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