Radiation Biology and Minimizing Risk · Sources of Radiation Exposure Natural Sources = 2.40 μSv...

Radiation Biology and Minimizing Risk

Radiosensitivity at the Cellular Level

There is a direct relationship between radiosensitivity and:

Cells with a high mitotic rate

Cells that undergo many future mitoses

Cells that are primitive and mulitpotential


Short term effect: Cell death

Long term effect: Fibrosis of vessel walls This leads to fibro-atrophy of tissue, loss of

function and decreased resistance to infections and trauma. (Very important in Radiotherapy)

Radiosensitivity at the Cellular Level


Understanding Risks Associated with X Radiation

Damage to cellular DNA is the primary cause of radiation induced cell death, carcinogenesis and heritable mutations

Radiosensitivity varies with cell type

Highly sensitive cells: have a high mitotic rate undergo many future mitoses are primitive/multipotential

Effects can be classified as deterministic or STOCHASTIC

Adapted from White SC and Pharoah MJ. Oral Radiology. 6th Ed. 2009. Mosby Elsevier.

High

Lymph Tissue

Bone Marrow

Mucosa

Intestine

Testes

Medium

Growing Bone and

Cartilage

Salivary Glands

Fine Vasculature

Lung/Kidney/Liver

Low

Optic Lens

Muscle


Cell and Organ Effects – Terminology

Somatic Effect:

Changes in cells and organs of patients



Deterministic Effect:

A somatic effect where the probability of the change and the severity of the change is related to radiation dose

Examples: erythema, mucositis, fibrosis



Stochastic Effect:

A somatic effect where the probability of effect is related to dose but the severity of the change is unrelated to dose

All or none effect

Examples: cancer, heritable effect


Deterministic Effect Stochastic Effect

Cause Cell DeathDNA Damage (sublethal)

Example Mucositis Cancer

Severity Dose RelatedNot Dose Related(All-or-None)

Threshold Dose Yes No*

Probability of Effect100% if above threshold

Dose Related Dose Probability


* One x-ray photon could lead to mutation leading to cancer


Dental Risk Implication

The primary concern is radiation induces cancer

Risk estimates are made from extrapolations from high dose, full body radiation disasters (Hiroshima, Nuclear Industry Accidents)

It is unknown if these extrapolations are accurate or appropriate



Nonetheless, since we are not certain there are no deleterious effects we must act responsibly and limit all exposures to only those required to assist in diagnosis and treatment. This is the ALARA Principle (As Low As Reasonably Achievable).


Detriment per Sievert Per 100

Cancer 5.5

Heritable Effect 0.2

Total 5.7

Age Group (Years) Multiplication Factor

< 10 3

10-20 2

20-30 1.5

30-50 0.5

50-80 0.2

80+ Negligible Risk


The Importance of Age


Tables from: Radiation Protection: Cone Beam CT for Dental and Maxillofacial Radiology. SEDENTEXCT Project. 2011.

Radiation Detriment:The total harm that would eventually be experienced by an exposed group and its descendants as a result of the group’s exposure to radiation from a source.

Important Dose Measurements

Absorbed Dose:

The amount of energy absorbed/kilogram

Measured in Gray (Gy)

Equivalent Dose:

Provides a method to compare different types of radiation.

For x-rays: Absorbed Dose = Dose Equivalent

Measured in Sieverts.


Important Dose Measurements

Effective Dose:

Effective dose measures the equivalent whole-body dose.

It allows risk comparisons from one region of the body to another.

Employs a tissue weighting factor

Weighting factors updated 2007

Measured in Sieverts.


Sources of Radiation Exposure

Natural Sources = 2.40 μSv

Medical Sources = 2.50 μSv

Dental Sources = <0.01 μSv

Dental x-ray examinations account for less than 1% of the average annual exposures from man-made sources.


