18
25-30
20-28
15-25
14-21
>21
Radiation injury of the skin: acute
phase
 Inflammation: redness (erythema), swelling
(oedema), elevated temperature
 Passive tissue compression: thrombosis,
circulation disorders (insufficient blood supply)
 Tissue atrophy, necrosis: pain, acute ulceration
 moderate doses ( > 20 Gy): epidermal cell depletion
(denudation) due to the mitotic death of the epidermal
cells basal and viable upper layers with consecutive dry
or moist desquamation, blistering of the epidermis and
secondary dermal ulceration
 very high doses (>100 Gy surface dose): acute dermal
necrosis within 2-3 weeks (interphase death of
endothelial and fibroblast type cells; sometimes moist
desquamation and blisters)
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Radiation injury of the skin: late
phase
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Epidermal and dermal atrophy: (fragile skin)
Insufficient blood supply
Late necrosis with skin ulceration
Occlusion of lymphatic vessels with local lymph
stagnation: pain, late oedema
Hyperkeratotic and fibrotic degeneration of the
skin
Decreased immunological defence of the skin
with increased sensitivity against infections, etc
Persistent or recurring pain
Increased risk of skin malignancies
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Radiation injury of the eye
 Observations:
 X-ray treatment of eye tumors
 Radiation injuries:
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Lid erythema
Conjunctivitis
Cataract
Retinopathy
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Cataract
 Cataract - any detectable change of the
normally transparent lens of the eye
 Reason of development:
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Some abnormal metabolic disorder
Chronic ocular infection
Trauma
Old age
Ionizing radiation (radiation-induced cataract)
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Radiation-induced cataract
 The threshold dose following a single exposure
of low-LET radiation is 2 Gy, for neutrons 0.2 Gy
 Lowering the dose rate or extending the exposure
period increases the ED50 value to an average of
9.3 Gy
 Estimated latency periods: 6 month to 35 years
 Doses of less than 0.1 Sv/year are not thought to
present appreciable risk for detectable visual
impairment
 Occupational exposure limit for the eye is 0.15 Sv
(ICRP-60)
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Radiation-induced retinopathy
 Threshold dose of retinal damage: 15 - 35 Gy
depending on: radiation quality, dose rate,
fractionation, fraction size
 threshold for visual impairment: ~ 50 Gy
 occurrence: 35 Gy ~ 10%; 45 Gy ~ 66 %; 80 Gy ~ 100 %
 Latency period: 6 months to 3 years
 Clinical manifestation:
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microaneurysms of the capillaries
“cotton-wool spots”
intraretinal haemorrhages, and
leakage of retinal vessels with exudates
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Radiation-induced hypothyroidism
 Threshold dose – 5 Gy of acute
exposure within 2 days
 Latent period – years
 Pathophysiological mechanism
involved:
 direct lesions to follicular cells
 alterations of vascular system
 immunological reactions
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Deterministic radiation injury of
the lung
 Pheumonitis
 Threshold dose – 8 Gy of acute
exposure
 Latent period – 1-3 months
 Fibrosis
 At the late stage and as a consequence
of acute pneumonitis
 Latent period – 6 months
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Radiation-induced pulmonary reactions
 Phases of development:
 Latency
 degenerative changes of pneumocytes and of
endothelial cells
 Acute pneumonitis
 dose-dependent leakage of proteins in the alveolar
space
 thickening of alveolar septa
 oedema of the interstitium, and
 changes to the capillaries in the number of type II
pneumocytes and alveolar macrophages
 Fibrosis
 capillary loss
 further decrease in the number of type I pneumocytes
 increased collagen deposition
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Deterministic radiation injury of
the gonads
 Sterility:
 Temporary
 Permanent
 Target organ:
 Testes
 Ovarium
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Deterministic radiation injury of
the gonads (Cont’d)
Organ / consequence
of exposure
Testes
 temporary sterility
 permanent sterility
Ovary
 permanent sterility
Threshold absorbed dose of exposure
Acute, Sv
Protracted, Sv/year
0.15
3.0
0.4
2.0
2.5
0.2
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Deterministic radiation injury of
the skeleton
 Threshold dose – 5-10 Gy
 Children bones are more sensitive
 The severity of radiation-induced damage
to growing bone depends on:
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the total radiation dose
fractionation
dose homogeneity
volume irradiated
symmetry of the volume irradiated
patient's age, etc
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Summary
 This lecture presented materials about
effects of partial body irradiation
 The following topics were covered in
the lecture: threshold doses for
deterministic effects in different
organs, radiation-induced damage of
the skin, eye, lung, gonads, thyroid and
skeleton
 Comments are welcomed
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Where to Get More Information
 UNSCEAR, Sources and Effects of
Ionizing Radiation, 2000 Report to the
General Assembly with Scientific
Annexes, United Nations, New York,2000
 IAEA - WHO. Diagnosis and treatment of
radiation injuries, Safety Reports Series
No. 2, IAEA, Vienna, 1998
 Hopewell JW. The skin: It's structure and
response to ionizing radiation. Int J
Radiat Biol 1990; 57:751-73
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