Radiation Risk Assessment
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Transcript of Radiation Risk Assessment
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Radiation Protection Course for Radiation Oncology Residents.
Radiation Risk Assessment
Mara Pinto Monedero
Medical Physicist
Kantonsspital Aarau (KSA)
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Contents
o Introductiono What is Risk Assessment?
o Hazards identificationo Interaction of ionizing radiation with tissues
o Ionizing Radiation Effects
o Dose-response relationo Linear Quadratic Model
o Linear Threshold Model
o Linear No Threshold Model
o Exposure assessmento Radiation exposure in medicine
o
Risk characterization
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
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Introduction
Risk analysis process
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Health risk assessment from the nuclear accidentafter the 2011 Great East Japan Earthquake andTsunami. WorldHealth Organozation(WHO).
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What is Risk Assessment?
Risk assessmentpredicts the likelihood of occurrence of adverseevents from a defined exposure based on scientific evidence.
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Hazard Identification
o Dose-Response relationship
o Exposure assessment
o
Risk characterization
Type and nature of adverse effects that radiation can cause.
Relationship between radiation exposure andadverse health effects that can cause.
Measure or estimate the intensity, frequency, andduration of human exposure to radiation.
Estimate qualitatively or quantitatively the risk of adversehealth effects under defined exposure conditions.
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Hazard Identification
Ionizing Radiation
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Electromagnetic radiation (UV, X-Rays, Gamma Rays)
Particulate radiation (atomic or subatomic particles)
Radiation with sufficient energy to cause ionization in the medium.
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Hazard Identification
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Sources Ionizing Radiation
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Hazard Identification
Sources Ionizing Radiation
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
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Hazard Identification
Sources Ionizing Radiation
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
1980 USA Population 2006 USA Population
Total Dose (mSv) 2.98 6.24
Natural 80.5% 49.7%
Medical 17.8% 48.1%
Others 1.5% 2.2%
Medical Exposures % of Total Exposures % Medical Exposures
CT Exams 24.0% 50.0%
Nuclear Medicine 12.8% 26.7%
Diagnostic X-Ray 4.8% 10.0%
Interventional Radiology 6.4% 13.3%
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Hazard Identification
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Sources Ionizing Radiation
https://www.naz.ch/en/aktuell/tagesmittelwerte.shtml
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Hazard Identification
Ionizing Radiation Effects
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Interactions with tissue
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Hazard Identification
Ionizing Radiation Effects
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Interactions with tissue
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Hazard Identification
Ionizing Radiation Effects
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Deterministic (Non-Stochastic) Effects
o Stochastic Effects
Somatic (Cancer).
Hereditary Defects.
Severity increases with dose.
Mechanism involves effects (often cell kill) on many cells.
No threshold.
Dose threshold.
Probability increases with dose but severity is independent of dose.
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Dose-Response Relationship
Dose
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o The amount of radiation deposited within the body.
o The amount of energy deposited per unit of mass (Unit: Gy)
o The biological response to an agent (radiation), i.e. a change
in structure, function, morbidity or mortality.
Response
Dose-Response Models
o A mathematical description of the relationship between
dose and response.
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Dose-Response Relationship
What is consideredlow/high dose?
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
The National Academy of Sciences in their
Biological Effects of Ionizing Radiation reports
(BEIR), as well as other scientificorganizations that study effects of radiation,
use a definition of low dose to be between
0.1-0.15 Sievert (Sv).
Doses above 1 Sv are considered high
doses.
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Dose-Response Relationship
What is the Evidence?
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Radiogenic cancer elevated risk is currently only
consistently able to be demonstrated in those groups of
study populations exposed to high-dose radiation (>1 Sv).
o Cancer and other health effects have not been observedconsistently at low doses (
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Dose-Response Relationship
What is the Evidence?
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Mayor epidemiologicalinvestigations that form thebasis of current cancer dose-response estimates inhuman populations areshown in the table.
o In this studies most individuals
received a large dose.
o Extrapolation (using models)
to low dose level.
Difficult to quantify risks from low
doses directly.
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Dose-Response Models
Low Dose Extrapolation
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Cell culture and animal studies
have provided information
demonstrating tumorigenesis
from high levels of radiation
exposure.
o At lower dose levels bothdeterministic and stochastic
effects are not observed or the
studies have not been
comprehensive enough.
Risk for cancer induction at low dosemust be extrapolated from the high
dose data
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Dose-Response Models
Linear Quadratic Model
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Assumes that the incidence ofinduced cancer at low doselevels increase linearlywithradiation dose up to a certain
level.
o At high dose levels, theincidence increases muchmore rapidly (quadraticrelationship)
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Dose-Response Models
Linear Threshold Model
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Assumes that damage is directlyproportional (linear)to the doseof radiation at all dose levels.
o
There is athresholdbelowwhich too few cells are affectedor cellular repair mechanismcompensate for any damagethat occurs.
o Threshold near 0.01-0.5 Sv
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Dose-Response Models
Linear No-Threshold Model (LNT)
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Assumes that damage is
directly proportional (linear)to
the dose of radiation at all
dose levels.o No Threshold.
