Acute Radiation Syndrome Revision MRD441 PDF

FINAL EXAM ​L5: Acute Radiation Syndrome ARS (Acute Radiation Syndrome) or radiation sickness occurs in humans after whole-body reception of large doses of ionizing radiation delivered over a short period of time. Human populations exposed to doses of ionizing radiation sufficient to cause ac...

FINAL EXAM ​L5: Acute Radiation Syndrome ARS (Acute Radiation Syndrome) or radiation sickness occurs in humans after whole-body reception of large doses of ionizing radiation delivered over a short period of time. Human populations exposed to doses of ionizing radiation sufficient to cause acute radiation syndrome have been obtained from: Early radiation responses are described as deterministic. -​ Deterministic radiation responses are those that inhibit increasing severity with increasing radiation dose. Four major response stages of Acute Radiation Syndrome: Prodromal Stage Latent period Manifest illness Repair and (hours or a few Recovery days) Occurs within hours Occurs for about 1 The period when Occur when cells after whole-body week, during which symptoms that are exposed to absorbed dose of no visible symptoms affect: sublethal doses of 1Gy or more. occur. 1.​ Hematopoietic ionizing radiation. 2.​ Gastrointestinal After irradiation, 3.​ Cerebrovascular surviving cells begin systems become to repopulate.  visible Human cells contain a repair mechanism inherent in their biochemistry. The severity of the In severe high-dose symptoms depend cases, emaciated on the dose related: (weak) human -​ The higher the beings eventually dose, the more die. severe the symptoms. The surviving cells can repopulate show that the organ has regain some functional ability. However, the amount of functional damage sustained determines the organ’s potential for recovery. -​ Oxygenated cells receive dose of Low-LET radiation, the severely damaged is more. And those that survive repair and recover from the injury -​ Hypoxic cell (less oxygen) is less severely damaged, do not repair and recover efficiently. Acute Radiation Syndrome is a collection of symptoms associated with high-level radiation exposure. Three separate dose-related syndromes occur as part of total-body syndrome: Syndrome Dose Prodromal Latent Stage Manifest Illness Recovery Stage Stage Hematopoietic 2.5-5 Gy Symptoms Stem cells in Symptoms are: In most cases, (bone marrow (250-500ra (onset 1H to 2D bone marrow -​ Anorexia bone marrow syndrome) ds) after exposure) die -​ Fever cells will begin to The most are: -​ Malaise repopulate the -​ Anorexia This stage radiosensitive marrow. -​ Nausea lasts 1-6 ​Drop in blood cell -​ Vomiting weeks counts for several There should be weeks full recovery for a This stage lasts ​Survival large percentage for minutes to decreases as dose of individuals days increases from a few weeks ​Most deaths up to two years occurs within 1-2 after exposure months after The LD50/60 is exposure about 2.5 to) 5 Gy (250 to 500 rads. Gastrointestina > 10 Gy Symptoms are: Stem cells in Symptoms are The LD100 is l (5-12 Gy) -​ anorexia bone marrow malaise, anorexia, about 10 Gy -​ severe and cells lining severe diarrhoea, (1000 rads). nausea GI tract are fever, dehydration, -​ vomiting, dying, although and electrolyte -​ cramps patient may imbalance. -​ diarrhoea. appear and Death is due to Onset occurs feel well. infection, within a few Stage lasts dehydration, hours after less than 1 exposure. week. Stage lasts about 2 days. Cerebrovascul 100Gy Symptoms are Patient may Symptoms are return No recovery is ar Total body extreme return to partial of watery diarrhoea, expected. dose of nervousness functionality. convulsions, and X-Rays or and confusion; Stage may coma. total severe nausea, last for hours Onset occurs Neurons vomiting, and but often is 5 to 6 hours watery less. after exposure. diarrhoea; loss Death occurs within of 24-48 hours of consciousness; exposure. and burning sensations of the skin. Onset occurs within minutes of exposure  ​L6: Cells Radiosensitivity (Law of Bergonie and Tribondeau) ​L7: Principle of Radiation Protection 1.​ What is radiation protection -​ A series of actions or measures that need to be taken in order to reduce the risks of radiation injury to patient, personnel and public. 2.​ Objective of radiation protection -​ To prevent the occurrence of deterministic effects by keeping doses below relevant thresholds, and to ensure that all reasonable steps are taken to reduce the induction of stochastic effects. -​ To prevent the occurrence of serious radiation-induced conditions in exposed persons and to reduce stochastic effects in exposed persons to a degree acceptable in relation to the benefits to the individual and to society from the activities that generate such exposure. 