effects of radiation dr. usha introduction natural sources (80%): cosmic rays, ultraviolet rays,...
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EFFECTS OF RADIATION
DR. USHA
Introduction
Natural sources (80%): cosmic rays, ultraviolet rays, natural isotopes (radon gas).
Artificial sources(20%): Radio waves, Microwaves, Instruments used in medicine & dentistry.
Types of radiation
Ionizing radiation Non-ionizing radiation
Ionizing radiation:
Is the energy emitted in the form of electromagnetic waves or particles.
Electromagnetic waves: Gamma rays, X-Rays, Microwaves, Radio waves.
Particulate radiation: Alpha, Beta, Gamma, Protons, Neutrons.
Unit of radiation
Roentgen Rad Gray Rem
Mechanism of radiation injury
1. Direct:- damage DNA, RNA, Proteins
2. Indirect:- causes electrolysis of water, leading to formation of free radicals which can induce cell Injury, cell death, DNAmutations.
Critical Target is DNACritical Target is DNA
CellCellNucleus contains DNANucleus contains DNANucleus contains DNANucleus contains DNA
DNA is packaged on chromosomesDNA is packaged on chromosomesDNA is packaged on chromosomesDNA is packaged on chromosomesDNA double stranded helixDNA double stranded helixDNA double stranded helixDNA double stranded helix
Factors affecting radiation response
1. Tissue sensitivity:-
Human tissues can be classified as
a. Highly radiosensitive-labile cells
b. Moderately radiosensitive-stable cells
c. Radioresistent- permanent cells
Factors continued
2.Total dose:-<0.5 Gy- No consequences0.5-2 Gy – subclinical acute radiation
syndrome2-6 Gy – hematopoietic radiation syndrome3-10 Gy – gastrointestinal radiation
syndrome>10 Gy – cerebral radiation syndrome
Factors cont..
3. Dose rate:
Single large dose can cause greater damage than divided doses because fractionated doses allow time for cellular repair.
Factors cont..
4. Hypoxia:Ionizing radiation causes radiolysis of water
or interact with the oxygen.Therefore hypoxic tissue are relatively
resistant to radiation injury.Eg. The center of rapidly growing tumors is
poorly vascularized & hence hypoxic, making radiotherapy less effective.
Biological effects of radiation
1.Early
2.Delayed
Acute dose
An acute radiation dose is defined as a large dose (10 rad or greater, to the whole body) delivered during a short period of time. .
Acute radiation syndromeAcute Whole
body dosesymptoms prognosis
subclinical <200 rad Mild nausea &
vomiting
100% survival
Hematopoitic 200-600 rad Petichae, hemorrhage, infections
Require BMT
Gastrointestinal 600-1000rad Severe nausea, vomiting diarrehea, hemorrahage
Shock & death in 10-14 days
CNS >10000 rad Confusion, somnolence, coma, delirium
Death in 14- 36 hrs
Delayed effects
1.Carcinogenesis
2. Abnormalities of growth & development
3. Degenerative lesions of most major organ systems.
1. Carcinogenesis
Radiation directly or indirectly damages DNA in the form of chromosomal breakage, translocation, or point mutations.
Eg: leukemias/lymphomas Thyroid cancer Osteosarcoma Lung cancer Liver angiosarcoma
2.Abnormalities of growth & development
1. Pre implantation embryo: lethal
2. Stage of organogenesis: congenital malformations
3. Fetal period: functional abnormalities of CNS &reproductive system
4. Postnatal period :bone growth & maturation is retarded
3.Organ changes
Blood vessel: narrowing of blood vessel because of subintimal fibrosis,fibrosis of media.
Skin: CHRONIC RADIATION DERMATITIS- increased pigmentation, epidermal atrophy, dermal fibrosis, loss of hair & skin cancer
Organ changes cont..
Lungs: DELAYED RADIATION PNEUMONITIS- intra alveolar & interstitial fibrosis.
Heart: myocardial fibrosis & constrictive pericarditis.
GIT: ulceration & atrophy of mucosa, fibrosis that cause strictures & obstruction
Organ changes cont… Gonads: testicular atrophy in males,
ovarian degeneration in females. Eyes: cataract Brain: focal necrosis & degeneration of
white matter. Spinal cord: necrosis, demyelization &
paraplegia- transverse myelitis Hematopoietic tissue: B.M suppression
Morphology of cells in radiation injury
Nuclear changes: nucleus appears pleomorphic because of nuclear swelling & condensation & clumping of chromatin.
Cytoplasmic changes: cytoplasmic swelling, mitochondrial distortion, degeneration of ER.
Ultraviolet radiation
3 types - UV A
UV B
UV C
OZONE- absorbs most of the UV B & UV C
UV TYPE ACUTE CHRONIC
UV A Erythema, pigmentation, dermal inflammation
Tanning, skin cancer ?
UV B Erythema, apoptosis of keratinocytes,depletion
of langerhans cells
Tanning, solar elastosis, premature aging, actinic keratosis, skin cancer
UV C
------------
?skin cancer
Skin cancers
Basal cell carcinoma Squamous cell carcinoma melanoma
THE END