Acute Radiation Syndrome

MUDr. Michal Jurajda, PhD.

The scope of the training

• Radiobiology basics

• Hematopoietic syndrome in animal as the example of radiation damage

• Statistical evaluation of data

Ionizing radiation

• Energetic particles or Electromagnetic waves. It comprises a wide part of electromagnetic spectrum ranging from gamma rays to short wavelength UV. Radiation energy above the ultraviolet range is called ionizing radiation because the photons have enough energy to knock electrons off atoms and break molecules.

Ionizing radiation

• Ionizing of molecules and atoms within the cells:– by direct hitting the target molecules (direct

effects of ionization)– by producing free radicals that interact with

critical cell components (indirect effects).

• Cell response: swelling, disruption of mitochondria, alterations in cell membrane, changes in the nucleus

Stochastic and deterministic effect of

radiation

• Definiton

• Differences

• Examples

Ionizing radiation – stochastic effects

• Effects well documented in atomic bomb survivors

• Between 1950 and 1970, the death rate from leukemia alone in the most heavily exposed population groups of the atomic bomb survivors in Hiroshima and Nagasaki was 147/100000, 30 times the expected rate

• Type of cancer that develops depends on the dose of radiation, the sex of the person, age at which exposure occured

• Children exposed to ionizing radiation in utero have an increased risk for developing leukemias and childhood tumors, particularly 2-3 years after birth. This latency periond for leukemia extends to 5 to 10 years for certain solid tumours (35 years for thyroid cancer)

Sources of radiation

• Natural– Cosmic radiation– Radioactive substances

• Man made– Particle Accelerators– X-rays tubes

Half-time

• Half-life is the time required for the activity of a radioactive material to be reduced to one-half its original value

Interaction of Ionizing Radiation with Matter

• Photoelectric effect

• Compton effect

• Formation of electron-positron couples

Protection against radiation

• Effect of time – Fractionition

• Effect of distance

• Effect of shielding

Radiation effect on living subjects

• Direct effectDirect effect= direct destruction of biomolecules

• Indirect effectIndirect effect= free radicals formation via radiolysis of water

• Cell recovery

• Correlation between dosis and effect

Sensibility of living systems

• Proliferation kinetics of tissue– Irreversibly postmitotic organs– Intermitotic and premitotic tissues

• Number of cells in proliferation– Every dosis of radiation leads to decrease in

number of cells which is proportional to growth fraction

Radiosensitivity alteration

• Oxygen effect

• Dosis fractionation

• Alkylation cytostatics

• Hypertermia– Hypotermia (protective effect)

Radiation responsiveness

• Manner in which a radiosenstive tissue Manner in which a radiosenstive tissue responds to irradiationresponds to irradiation

• One of the major determinants of radiation responsiveness is tissue oxygenation (O2 is a rich source of free radicals that form and destroy essential cell components during irradiation

• Hypoxic cells are more radioresistant (radiosensitisers are being investigated)

Deterministic effects of Deterministic effects of radiationradiation

Acute radiation syndromeAcute radiation syndrome

• Hematopoietic syndrome (bone marrow syndrome)

• Gastrointestinal syndrome

• Cardiovaskular/ CNS syndrome

HormesisHormesis

• Not accepted !!!!

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Výška = 0,1 mm