This is the most conservative
approach for radiation protection and
this hypothesis is used by advisoryand regulatory agencies .
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Exposure Assessment
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in Radiology
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Exposure Assessment
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in Radiology
Ionizing Radiation Diagnotstic Procedures
Diagnostic
Procedure
Effective dose
(mSv)
Equivalence in
thorax X-Ray
Equivalence in natural
radiation background
(Madrid)
X-Ray Extremity < 0,01
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Exposure Assessment
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in Radiology
Ionizing Radiation Diagnotstic Procedures
Diagnostic ProcedureEffective dose
(mSv)
Equivalence in
thorax X-Ray
Equivalence in natural
radiation background (Madrid)
Lumbar Column (AP) 1,3 65 8 months
Intravenous Pyelogram
(IVP)2,5 125 15 months
X-Ray Upper GI tract 3 150 43 months
X-Ray Lower GI tract 7 350 3,5 years
Head CT 2,3 115 1 year
Thorax CT 8 400 4 years
Abdomen/Pelvis CT 10 500 5,1 years
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Risk characterisation
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in RadiologyProbability of mortal cancer induction in different diagnostic
procedures (per 1000000 exposures)
Procedure Cases
RX Abdomen AP 25
RX Lumbar Spine AP 36
RX Lateral Lumbar Spine 16
RX Mamography (one proyection) 5
RX Thorax PA 1
RX Thorax Lateral 2
RX Lower GI Tract 236
RX Coronary Angioplasty 1100
RX Ablation 850
RX Thorax-Abdomen-Pelvis CT 690
RX Abdomen CT 430
NM Bone Gammagraphy 300
NM Pulmonary Gammagraphy 330
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Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in RadiologyProbability of mortal cancer induction in different diagnostic
procedures (per 1000000 exposures)
The excess of risk is low, considering the natural risk of developing a cancer
(almost one case per four population)
The benefits of a diagnostic procedure always overcome the risk, if the
procedure isjustified.
The risks of NOT performing an exam include missing a diagnosis and/or
initiating treatment too late to improve the medical outcome.
The potential life reduction due to the disease of concern in conjunction
with the latency period for radiation induced cancer needs to be considered
relative to the normal life expectancy of the patient.
Risk characterisation
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Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in Radiology
Risk characterisation
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Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in RadiologyVirtual Colonoscopy
o Alternative colorectal cancer screening tool
o Concern about potential radiation risks
o Effective dose 8 mSv per screen
o Screening 50-80 every 5 years
8 to 28 radiation-related cancers per 10,000 screened
360 to 520 cancers prevented per 10,000 screened
Risk characterisation
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Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in RadiologyRisk comparison
Risk characterisation
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Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in RadiologyRisk comparison
Risk characterisation
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Exposure Assessment
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in Radiation Oncology
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Exposure Assessment
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in Radiation Oncology
o Simulation
Imaging radiation
o CT imaging, 4D-CT
o PET imaging, PET-CT imagingo
IGRT: kV- Imaging, Cone Beam-CT, MV Imaging.o Imaging during radiation therapy (gating, tracking)
Therapeutic radiation
o Radiation therapy
o Intensity Modulated Radiation Therapy (IMRT)
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Exposure Assessment
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in Radiation Oncology
Dose for 1 exposure
0.1-1 mSv
kV imaging MV imaging
Treatmentwith 30fractions and twosetup fields:
Dose for 1 exposure
0.5-5 mSv
Dose: 6-60 mSv
Treatmentwith 30fractions and two
setup fields:
Dose: 30-300 mSv
IGRT kV imaging vs MV imaging
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Exposure Assessment
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in Radiation Oncology
Dose for 1 CT:
10-20 mSv
kV Cone Beam CT MV Cone Beam CT
Treatmentwith 30
fractions and one CB-CT:
Dose for 1 CT:
20-50 mSv
Dose: 300-600 mSv
Treatmentwith 30
fractions and one CB-CT:
Dose: 600-1500 mSv
IGRT Cone Beam CT
Attention!: Local doses can be large!
Example: H&N irradiation 3-5 Gy extra parotid dose
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Exposure Assessment
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in Radiation OncologyImaging dose vs Therapeutic Dose
Hlgt RA.Assesment of Therapeutic, Scatter and Imaging Doses in radiation Oncoloy and Implications for
Cancer Risk. Dissertation ETH Zrich.
Scheme CBCT Portal MV Planar kV-kV Planar kV-MV
Scheme CBCT 26/23 8/0 0/0 0/0
Scheme kV-kV 0/0 8/0 26/23 0/0
Scheme kV-MV 0/0 8/0 0/0 26/23
Scheme MV 0/0 20/20 0/0 0/0
Fractionation
3D-CRT 26 x 2.0 Gy = 52Gy
IMRT,VMAT 23 x 2.2 Gy = 60.6 Gy
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Exposure Assessment
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Radiation exposure in Radiation OncologyImaging dose vs Therapeutic Dose
Hlgt RA.Assesment of Therapeutic, Scatter and Imaging Doses in radiation Oncology and Implications forCancer Risk. Dissertation ETH Zrich.Local relative increase of dose because of the applied
imaging scheme varies between below 0.5% and 30%.
