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Radiation Protection in Radiotherapy

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Title: Radiation Protection in Radiotherapy


1
Radiation Protection inRadiotherapy
IAEA Training Material on Radiation Protection in
Radiotherapy
  • Part 4
  • Principles of Radiation Protection

2
The two aims of radiation protection
  • 1. Prevention of deterministic effects (except in
    radiotherapy those that are intentionally
    produced, but including those which are NOT
    intended, such as accidental medical exposure)
  • 2. Reduction of the probability of stochastic
    effects

3
Deterministic effects
  • Due to cell killing
  • Have a dose threshold - typically several Gy
  • Specific to particular tissues
  • Severity of harm is dose dependent

4
Stochastic effects
Probability of effect
  • Due to cell changes (DNA) and proliferation
    towards a malignant disease
  • Severity (example cancer) independent of the dose
  • No dose threshold - applicable also to very small
    doses
  • Probability of effect increases with dose

dose
5
The need for protection applies to all dose levels
  • It is generally assumed that even very small
    doses of ionizing radiation can potentially be
    harmful (linear no threshold hypothesis)
  • Therefore, persons must be protected from
    ionizing radiation at all dose levels

6
Objectives
  • Appreciate the need for radiation protection
  • Be familiar with the recommendations of the ICRP
    and the requirements of the IAEA BSS
  • Appreciate the fundamental principles of
    justification, optimization and dose limitation
    in radiological protection
  • Understand the importance of the BSS in the
    context of radiation protection in radiotherapy

7
Contents
  • Lecture 1 Basic Principles of Radiation
    Protection
  • Lecture 2 The Basic Safety Standards (BSS) of
    the IAEA (1996)

8
Radiation Protection inRadiotherapy
IAEA Training Material Radiation Protection in
Radiotherapy
  • Part 4
  • Principles of Radiation Protection
  • Lecture 1 General Principles

9
Objectives
  • Appreciate the need for radiation protection
  • Be familiar with the recommendations of the ICRP
  • Appreciate the fundamental principles of
    justification, optimization and dose constraints
  • Be able to apply very basic radiation protection
    principles to the radiotherapy environment

10
Contents
  • 1. The ICRP recommendations
  • 2. Basic principles
  • Justification
  • Optimization
  • Dose limitation
  • 3. Time, distance, shielding

11
The International Commission on Radiological
Protection
  • A group of recognized leaders in the field of
    radiation protection
  • established 1928 (by the International Congress
    of Radiology ICR)
  • concerned with the protection of humans from
    ionizing radiation
  • official relationships with WHO, IAEA, ICRU
  • convenes task groups of experts to address
    particular issues
  • issues reports and recommendations

12
Recommendations of the ICRP
  • Prepared typically by a task group which includes
    other experts
  • Approved by the full commission
  • Published in the journal Annals of the ICRP
  • Have no legislative mandate themselves - however,
    are typically the foundation onto which national
    legislation is built

13
Important ICRP reports for the present course
  • ICRP. Protection against ionising radiation
    from external sources used in medicine, ICRP
    report 33. Oxford Pergamon Press 1982.
  • ICRP. Protection of the patient in
    radiotherapy, ICRP report 44. Oxford Pergamon
    Press 1985.
  • ICRP. Radiological Protection and Safety in
    Medicine, ICRP report 73. Oxford Pergamon Press
    1996.
  • ICRP. Radiological Protection and Safety and
    pregnancy, ICRP report 73. Oxford Pergamon
    Press 1996.
  • ICRP. Protection from potential exposures
    application to selected radiation sources, ICRP
    report 76. Oxford Pergamon Press 1997.
  • ICRP. Prevention of accidental exposures to
    patients undergoing radiation therapy, ICRP
    report 86. Oxford Pergamon Press 2002.

14
Essential reading
  • ICRP. The 1990 recommendations of the
    International Commission on Radiological
    Protection, ICRP report 60. Oxford Pergamon
    Press 1991.

