radiation protection - medicinsk strålningsfysik, lund · icrp publication 103 » the 2007...
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Radiation protectionCRISTER CEBERG
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International standards in RP
» International Commission on Radiological Protection (ICRP)
» International Atomic Energy Agency (IAEA)
» The European Union (EU)
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Science, Philosophy, and Regulations
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The scientific basis
• UNSCEAR: United Nations Scientific Committee on
the effects of Atomic Radiation
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The scientific basis
• UNSCEAR: United Nations Scientific Committee on
the effects of Atomic Radiation
• BEIR: Biological Effects of Ionizing Radiation
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The scientific basis
• UNSCEAR: United Nations Scientific Committee on
the effects of Atomic Radiation
• BEIR: Biological Effects of Inonizing Radiation
• REFR: Radiation Effects Research Foundation
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Philosophy and policy
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The objective of ICRP
The objective of the work of ICRP is to contribute to an appropriate
level of protection against the detrimental effects of ionising
radiation exposure without unduly limiting the benefits associated
with the use of radiation.
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ICRP
» UK registered charity
» Chair: Dr Claire Cousins
» 125 publications
» Financed by organisations
with interest in radiological protection
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The General Structure of ICRP
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ICRP Publication 103
» The 2007 Recommendations of
the International Commission on
Radiological Protection
» Approved by the Commission in
March 2007
» Most recent description of the
overall system of radiological
protection
Annals of the ICRP
ICRP Publication 103
Volume 37. No. 2-4 2007.
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The general purpose
» The general purposes of radiological protection are to:
– prevent detrimental deterministic effects such as
erythema, cataract, etc.
– limit the probability of stochastic effects, such as
cancer and hereditary effects, to levels deemed to be
acceptable
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We live with
1-3 mSv/y
Is there a safe point?
If not, how to deal with the problem?
Based on scientific data
Can kill
4000 mSv
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» The ICRP system is based upon 3 principles:
– Justification: Any decision that alters the radiation exposure situation should do more good than harm
– Optimisation: The likelihood of incurring exposure, the number of people exposed, and the magnitude of their individual doses should all be kept As Low As Reasonably Achievable, taking into account economic and societal factors
– Dose limits: The total dose to any individual from regulated sources should not exceed the appropriate limits (specified by ICRP)
The ICRP system
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» ICRP has a situation-based approach applying the fundamental principles to all conceivable exposure situations:
– Planned exposure situation
– Emergency exposure situation
– Existing exposure situation
The ICRP system
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» The Commission distinguishes between three categories of exposures:
– Occupational exposure
– Public exposure
– Medical exposure (patients)
The ICRP system
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ICRP policies are used worldwide
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Regulatory practicalities
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The United Nations system
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The International Atomic Energy Agency
» Verifying the peaceful uses of atomic energy
» Promoting safety
» Enabling the transfer of technology
» Establishing standards of safety and to provide for their application
» Facilitating the establishment of conventions
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IAEA RADIATION SAFETY
FUNCTIONS
Article III.A.6 of its Statute
To establish standards of
radiation safetyTo provide for the application of
these standards
To service
international
conventions
IAEA Safety Standards
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IAEA Safety Standards
» Safety Fundamentals
– Fundamental Safety Principles (SF-1)
» General Safety Requirements
– e.g. Radiation Protection and Safety of Radiation Sources:
International Basic Safety Standards (GSR Part 3)
» General Safety Guides
– e.g. Assessment of Occupational Exposure Due to External
Sources of Radiation (RS-G-1.3)
» Safety Report Series
– e.g. Radiation Protection in the Design of Radiotherapy
Facilities (No. 47)
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» First Basic Safety Standards 1962
» Revised Basic Safety Standards 1967
» Revised and Joint with FAO, ILO, OECD/NEA, WHO 1982
» ICRP published revised recommendations 1991
» Consultants, Senior experts meetings, ad hoc
working groups, technical committees 1991, 1992, 1993
» 6th draft circulated to all member states March 1994
» 7th Draft approved by IAEA Board of Governors Sept 1994
» Publication of Interim Version S.S.115I 1994
» Formal approval by co-sponsoring organizations 1994-1996
» Publication of S.S.115 1996
» Revised publication GSR Part 3 July 2014
IAEA Basic Safety Standards
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IAEA Basic Safety Standards
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IAEA Basic Safety Standards
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Sponsoring organisations
» THE EUROPEAN COMMISSION (EC)
» THE FOOD AND AGRICULTURE ORGANIZATION OF THE
» UNITED NATIONS (FAO)
» THE INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)
» THE INTERNATIONAL LABOUR ORGANIZATION (ILO)
» THE NUCLEAR ENERGY AGENCY OF THE OECD (NEA)
» THE PAN AMERICAN HEALTH ORGANIZATION (PAHO)
» THE UN ENVIRONMENT PROGRAMME (UNEP)
» THE WORLD HEALTH ORGANIZATION (WHO)
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Objectives
These Standards establish requirements for the protection of
people and the environment from harmful effects of ionizing
radiation and for the safety of radiation sources.