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Risk characterization
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Second cancer: histologically distinct cancer that develops afterthe first cancer.
o Second cancer account for 6%-10% of all cancer diagnoses in USA
o With the new treatment modalities (IMRT, IMAT, proton and heavy
ion therapy), larger number of secondary cancers are expected.
Risk of secondary malignacies after radiotherapy
Increase in long term survivors who are at risk of developing second cancer.
Increase in beam-ON time (IMRT) to deliver the same target dose but
different dose distribution: Low dose to a large volume .
Secondary neutron dose in proton and heavy therapy and in photon therapy
E> 10 MV.
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Risk characterization
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Risk factors for second cancers
Age
o Increased susceptibility of tissue to mutagenic effect of therapy.
o Higher rate of cell proliferation during early stages of development.
o Longer period of follow up, which allows second cancer withtypically long latencies to emerge.
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Risk characterization
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Risk factors for second cancers
Age
Children are 2-3 times more sensitive to the
effects of radiation exposure as compared with a
middle age person, and 5-10 times more sensitive
compared to the elderly.
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Risk characterization
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Risk factors for second cancers
Gender
o Female sex is associated with increased risk of second primarycancers.
E.g: increased of secondary breast cancers, increased occurrence of
thyroid cancer in female survivors.
Others
o Certain chemoterapeutic agents.
o Familiar cancer syndromes.
o Gene-environment interactions.
o Lifestyle choices.
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Latent Period of Cancers
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Latent period: time interval between irradiation and occurrence of
malignancy.
The risk and the length of the latent
period depend on the persons age at
the time of exposure.
Risk characterization
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Epidemiology of Second Primary Cancers after Radiation Therapy
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Most radiation-associated cancers develop within or at the edge of
the radiation field.
Risk characterization
o
o
o sarcomas, lung-, bladder- and rectal cancer in patients receiving
RT for prostate cancer.
o
brain tumors or prophylaxis irradiation.
o sarcomas, skin-, breast- and thyroid cancer after pediatricprimary cancer.
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Observations with Hodgkin-patients
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Cumulative cancer risk for a patient irradiated at 30 years, at the
age of 60.
Risk characterization
Males: 18% (Comparison to general population: 7%)
Females: 27% (Comparison to general population: 9%)
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Uncertainties in Estimate ofCancer Risk
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o Extrapolation to low dose or low dose rate exposure.
o Population transfer models.
o Age at the time of exposure and projection to lifetime risk.
o Dosimetry uncertainties.
o Missclasification of cancer.
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Risk characterization
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o BEIR VII -Health Risks from Exposure to Low Levels of IonizingRadiation- US population (2006)
o UNSCEAR- Effects of Ionizing Radiation-multiple populations
(2008)
o
Health Protection Agency- Risk of Solid Cancers followingRadiation Exposure: Estimates for the UK Population -UK (20011)
Risk Assessment Reports
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Take Home Points
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
o LNT model accepted by advisory and regulatory agencies for
risk assessment in radiation protection.
o LNT might overestimated the incidence of induced cancer at
low doses.
o Evidence is:
o Radiation risk studies are affected by high uncertainties.
o Importance of justification and optimization.
D>1Sv, higher risk of developing radiogenic cancer.
D< 0.1Sv, developing of radiogenic cancer has not been consistently
demonstrated.
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Bibliography
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Health risk assessment from the nuclear accident after the 2011 Great East
Japan Earthquake and Tsunami, based on a preliminary dose estimation.
World Health Organization (2013).
Low-dose Extrapolation of Radiation-related Cancer Risk. International
Comission of Radiation Protection (ICRP) publication 99.
Effects of Ionizing Radiation. United Nations Scientific Committee on the
Effects of Atomic Radiation (UNSCEAR) Report to the General Assembly,
2006.
Risk of Solid Cancers following Radiation Exposure: Estimates for the UK
Population. Report of the independent Advisory Group on Ionising
Radiation. Health Protection Agency.
Schneider U. Modeling the Risk of Secondary Malignancies after
Radiotherapy. Genes 2011 (2) 1003:1049.
Hlgt RA.Assesment of Therapeutic, Scatter and Imaging Doses in radiation
Oncoloy and Implications for Cancer Risk. Dissertation ETH Zrich.
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Bibliography
Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
RSNA/AAPM Physics Modules: Estimating Cancer Risk from Imaging
Procedures. Hendde W, OConnor MK.
RSNA/AAPM Physics Modules: Radiaton Dose and Risk. Peck D, Applegate K,
Slovis T.
RSNA/AAPM Physics Modules: Radiaton Effects. Brown K, Parlade A, Dunne
A.
Nickoloff E et al. Radiation Dose Descriptors: BERT, COD, DAP, and other
Strange Creatures. Radiographics 2008 (28): 1439-1450.
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Radiation Risk Assessment. Radiation Protection Course for Radiation Oncology Residents.
Thank you for your attention