3.​ Principles of radiation Principles of radiation Explanation  Justification Optimization -​ ALARA -​ Takes into consideration of social and economic factor -​ How to achieve optimization in radiation protection a)​ Proper education and training b)​ Follow guidelines and recommendation by authorities -​ Radiographers should understand the factors that affect dose, dose reduction methods, and shielding requirements. Limitation of the doses -​ To ensure that no individual is exposed to radiation risks that are judged to be unacceptable from radiological practices in any normal circumstances -​ Deals with the establishing annual dose limits for occupational exposures, public exposures and exposures to embryo and fetus -​ DO NOT include medical exposures and natural background radiation. ​L8: Radiation Effects to embryo and fetus ​L9: Equipment Specifications 9.1 Equipment to control distance 9.2 Shielding 9.3 Rooms 9.4 Radiation in CT suite -​ CT contributes up to 40% of the collective dose from diagnostic radiology. -​ The dose unit used in CT is the computed dose index CTDI. -​ CTDI air - terms of absorbed dose to air. -​ Coefficient of Dtissue and Dair is 1.06 and error is not greater than ±1%. a)​ This measurements are made using a special pencil ionisation chamber or a thermoluminescent dosimeter (TLD). -​ Scattered radiation and radiation documented on the floor of the CT suite could be as high as 0.3 Gy/day. 9.5 Radiation Protection in CT suite -​ Shielding: Adequate shielding should be provided for the floor and roof areas of a CT suite -​ Wall: Additional thickness of 2.5mm of lead or 162mm of concrete to shield the front and rear reference point, so as to reduce the dose to 1 mGy/year. -​ Collimation: highly collimated x-ray beam in CT results in markedly non uniform distribution of absorbed dose perpendicular to the tomographic plane during the CT exposure. -​ Gantry size: the size of the CT room housing the gantry of the CT unit as recommended by AERB should be less than 25m2 ​L10: Radiation Monitoring 10.1: Monitoring Instrument  1.​ Types of Monitoring: a)​ Personnel Monitoring - to control occupational exposure of working personnel b)​ Workplace and Environmental Monitoring - to control public exposure 2.​ The factors that depends on the selection of a specific measuring device: a)​ Relative intensity of the radiation b)​ Required measurement accuracy 3.​ Here are the types of monitoring devices and what are the device measure: Measurement Device Xray beam exposure Ionization Chamber Environmental exposure Survey meters Personnel exposure 1.​ Film badge 2.​ Thermoluminescent Dosimeters (TLD) Radioactivity 1.​ Scintillation detectors 2.​ Activity calibrators 4.​ Types of Radiation Detector: Types of Elaboration Monitoring Detectors 1.​ Gas-filled -​ Used for charged particles producing ionization in gas filled chamber  -​ Main differences between these three types of gas-filled detectors are: a)​ Gas used b)​ Pressure at which the gas is maintained within the chamber c)​ Voltage level that is maintained between the central electrode and walls of the chamber. 2.​ Scintillatio -​ Made up of sodium iodide thallium-activated detector, NaI(TI). n -​ Measures the light released by a crystal after an interaction with radiation. -​ Consists of: a)​ Single crystal, NaI(TI), anthracene b)​ Photomultiplier tubes (PMT) 3.​ Solid State -​ Maximize ionizing radiation capture (semicond  uctors) -​ Types of solid state detectors: a)​ Silicon detector - high-resistivity Di substrates cause extremely low noise, low-leakage-current fabrication process b)​ Germanium detector - excellent energy resolution, potentially high spatial resolution, large active volumes (result high detector efficiencies), simplified fabrication, enabling unique detector geometries and detection schemes. -​ Advantages and disadvantages Advantages Disadvantages 1.​ Long life expectancy 1.​ Lower sensitivity 2.​ Improved reliability (the readings 2.​ Poor energy resolution, more stable than other detector) scatter rejection 3.​ Improved maintainability 3.​ Poor spectral performance (semiconductor detectors operate 4.​ Voltage supplied must large at a fixed) enough 4.​ Low voltage (the need for work in 5.​ Too high energy photon adjusting the detectors is greatly reduced) a)​ Miniaturization b)​ Compact design 10.2: Types of Personal Radiation Monitoring Devices