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RA 221 – RADIATION BIOLOGY

RA 221 – RADIATION BIOLOGY. PROTECTION METHODS PATIENTS & PERSONNEL. CARDINAL PRINCIPLES. TIME DISTANCE SHIELDING. ALARA CONCEPT. KEEP EXPOSURES A S L OW A S R EASONABLY A CHIEVABLE OCCUPATIONAL EXPOSURE SHOULD NEVER BE GREATER THAN 10% OF EDL

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RA 221 – RADIATION BIOLOGY

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  1. RA 221 – RADIATION BIOLOGY PROTECTION METHODS PATIENTS & PERSONNEL

  2. CARDINAL PRINCIPLES • TIME • DISTANCE • SHIELDING

  3. ALARA CONCEPT • KEEP EXPOSURES AS LOW AS REASONABLY ACHIEVABLE • OCCUPATIONAL EXPOSURE SHOULD NEVER BE GREATER THAN 10% OF EDL • SHOULD GENERALLY NOT EXCEED 1mSv/year (100 mrem/year)

  4. PATIENT EXPOSURE • MEASURING PATIENT EXPOSURE • ESE – ENTRANCE SKIN EXPOSURE • Measurement (actual vs nomogram) • MEAN MARROW DOSE • Measurement based on amount of bone marrow exposed • GONADAL DOSE • Average dose to gonads based on exposure proximity • GENETICALLY SIGNIFIGANT DOSE

  5. CURRENT HUMAN EXPOSURE LEVELS

  6. OCCUPATIONALEXPOSURE LIMITS • HISTORICAL LIMITS • P 617, Table 40-3 • CURRENT NCRP LIMITS • P 619, Table 40-4

  7. AREA MONITORING • Purpose: To detect and measure radiation with survey instruments • All detect ionization in air • Ionization chambers • Proportional counters • Geiger-Muller

  8. AREA MONITORING

  9. PERSONNEL MONITORING • Measures radiation received by OCCUPATIONAL WORKERS • Required if potential exposure equals at least 25% of equiv. Dose limit

  10. PERSONNEL DOSIMETER • BASIC REQUIREMENTS: • Easy to carry and use • Durable • Reliable • Interaction with ionizing radiation similar to human tissue reaction

  11. APPROPRIATE DOSIMETER USE • To record exposure to wearer’s trunk • Non-fluoro – at waist or chest level • Fluoro – at collar, outside apron • Dual monitoring • Pregnant workers = collar and waist • Fluoro policy = collar and waist

  12. Lightweight Easy to handle Durable Not significantly affected by outside influences Able to detect & record small to large exposures Perform consistently and reliably Cost effective PERSONNEL DOSIMETERSMUST BE

  13. TYPES OF DOSIMETERS • FILM BADGE • TLD • POCKET IONIZATION CHAMBERS

  14. FILM BADGE • X-RAY FILM IN AN ENVELOPE • SENSITIVE ENOUGH TO DISTINGUISH BETWEEN PRIMARY AND SCATTER RADIATION • CONTROL BADGE REQUIRED FOR COMPARISON

  15. FILM BADGE: ADVANTAGES • Reasonably accurate • Permanent record • Durable / not easily damaged • Cost effective

  16. FILM BADGE: DISADVANTAGES • Temperature & humidity sensitive • One month maximum wear time • Accuracy decreases at keV ranges below 10 mR • Below 10mR recorded as (M) minimal

  17. THERMOLUMINESCENT DOSIMETER - TLD • Primary component = lithium fluoride crystals • Crystals store energy • Conversion of stored energy to visible light • Amount of light indicates exposure

  18. TLD: ADVANTAGES • Very accurate • Detects exposure values as low as 5mR • Not temp. and humidity sensitive • Can be used for up to 3 mos. without reading • Reusable – up to 1 year

  19. TLD: DISADVANTAGES Expensive – BUT replacement is less often Exposures must be recorded and maintained by institution – no permanent record

  20. OPTICALLY STIMULATED DEVICE (OSL) • Aluminum oxide as radiation detector • Radiation stimulates electrons • Laser light applied, returning electrons to normal state • Causes emission of light in proportion to radiation received

  21. ADVANTAGE OF OSL • Minimum reportable dose of 1mrad • More accurate - + or – 1mrad

  22. REPEATS TECHNIQUE IMAGE RECEPTOR FLUORO PT. POSITIONING PA vs AP GONADAL SHIELDING When used? When not used? Other types of shielding? COMMUNICATION IMMOBILIZATION TUBE FILTRATION NCRP requirements UNNECESSARY EXAMS PROCESSING DIGITAL IMAGING Preventing over exposure Others? DECREASING PATIENT EXPOSURE

  23. DECREASING PERSONNEL EXPOSURE • FLUORO • PORTABLES • DIAGNOSTIC BARRIERS • Permanent barriers • Control panel barrier is never a primary • SHIELDING • Stand at 90o to beam & scattering object • Scatter = 0.1% of beam intensity at 90o • OTHERS?

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