15
The ICRP Recommendations
  • ICRP publication 60 - 1990
  • The recommended system of radiation protection is
    based upon 3 principles
  • Benefit of a practice must offset the radiation
    detriment
  • Exposures and likelihood of exposure should be
    kept as low as reasonably achievable, economic
    and social factors being taken into account
  • Dose limits should be set to ensure that no
    individual faces an unacceptable risk in normal
    circumstances

16
ICRP 60
  • Weighs all existing data to arrive at
    quantitative recommendations for risk, detriment,
    dose and dose rate weighting factors
  • Considers exposure to humans only
  • Considers exposure in three categories
    occupational, medical, public

17
IAEA BSS (1996) - glossary
  • Occupational exposure
  • All exposures of workers incurred in the course
    of their work, with the exception of exposures
    excluded from the Standards and exposures from
    practices or sources exempted by the Standards.

18
IAEA BSS (1996) - glossary
  • Medical exposure
  • Exposure incurred by patients as part of their
    own medical or dental diagnosis or treatment by
    persons, other than those occupationally exposed,
    knowingly while voluntarily helping in the
    support and comfort of patients and by
    volunteers in a programme of biomedical research
    involving their exposure.

19
IAEA BSS (1996) - glossary
  • Public exposure
  • Exposure incurred by members of the public from
    radiation sources, excluding any occupational or
    medical exposure and the normal local natural
    background radiation but including exposure from
    authorized sources and practices and from
    intervention situations.

20
2. Fundamental principles of radiation protection
  • Justification of practices
  • Limitation of doses
  • Optimization of protection and safety

21
2. Fundamental principles of radiation protection
  • Justification of practices
  • Limitation of doses
  • Optimization of protection and safety
  • no dose limitation applies to medical exposure
    - however, both justification and optimization
    are essential

22
Time for Discussion
Justification
Optimization
  • What do the three principles imply to you?

Dose limitation
23
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

24
Risk/Benefit analysis
  • Need to evaluate the benefits of radiation - an
    easy task in the case of radiotherapy
  • Radiation is the therapeutic agent
  • Assessment of the risks requires the knowledge of
    the dose received by persons

25
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

26
Optimization in the context of radiotherapy
  • Two aspects
  • Optimization of the dose to the target
    MAXIMIZATION of dose
  • Optimization of protection
  • of the staff (part 8 of the present course)
  • of the patient (parts 9 to 13)
  • of the public (part 17)
  • Only the second aspect is objective of radiation
    protection

27
A comment on the optimization of patient
protection
  • Optimization of treatment is primary objective of
    radiotherapy
  • This includes
  • optimizing the dose distribution to the target
  • reduction of possibility of severe side effects
    by minimizing the dose to other structures
  • accident prevention

28
Optimization
  • Must take into account the resources available -
    this includes economic circumstances
  • Often a tricky question - where shall we stop,
    how much shielding should we really use?

29
Optimization principle
30
very much in line with the rest of real life
  • Both justification and optimization are part of
    all strategies when handling potentially harmful
    substances or dealing with risks
  • there must be a benefit
  • the risk should be kept as low as possible
  • Same for household chemicals, drugs, traffic,
    travel, sports, .

31
A comment on optimization (as low as reasonably
achievable)
  • Issues which are often subject of discussion
  • L what is a low dose?
  • R what is reasonable?

32
What is low?
  • It can be very costly to consider every dose
    level explicitly
  • Discussions are on-going about dose levels below
    regulatory concern
  • A potential starting point are doses from natural
    background which are inevitable and one can
    assume organisms have adapted to them

33
Contributions to Radiation Exposure in the UK
Total 2-3mSv/year
34
Average annual doses in mSv from natural sources
in European countries
35
What is Radon (222Rn) ?
  • It is a radioactive gas that exists everywhere in
    the atmosphere
  • It is a member of the 238U series
  • It is formed by the decay of 226Ra

36
What is Radon (222Rn) ?
  • Half-life 3.82 days
  • It is an alpha emitter decaying to 218Po
  • 218Po is also an alpha emitter (T½ 3 min)
  • Other important decay products are 214Po (a, T½
    0.164 msec) and 214Bi (b, T½ 19.9 min)

37
Why is Radon a Problem?
  • The hazard arises from the inhalation of its
    decay products which are not gaseous
  • Most of the decay products become attached to
    aerosols in the atmosphere and are deposited in
    the conducting airways and in the lung during
    respiration.