Sources of Radiation Type Source Dose (Sv)

NaturalTerrestrial 2.40

Cosmic 0.40

Man-Made

Medical X-ray 2.00

Nuclear Medicine 0.50

Dental 0.01

Other 0.11

Man-made

Natural

Medical X-ray

Nuclear Medicine

Dental

Other

Cosmic

Terrestrial

Medical X-ray

Nuclear Medicine

Dental

Other



Risks Associated with Dental Radiographic Examinations

Examination Manufacturer Model Format SvProbability of x in a Million Fatal Cancers

Bitewing (4 Film) Planmeca Intra PSP/F Speed/Rectangular 5.0 0.3

Full Mouth Series (18 Film) Planmeca Intra PSP/F Speed/Rectangular 34.9 2

Full Mouth Series (18 Film) Planmeca Intra PSP/F Speed/Round 170.7 9

Full Mouth Series, (18 film) Planmeca Intra D Speed/Round 388.0 21

Panoramic Planmeca Promax CCD 24.3 1.3

Panoramic Sirona Orthophos XG CCD 14.2 0.8

Lateral CephalometricVarian

MedicalInterray PSP 5.6 0.3

PSP=Photostimulable Phosphor Plate; Rectangular/Round=Collimation; CCD=Charge-Coupled DeviceAdapted from Ludlow JB, Davies-Ludlow LE, White SC. Patient Risk Related to Common Dental Radiographic Examinations: The impact of 2007 International Commission on Radiological Protection Recommendations Regarding Dose Calculation. J Am Dent Assoc 2008;139:1237-1243.


Risks Associated with CBCT Examinations Large Field of View (> 15 cm)

Machine SvProbability

of x/1MFatal Cancer

i-CAT NG1 74.0 4

CBMercuRay1 569.0-1073.0

31-59

Kodak5 93.0-260.0

RANGE1,5 30.0-1073.0

Medium Field of View (>8 cm < 15 cm)


of x/1MFatal Cancer

Galileos1 70.0-128.0

4-7

i-CAT NG1 87.0 5

CBMercuRay1 407.0-510.5

31

Kodak5 76.0-166.0

RANGE1,2,4,5 48.0-510.5

Small Field of View ( 8 cm)

Machine SvProbability of

x/1M Fatal Cancer

Orthophos XG 3D 64 4

i-CAT Classic2,3 34.0-148.5

Promax 3D1,7 30.0-674.0

27-36

PreXion 3D1 189.0-388.0

10-21

RANGE1,2,3,6,7 30.0-674.0

1. Ludlow JB, Ivanovic M. Comparative dosimetry of dental CBCT devices and 64-slice CT for oral and maxillofacial radiology. Oral Surg, Oral Med, Oral Pathol, Oral Radiol, Endod. 2008;106:106-114.

2. Roberts JA, Drage NA, Davies J, Thomas DW. Effective dose from cone beam CT examinations in dentistry. Br J Radiol.2009;82:35-40.3. Loubele M, Bogaerts R, Van Dijck E, Pauwels, et al. Comparison between effective dose of CBCT and MSCT scanners for

dentomaxillofacial applications. Eur J Radiol. 2009;71:461-468.4. Ludlow JB. A manufacturer’s role in reducing the dose of cone beam compupted tomography examinations: effect of beam filtration.

Dentomaxillofacial Radiol. 2011;40:115-122.5. Okano T, Harata Y, Sugihara Y, Sakaino R, et al. Absorbed and effective doses from cone beam volumetric imaging for implant

planning. Dentomaxillofacial Radiol. 2009;38:79-85.6. Suomalainen A, Kiljunen T, Kaser Y, Peltola J, Kortesniemi M. Dosimetry and image quality of four dental cone beam computed

tomography scanners compared with multislice computed tomography scanners. Dentomaxillofacial Radiol. 2009;38:367-378.7. Qu XM, Li G, Ludlow JB, Zhang ZY, Ma XC. Effective dose of Promax 3D cone-beam computerized tomography scanner with different

dental protocols. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2010;110:770-776.

Multi-slice CT (MSCT)


of x/1MFatal Cancer

Somaton1 534.0-860.0

29-47

Range3 474.0-1110.0


Putting Risks in Perspective


ExposureRisk of Death

per Million

Hospital Stay after an accident 230

Choking 13

Boat Accident 4.6

Cancer from FMS (PSP/F/Round) 9

Reducing Patient Exposure

1. Selective Radiology

– Individualized prescriptions based on history, signs and symptoms and previous radiographs.



