Medical Physics

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Part 2
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What can radiation do?
Death Cancer Skin Burns Cataract Infertility Genet
ic effects
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What can radiation do?
Deterministic effects death, skin burns,
cataract, infertility Stochastic
effects cancer, genetic effects
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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)

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OBJECTIVES OF RADIATION PROTECTION

• PREVENTION of deterministic effect.
• LIMITING the probability of stochastic effect

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Radiosensitivity RS

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

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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
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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.

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Who should be protected in Hospital?

• Patients.
• Members of his/her family.
• Workers.
• General public.

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Ionizing Radiation
We live with 1-3 mSv/y
Can kill 4000 mSv
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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

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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).

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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.

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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.

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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.

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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.

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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.

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Optimization principle ALARA
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OPTIMIZATION OFPATIENT EXAMINATION
Diagnostic objective Medical exposure
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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

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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

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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)

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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.

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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.

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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.

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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
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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
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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.
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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.
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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

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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.

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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??