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Medical Physics

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Part 8: Occupational exposure Part No 3, Lesson No 1 Biology IAEA Training Material: Radiation Protection in Radiotherapy * Part 1. Biological effects of ionizing ... – PowerPoint PPT presentation

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Title: Medical Physics


1
Part 2
2
What can radiation do?
Death Cancer Skin Burns Cataract Infertility Genet
ic effects
2
3
What can radiation do?
Deterministic effects death, skin burns,
cataract, infertility Stochastic
effects cancer, genetic effects
3
4
Early Observations of the Effects of Ionizing
Radiation
  • 1895 X Rays discovered by Roentgen
  • 1896 First skin burns reported
  • 1896 First use of X Rays in the treatment of
    cancer
  • 1896 Becquerel Discovery of radioactivity
  • 1897 First cases of skin damage reported
  • 1902 First report of X Ray induced cancer
  • 1911 First report of leukaemia in humans and
    lung cancer from occupational exposure
  • 1911 94 cases of tumour reported in Germany
    (50 being radiologists)

5
OBJECTIVES OF RADIATION PROTECTION
  • PREVENTION of deterministic effect.
  • LIMITING the probability of stochastic effect

5
6
Radiosensitivity RS
  • RS Probability of a cell, tissue or organ of
    suffering an effect per unit of dose.

7
RADIOSENSITIVITY
High RS Medium RS Low RS
Gonads Thyroid Eye lens Bone Marrow Spleen Lymphatic nodes Lymphocytes Skin Mesoderm organs (liver, heart, lungs) Muscle Bones Nervous system
8
Why do we need protection?
  • It is generally assumed that even very small
    doses of ionizing radiation can potentially be
    harmful .
  • Therefore, persons must be protected from
    ionizing radiation at all dose levels.

8
9
Who should be protected in Hospital?
  • Patients.
  • Members of his/her family.
  • Workers.
  • General public.

9
10
Ionizing Radiation
We live with 1-3 mSv/y
Can kill 4000 mSv
10
11
Patients Protection
  • Persons are medically exposed as part of their
    diagnostic or treatment
  • According to IAEA, ICRP and BSS, two basic
    principles of radiation protection are to be
    complied with
  • justification and optimization

12
RP Principles vs. Actions
  • Justification
  • Optimization
  • Dose Limitations
  • Time
  • (dose directly proportional to length of
    exposure).
  • Shielding
  • (b/w source and patient).
  • Distance
  • (Intensity and StP distance).

13
Justification
  • No use of ionizing radiation is justified if
    there is no benefit.
  • All applications must be justified.
  • This implies All, even the smallest exposures
    are potentially harmful and the risk must be
    offset by a benefit.

13
14
The justification of a practice
  • The decision to adopt or continue any human
    activity involves a review of benefits and
    disadvantages of the possible options
  • E.g. choosing between the use of X Rays or
    ultrasound
  • Most of the assessments needed for the
    justification of a practice are made on the basis
    of experience, professional judgement, and common
    sense.

15
Risk/Benefit analysis
  • Need to evaluate the benefits of radiation - an
    easy task in the case of nuclear medicine.
  • Radiation is the diagnostic and therapeutic
    agent.
  • Assessment of the risks requires the knowledge of
    the dose received by persons.

15
16
Optimization
  • When radiation is to be used then the exposure
    should be optimized to minimize any possibility
    of detriment.
  • Optimization is doing the best you can under the
    prevailing conditions.
  • Need to be familiar with techniques and options
    to optimize the application of ionizing radiation
    - this is really the main objective of the
    present course.

16
17
Optimization
  • Reducing the patient dose may reduce the quantity
    as well as the quality of the information
    provided by the examination or may require
    important extra resources.
  • Means that doses should be As Low As Reasonably
    Achievable ALARA, economic and social factors
    being taken into account compatible with
    achieving the required objective.

18
Optimization principle ALARA
18
19
OPTIMIZATION OFPATIENT EXAMINATION
Diagnostic objective Medical exposure
20
Optimization of image quality
  • Image quality depends on
  • Administered activity
  • Technical factors - equipment used -
    acquisition protocol - image processing
    evaluation - noise - spatial resolution
  • - scatter
  • Patient factors - size
  • - age
  • - disease - movement

21
Framework of RP for medical exposure
  • Justification
  • Optimization
  • The use of doses limits is NOT APPLICABLE
  • Dose constraints and guidance (or reference)
    levels ARE RECOMMENDED

22
Three types of exposure
  • Medical Exposure (principally the exposure of
    persons as part of their diagnostic or treatment)
  • Occupational Exposure (exposure incurred at work,
    and practically as a result of work)
  • Public Exposure (including all other exposures)

23
Medical exposure
  • Medical Exposure
  • Exposure of persons as part of their diagnostic
    or treatment.
  • Exposures incurred by volunteers as part of a
    program of biomedical research.

24
Responsibilities for Medical Exposure
  • (a) No patient to be administered a diagnostic
    or therapeutic medical exposure unless the
    exposure is prescribed by a medical
    practitioner
  • (d) For therapeutic uses of radiation, the
    calibration, dosimetry and quality assurance
    requirements of the Standards be conducted by or
    under the supervision of a qualified expert in
    radiotherapy physics.

24
25
PUBLIC
  • effective dose of 1 mSv/year
  • equivalent dose to lens of the eye 15 mSv/yr
  • equivalent dose to skin of 50 mSv/year.

26
Guidance levels for diagnostic radiography
(typical adult patient)
Examination Entrance surface dose per radiograph (mGy)
Lumbar spine AP 10
Lumbar spine LAT 30
Lumbar spine LSJ 40
Abdomen, IVU and cholecystography AP 10
27
Guidance levels for diagnostic radiography
(typical adult patient)
Examination Entrance surface dose per radiograph (mGy)
Pelvis AP 10
Hip joint AP 10
Chest PA 0.4
Chest LAT 1.5
28
Typical effective doses from diagnostic medical
exposures
Diagnostic procedure Typical effective dose (mSv) Equiv. no. of chest x-rays Approx. equiv. period of natural background radiation
Chest (single PA film) 0.02 1 3 days
Skull 0.07 3.5 11 days
Thoracic spine 0.7 35 4 months
Lumbar spine 1.3 65 7 months
From Referral Criteria For Imaging. CE, 2000.
29
Typical effective doses from diagnostic medical
exposures
Diagnostic procedure Typical effective dose (mSv) Equiv. no. of chest x-rays Approx. equiv. period of natural background radiation
CT head 2.3 115 1 year
CT chest 8 400 3.6 years
CT Abdomen or pelvis 10 500 4.5 years
From Referral Criteria For Imaging. CE, 2000.
30
OCCUPATIONAL - APPENDIX I
  • Dose Limits
  • effective dose of 5mSv per year averaged over
    five consecutive years
  • equivalent dose to lens of eye of 150mSv in a
    year
  • equivalent dose to extremities or skin of 500mSv
    in a year.
  • For apprentices (16-18 years of age)
  • effective dose of 6mSv in a year

30
31
OCCUPATIONAL
  • Female workers should notify pregnancy.
  • Working conditions shall be adapted to ensure
    that the embryo and fetus are afforded the same
    broad level of protection as for members of the
    public.

31
32
Class Activity 3
  • Mr. Sharp, I am given to understand that 2 bone
    scans and a cardiac study done on me have given
    me 22 mSv whereas 20 mSv is the safe dose. I want
    to file legal suit against the doctor. What do
    you feel??
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