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