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 DNA Cell Nucleus contains DNA DNA is packaged on chromosomes DNA 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 consequences Gy – subclinical acute radiation syndrome 2-6 Gy – hematopoietic radiation syndrome 3-10 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 syndrome AcuteWhole body dose symptomsprognosis subclinical<200 radMild nausea & vomiting 100% survival Hematopoitic rad Petichae, hemorrhage, infections Require BMT Gastrointestinal radSevere nausea, vomiting diarrehea, hemorrahage Shock & death in days CNS>10000 radConfusion, somnolence, coma, delirium Death in 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 TYPEACUTECHRONIC 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

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