2. Lead Aprons and Thyroid Shields



3. CBCT Protocol– Use the smallest field-of-view available to answer the

clinical question

– Adjust the mAS and kVp for the clinical question and size of patient

– Do not use the same technique for all patients



4. Interpretation


The central consideration before exposing a patient to an x-ray examination is:

Benefit versus Risk

DiagnosisTreatmentResolution

Radiation DoseCostTime

More Tests


The central consideration after determining that an x-ray examination is required is:

A.L. A. R. A.As Low As Reasonably Achievable

Choosing the best study to answer the clinical question(s) with the smallest radiation dose

Best Most ComplexBest Most Expensive


Minimizing the Risks Associated with X-rays

“There is little evidence to support radiographic exposure of

all dentulous areas of the oral cavity in search of occult

pathoses in the asymptomatic patient.”American Dental Association Council on Scientific Affairs. The use of dental radiographs - Update and recommendations.

JADA.2006;137:1304-1312.

“Where there is no justification for a test, it should not be done.”Picard EI. Legal liability of doctors and hospitals in Canada. 2nd Ed. Carswell, Toronto. 1984;p.210.



“In prescribing radiographs, the practitioner must make a

judgment that is influenced by a balance between keeping the

number of exposures to a minimum while obtaining an

adequate number of radiographs for a complete diagnosis.

This means that the number, type and frequency should be

based individually for each patient’s clinical signs, symptoms

and past dental history. Radiographs should never be taken

solely for administrative purposes.”Royal College of Dental Surgeons. Guidelines - Dental Record Keeping. May 2008.



Individualized prescription is the rule

Radiographic caries screening is the exception


Choosing the appropriate radiographic examination requires

that the dentist consider the patient history, the clinical

findings, and planned treatment.

It also requires that the dentist have a fundamental

knowledge of dental, oral and systemic diseases and the

knowledge and ability to chose and expose only those

radiographs or series of radiographs that have a

likelihood to affect diagnosis and/or treatment.


Radiation Protection:

Cone Beam CT for Dental and Maxillofacial Radiology

Evidence Based Guidelines

SEDENTEXCT Project, 2011

SEDENTEXCT Project Members:

Included medical physicists, dentists, dental radiologists, experts in guideline

development, and industry representatives

51 Project members from the United Kingdom, Greece, Romania, Belgium,

Sweden and Lithuania


Radiation Protection: Cone Beam CT for Dental and Maxillofacial Radiology



1++High quality meta-analyses/systematic reviews of randomized controlled trials (RCT) or RCTs with very low risk of bias

1+ Well conducted meta-analyses/systematic review of RCTs, or RCTs with moderate risk of bias

1- Meta-analyses/systematic reviews of RCTs, or RCTs with high risk of bias

2++High quality systematic reviews of case-control or cohort studies; High quality non-randomized trials, case-control or cohort studies with a very low risk of confounding, bias, or chance and high probability that the relationship is causal

2+Well conducted, non-randomized trials, case-control or cohort studies with a moderate risk of confounding, bias, or chance and a moderate probability that the relationship is causal

2-Non-randomized trials, case-control or cohort studies with a moderate risk of confounding, bias or chance and a moderate probability that the relationship is causal.

3 Case series, surveys

4 Expert Opinion

Study Grading System – Adapted from Scottish Intercollegiate Guidelines Network


Radiation Protection: Cone Beam CT for Dental and Maxillofacial Radiology



A At least one meta-analysis, systematic review, or RCT rated as 1++, and directly applicable to the target population; or a systematic review of RCTs or a body of evidence consisting principally of studies rated as 1+ , directly applicable to the target population, and demonstrating overall consistency of results.

B A body of evidence including studies rated as 2++, directly applicable to the target population, and demonstrating overall consistency of results; or extrapolated evidence from studies rated as 1++ or 1+.

C A body of evidence including studies rated as 2+, directly applicable to the target population and demonstrating overall consistency of results; or extrapolated evidence from studies rated as 2++.

D Evidence level 3 or 4; or extrapolated evidence from studies rated as 2+.

GP Good Practice. (Based on clinical expertise of the guideline group and consensus stake holders)

Guideline Grading System – Adapted from Scottish Intercollegiate Guidelines Network


Examination Primary CBCT

SecondaryCBCT

Caries - -

Perio - +/-

Periapical - +/-

Endodontics - +/-

Dental Trauma - +/-

Orthodontics - -

Impaction - +/-

Exodontia - +/-

Implant +/- +/-

Bone Pathology - +/-

TMJ +/- +/-

Cleft Palate +/- +/-

Orthognathic Surgery +/- +/-

SEDENTEXCT 2011 Guidelines


Radiation Biology and Minimizing Risk · Sources of Radiation Exposure Natural Sources = 2.40 μSv...

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