38
Other important contributions to natural
exposure Potassium-40
  • 40K constitutes 120 parts per million of stable
    potassium which is an essential trace element in
    every human body
  • 40K has a half-life of 1.28 x 109 years, decaying
    by beta emission (Emax 1.3 MeV)
  • An 80 kg adult male contains about 180 g of
    potassium -gt 18 mg of 40K
  • This gives an annual internal effective dose of
    170 µSv

39
The cosmic ray contribution to the background
radiation varies markedly with altitude. Note,
that at cruising altitude in a Boeing 747 the
dose rate is approximately 5 mSv/h
40
Average Background DosesUNSCEAR 2000 Report
  • WORLDWIDE AVERAGE DOSES
  • Source
    Effective dose Typical range

  • (mSv per year)
    (mSv per year)

  • External exposure
  • Cosmic rays 0.4 0.3-1.0
  • Terrestrial gamma rays
    0.5 0.3-0.6
  • Internal exposure
  • Inhalation 1.2 0.2-10
  • Ingestion 0.3 0.2-0.8
  • Total 2.4 110

41
What is reasonable?
  • Depends on prevailing conditions including
  • economic
  • cultural
  • May be different for different individuals,
    however the risk/benefit analysis made in parts 3
    and 6 of the course provides a rational basis

42
Average Annual Risk of Death in the UK from
Industrial Accidents and from Cancers due to
Radiation Work
From L Collins 2000
43
Dose limitation
  • No dose limitation for medical exposure of the
    patient - it is always assumed that the benefits
    for the patient outweigh the risks
  • Limits need to be applied for public and
    occupational exposures.

44
Limits and constraints
  • Dose limits are one of the three principles of
    protection as introduced by ICRP and BSS. Fixed
    dose limits are recommended by ICRP and often
    enforced by a national legal process (Radiation
    Protection Legislation).
  • Dose constraints are used in an optimization
    process to guide planning. Constraints and the
    importance thereof may be subject to change to
    achieve the optimum solution to a problem (Best
    practice guidelines).

45
Optimization and dose limitation
  • It is NOT the aim to get close to the limit
    values - the aim is to get as low as reasonably
    achievable
  • Is part of risk management
  • Keeps the risks of dealing with ionizing
    radiation of the same order as other risks

46
If radiation is justified, how do we optimize the
exposure and do not exceed dose limits?
  • this is the objective of practical radiation
    protection

47
3. Basic radiation protection strategies
  • Radiation cannot be seen, heard or felt.
    Therefore it is essential to know about it.
  • Can be accurately measured using appropriate
    instruments
  • Need appropriately qualified expert

Smart Ion from Mini-Instruments
48
Basic radiation protection strategies
  • Radiation cannot be seen, heard or felt.
    Therefore it is essential to know about it.
  • Need signs and interlocks

49
Basic radiation protection strategies
  • Hazard Reduction Methods
  • Time
  • Distance
  • Shielding

50
Time
Dose is proportional to the time exposed
Dose Dose-rate x Time
51
Consequence
  • Reduce time in contact with radiation sources as
    much as compatible with the task
  • Training of a particular task using
    non-radioactive dummy sources helps

52
Distance
  • Inverse square law (ISL)

Dose-rate ? 1/(distance)2
53
Inverse square law ISL
54
Example from brachytherapy
55
Consequence
  • Distance is very efficient for radiation
    protection as the dose falls off in square
    (compare also part 2 of the course)
  • Examples
  • long tweezers for handling of sources
  • big bunkers for radiation equipment

56
Shielding
Barrier thickness
incident radiation
transmitted radiation
57
Shielding
  • Easy to do during construction
  • Typically thick shielding required in
    radiotherapy which cannot be incorporated in
    personal protective equipment
  • More details in part 7 of the course

58
Summary I
  • Humans must be protected from ionizing radiation
    at all dose levels
  • Exposure can occur in three different categories
  • Occupational
  • Medical
  • Public

59
Summary II
  • The basic principles of a system of radiation
    protection are
  • Justification of practices
  • Dose limits to individuals
  • Optimization of protection
  • Even simple measures such as reducing the time
    exposed to irradiation or keeping distance can be
    effective measures to reduce exposure

60
Any questions?
61
Question
  • Please discuss the differences between external
    and internal exposures and the implications for
    radiation safety

62
Radiation Exposure
Internal
External
63
External Exposure
64
Internal Exposure
65
Acknowledgment
  • Pedro Ortiz López, IAEA
  • Lee Collins, Westmead Hospital
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