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Scope
» Radiological effects of ionizing radiation
» Applies to all controllable exposure situations
» Applies to occupational, public and medical exposure
The GSR
Part 3
applies to
Occupational
exposures
Medical
exposures
Existing
exposure
situations
Planned
exposure
situations
Emergency
exposure
situations
Public
exposures
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Requirements
» Parties with responsibilities for protection and safety shall
ensure that the principles of radiation protection are
applied for all exposure situations
» Responsibilities are defined for
– Government
– Regulatory body
– Persons and organisations responsible for facilities
and activities that give rise to radiation risks
– Management
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Regulatory body
» Assessment of notifications for permission to conduct
practices that entail or could entail exposure to radiation
» Authorization of relevant practices and the sources
associated with them, subject to specified conditions
» Periodic inspection for compliance with conditions
» Enforcement as necessary to ensure compliance with
regulations and standards
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Graded approach
The application of the requirements in planned exposure
situations shall be commensurate with the characteristics of the
practice or the source within a practice, and with the magnitude
and likelihood of the exposures.
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National regulations
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The European Union
» The EU is an economic and political partnership between 28 European
countries
» It was founded in 1958 to foster economic cooperation and to avoid conflicts
» Today it is an organisation with common policy in many areas
» The EU is based on the rule of law, founded on treaties
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The European Union
» The European Council sets the EU's overall political
direction – but has no powers to pass laws
– Current president Herman Van Rompuy
» There are 3 main institutions involved in EU legislation
– the European Parliament, which represents the EU’s
citizens and is directly elected by them
– the Council of the European Union, which represents
the governments of the individual member countries
– the European Commission, which represents the
interests of the Union as a whole
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EU agencies
» There are a number of specialised European Union
agencies which offer information or advice to the EU
institutions, the Member States and citizens. Each of
these agencies has a specific technical, scientific or
managerial task. EU agencies can be grouped into
several categories.
» Euratom agencies and bodies work within the framework
of the European Atomic Energy Community Treaty
(Euratom) to coordinate research in the EU countries on
the peaceful use of nuclear energy and to ensure that the
supply of atomic energy is both sufficient and secure.
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EU directives
» EU directives lay down certain end results that must be
achieved in every Member State
» Directives are used to bring different national laws into
line with each other, and are particularly common in
matters affecting the operation of the single market (e.g.
product safety standards)
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EU directives
» Directive 13/59/Euratom
– 5 December 2013
– Laying down basic safety standards for protection
against the dangers arising from exposure to ionising
radiation
» Repealing the previous
– Directive 96/29/Euratom – ionizing radiation, 1996
– Directive 97/43/Euratom – medical exposure, 1997
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Radiation protection in radiotherapy
» Occupational exposure
– Protection against occupational exposure
– Categorization of controlled and supervised areas
– Classification of workers
» Public exposure
– Restricted areas and shielding
» Medical exposure
– Justification and treatment optimisation
– Accident prevention
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Occupational and public exposure
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Occupational exposure
» Three fundamental possibilities to reduce exposure
– Exposure time
– Distance from source
– Shielding
» For occupancy in a given area shielding is the only option
» It is recommended to use designated areas
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Designated areas
» Controlled area
– “A defined area in which specific protection measures
and safety provisions are or could be required for
controlling exposures or preventing the spread of
contamination in normal working conditions, and
preventing or limiting the extent of potential
exposures.”
» Supervised area
– “A defined area not designated as a controlled area
but for which occupational exposure conditions are
kept under review, even though no specific protection
measures or safety provisions are not normally
needed.”
