33 - Ionising Radiation Flashcards
Radiation
Energy propagated in either electromagnetic or particulate form
Ionising radiation
- Carries sufficient energy to produce ionisation in the tissues which absorb it (by displacing electrons from atoms)
- Short wave length/high frequency waves
Electromagnetic energy
- Bundles of energy propagated by wave motion
- Continuous spectrum
Particulate radiation
Protons, neutrons, and high-speed electrons, capable of causing ionisation
Types of radiant energy from long wavelength, low frequency to short wavelength, high frequency
- Radio waves
- Microwaves
- Infrared
- Visible light
- UV light
- X, gamma rays
- Cosmic rays
Alpha particles
2 protons, 2 neutrons
Beta particles
High speed positrons or electrons
High linear energy transfer
Particles which transmit large amounts of energy over short distances (eg alpha particles, high energy neutrons, beta
particles) produce severe but localised effects
Low linear energy transfer
- Characteristic of gamma and x- rays
- Penetrate deeply but interact with fewer molecules along the way.
Effects of ionising radiation on cells
- Very high doses: cell death due to irreparable DNA damage
- Lower doses: DNA synthesis interfered with
- Altered gene expression: p53 activation may result in cell cycle arrest, often apoptosis
- DNA synthesis without mitosis may produce cells with giant nuclei
- DNA damage may produce chromosomal abnormalities
-Reproductive death
Microscopic features of radiation injury
- Nuclear changes
- Cytoplasmic changes
- Vascular changes
- Fibrosis
Nuclear changes caused by radiation
- Nucleus is more sensitive than cytoplasm
- Swelling
- Chromatin clumping
- Micronuclei
- Apoptosis
Cytoplasmic changes caused by radiation
- Swelling
- Vacuolation,
- Membrane disruption
- Organelle disintegration
Vascular changes caused by radiation
- Early endothelial swelling
- Necrosis of wall with haemorrhage
- Later sclerosis → ischaemia
- Atrophy
Fibrosis
- Hallmark of radiation injury
- Stromal cells more resistant
- Often pleomorphic fibroblasts
Radiation injury
Acute vascular damage –> endothelial swelling, narrowing of lumen
Radiation injury in the bladder
- Chronic radiation cystitis
- Dense fibrosis
- Bizarre fibroblasts
Genetic effects of radiation on germ cells
- Chromosomal abnormalities (incompatible with life, may produce deformed babies)
- Point mutations (affect future generations)
- Sterility
Somatic effects of radiation
- May be acute or delayed
- Localised or affecting total body
Total body irradiation prodromal phase
- Anorexia
- Nausea and vomiting
- Dose dependent
Total body irradiation
asymptomatic latent phase
- Surviving cells function as normal until mitosis
- Dose dependent
Total body irradiation principle phase
- 1-3 successive syndromes
- Dose dependent
Syndromes of acute radiation sickness
- Haemopoietic
- Intestinal
- CNS
Haemopoietic syndrome
- Loss of stem cells in marrow
- No replacement of circulating cells.
- Thrombocytopenia, neutropenia, anaemia.
- Recovery by repair of non-lethal injury
Intestinal syndrome
- Damage to stem cells in crypts
- Epithelium denuded
- Loss of fluid, electrolytes
- Haemorrhage, septicaemia
- Regenerates within one week if possible
CNS syndrome
- Vascular effects: leakage and cerebral oedema
- No neuronal injury unless massive dose
Delayed somatic effects
- Carcinogenesis
- Abnormalities in growth and development (especially in foetus)
- Diminished life span
Radiation induced cancers
- Thyroid
- Leukemia
- Lung
- Breast
- Skin
- Angiosarcoma of liver
- Oesteogenic sarcome
Thorotrast exposure
- Radiographic medium used 1930-1945 that emits alpha particles
- Persists indefinitely in tissues
- Associated with angiosarcoma of liver
Effects of radiation in skin
- Early changes: Blistering, necrosis, hyper/hypopigmentation
- Chronic radiation damage: fibrosis, poor healing
- Later: Malignant tumours (squamous cell carcinoma)
Acute effects of radiation on lung
- Radiation pneumonitis
- DAD (diffuse alveolar damage)
Late effects of radiation on lung
- Impaired pulmonary function
- Interstitial fibrosis
- Carcinogenesis
Acute effects of radiation in bone marrow
Panhypoplasia
Chronic effects of radiation in bone marrow
Predisposition to acute and chronic myeloid leukaemia and acute lymphocytic leukaemia
Effects of radiation on kidney
Ischaemic vascular effects
Effects of radiation on gonads
Very susceptible, sterility common