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Controlled area
» In radiotherapy, controlled areas include
– All treatment rooms
– Brachytherapy source preparation rooms
– Source storage areas
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Supervised area
» In radiotherapy, supervised areas include
– Operator consoles (shielded)
– Locations where calculated exposure rates through
barriers may result in doses of 1 mSv per year
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Requirements
» Restricted access
» Warning signs
» Staff monitoring
» Interlocks (where appropriate)
» Operating and emergency procedures
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Failing interlocks
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Classification of workers
» ICRP recommends the classification of areas of work
rather than the classification of workers
» For any worker who usually works in a controlled area, or
who occasionally works in a controlled area and may
receive a significant dose from occupational exposure,
individual monitoring shall be undertaken where
appropriate, adequate and feasible
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Classification of workers
» For any worker who regularly works in a supervised area
or who enters a controlled area only occasionally, the
occupational exposure shall be assessed on the basis of
the results of workplace monitoring or individual
monitoring, as appropriate
» In addition, additional controls have to be considered to
protect the embryo/fetus of pregnant workers
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Classification of workers
» According to the EU directive 13/59 a distinction is made
between two categories of exposed workers
– category A: those exposed workers who are liable to
receive an effective dose greater than 6 mSv per year
or an equivalent dose greater than 15 mSv per year
for the lens of the eye or greater than 150 mSv per
year for skin and extremities
– category B: those exposed workers who are not
classified as category A workers
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The design of radiotherapy installations
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Radiotherapy facility
» Different types of working areas
– Controlled areas
– Supervised areas
– Non-designated areas
» Clear separation
– Warning signs
– Interlock systems
– Patient observation and communication
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Careful planning
» The aim is to restrict dose to workers and the public to
acceptable levels
» Clarify clinical goals and future plans regarding treatment
types, equipment, estimated workload, etc.
» Conservative assumptions should be used
» Verification of the assumptions and design criteria
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Shielding requirements
» Depend on
– Type and placement of the treatment unit
– Direction of the primary beam
– Location of the operator
– Occupancy of neighboring areas
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Shielding requirements
» Shielding can be reduced by
– Placing treatment rooms underground
– Placing treatment rooms together
– Using large treatment rooms
» Issues
– Room entrance
– Ventilation
– Cable ducts
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Shielding materials
» Low-energy gamma and x-rays: Lead
» High-energy (>500 keV) gamma and x-rays: Concrete
» Electrons: Photon shielding is adequate
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Shielding calculations
» Primary radiation
» Scattered radiation
– Mainly from the irradiated patient
– May be difficult to calculate
» Leakage
– Escaping the through the collimators
– Depend on equiment design
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Primary and secondary barriers
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Brachytherapy
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Barrier thickness
» The thickness is calculated in terms of tenth-value layers
TVLnt
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Barrier thickness
» The thickness is calculated in terms of tenth-value layers
eTVLnTVLt )1(1
MV Material TVL1 (cm) TVLe (cm)
6 Concrete 37 33
Steel 10 10
Lead 5,7 5,7
10 Concrete 41 37
Steel 11 11
Lead 5,7 5,7
18 Concrete 45 43
Steel 11 11
Lead 5,7 5,7
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Attenuation factor
» The number of TVLs is calculated from the attenuation factor
where the attenuation factor is given by
)log(Bn
WUT
PdB
2
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Attenuation factor
» P is the design goal (Sv / week)
» d is the distance from the source (m)
» W is the workload (Gy / week)
» U is the use factor
» T is the occupancy factor
WUT
PdB
2
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Conservative assumptions
» The attenuation of beam through the patient is neglected
» The barrier thickness is calculated based on normal
incidence
» The leakage from the linac head is 0.1% (maximum
allowed by the IEC)
» High occupance factors are assumed for non-designated
areas
» The calculation point is assumed to be close to the barrier
(0.3 m)
» Extra margins for unknown situations
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Design goals
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Design goals
SWEDEN
0.1 mSv in one year
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New department in Lund
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New bunkers
Primary
beam
18 MV
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Example calculation – primary barrier
Point of
interest18 MV
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Example calculation – primary barrier
» The design goal: P=2 mSv / week
» Distance from source: d=6 m
» The workload: W=1200 Gy / week
» The use factor: U=0.25
» The occupancy factor: T=1/40
WUT
PdB
2
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Example calculation – primary barrier
» The design goal: P=2 mSv / week
» Distance from source: d=6 m
» The workload: W=1200 Gy / week
» The use factor: U=0.25
» The occupancy factor: T=1/40
62
106.9 WUT
PdB
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Example calculation – primary barrier
m 23.2
02.5)log(
106.9 62
TVLnt
Bn
WUT
PdB
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Example calculation – secondary barrier
Point of
interest
18 MV
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Example calculation – secondary barrier
» For leakage radiation
» The design goal: P=0.1 mSv / week
» Distance from source: d=6 m
» The workload: W=1200 Gy / week
» The occupancy factor: T=1
3
2
10
WT
PdB
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Example calculation – secondary barrier
» For leakage radiation
m 83.0
52.2)log(
100.310
3
3
2
TVLnt
Bn
WT
PdB
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Example calculation – secondary barrier
» For scattered radiation
» dsca is the distance from source to patient
» dsec is the distance from patient to point of interest
» a is the scatter fraction defined at dsca
» F is the field area at dsca
)400/(
2
sec
2
FWT
dPdB sca
a
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Example calculation – secondary barrier
» For scattered radiation
)400/(
2
sec
2
FWT
dPdB sca
a
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Example calculation – secondary barrier
42
sec
2
1023.1)400/(
FWT
dPdB sca
a
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Example calculation – secondary barrier
m 75.1
91.3)log(
1023.1)400/(
42
sec
2
TVLnt
Bn
FWT
dPdB sca
a
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Example calculation – secondary barrier
» The ”two-source” rule:
– If the thickness required to protect from leakage differs
from that required to protect from scatter by less than one
TVL, use the greater thickness and add one HVL of
shielding material for the energy of the leakage radiation
– If the two thicknesses for leakage and scatter protection
differ by more than one TVL use the greater thickness
» In our case the two calculations differ with more than one
TVL, so we use the greater one (t=1.75 m)
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Roof
» Even if there is no activity on the floor above the bunker,
adequate shielding in the ceiling is important
» Radiation scattered in the air above the facility (so called
skyshine) may otherwise make a significant contribution
to persons in neighboring areas (public)
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Maze
Point of
interest
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Transmitted primary radiation
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Patient scattered radiation
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Scattered leakage radiation
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Leakage transmission radiation
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Total dose at maze entrance
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Doors
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Neutrons
» At high energy linacs (> 10 MeV) neutron production must
be considered
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Neutrons
» Neutrons are high-LET particles
» Activated elements may contribute to the neutron dose
received by persons entering the treatment room
» However, most elements likely being activated have short
half-lives, and a waiting period of 1 min will reduce
activated radiation levels with one half
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Neutrons
» Concrete is a good neutron shield due to its water content
(4-5%)
» After moderation neutrons can be stopped by elements
with high thermal neutron capture cross section (boron)
» Heavy metals do not provide good shielding for neutrons,
but can be needed to attenuate capture gammas
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Contruction phase
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Radiation survey
» Verification that construction proceeds as planned and
approved
» There may be construction errors
» Final inspection and radiation survey
– Installation
– Preliminary survey
– Acceptance
– Full radiation survey
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Survey equipment
» A Geiger-Müller counter may be useful to find leakage
radiation
» Absolute measurements require ion chambers
» Above 10 MV, neutron survey should be performed
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Measurement points
» Primary and secondary barriers
» Maze entrance
» Junctions and ducts
» Scanning for defects
» Special procedure
» Outside the facility
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Measurements
» Use worst conditions
– Maximum field size
– Highest energy with highest penetration
– Lowest energy with most scatter
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Evaluating the efficacy of the shielding
» Based on measured dose rate
» Applying relevant values for
– Workload
– Use factor
– Occupancy factor
» Local rules may be needed
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Medical exposure
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Patients
» Patients are subject to medical exposure
» Dose limits do not apply
» Treatments should be
– Justified
– Optimised
» In radiotherapy, potentially lethal doses of radiation are
delivered to patients
– Risk of mistreatments or accidents
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Justification
» The seriousity of the primary disease
» The proability of cure
» The probability and seriousity of complications
» The patient’s decision
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