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Introduction

• is indispensable in modern medicine • The radiographic examination is one of the principal diagnostic method used in all fields of medical services Overview of Radiation • The risk associated with low-level diagnostic exposures could be low, but greater than zero Protection • For this reason it is required to measure the dose in the diagnostic radiology

Principles of radiation protection, dose limits

Bálint Vecsei dr.

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The aim of radiation protection in dentistry is to obtain the Introduction desired clinical information with minimum radiation exposure to patients, dental personnel, and the public.

• Radiographic examinations play an essential part of dental practice.

• The use of X-rays is an integral part of clinical dentistry • On the majority of patients some form of radiographic examination is necessary • „The clinician's main diagnostic aid.”

• The range of knowledge of dental radiography can be divided conveniently into four main sections: – Basic physics and equipment – Radiation protection – Radiography – Radiology

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• Every day all over the world people are exposed to ionising radiation, almost all from natural sources in the environment or for medical reasons. • A (abbreviated BED) is an informal expression of • Ionising radiation has enough energy to cause damage cells which can increase the risk ionising radiation exposure, intended as a general educational example to of cancer later in life. indicate the potential dose due to naturally occurring radioactive • In general the health effects of ionising radiation are dependent on the received dose. by eating one average sized banana. However, in practice this dose is not • Several different terms and units have been used in dosimetry over the years. cumulative as the principal radioactive component is excreted to maintain metabolic equilibrium. The BED is only an indicative concept meant to show the existence of very low levels of natural radioactivity within a natural food, and is not a formally adopted dose quantity.quantity.

The concept probably originated on the RadSafe nuclear safety mailing list in 1995,[original research?] where a value of 9.82×10−8 or about 0.1 μSv was suggested for a 150 gram banana.

Natural sources account most of the radiation we all receive each year

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Units of radiation and radioactivity

In order to quantify how much radiation we are exposed to in our daily lives and assess potential health impacts as a result, it is necessary to establish a unit of measurement.

• The basic unit of radiation dose absorbed in tissue is the gray (Gy), where one gray represents the deposition of one joule of energy per kilogram of tissue.

• However, since neutrons and alpha particles cause more damage per gray than gamma or beta radiation, another unit, the (Sv) is used in setting radiological protection standards. This unit of measurement takes into account biological effects of different types of radiation. • One gray of beta or gamma radiation has one sievert of biological effect, one gray of alpha particles has 20 Sv effect and one gray of neutrons is equivalent to around 10 Sv (depending on their energy). • Since the sievert is a relatively large value, dose to humans is normally measured in millisieverts (mSv), one thousandth of a sievert.

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Everyone is exposed to some form of Estimated annual from the environment in which we live. doses from various sources of radiation: 2,4-3,4 mSv/year Natural background radiation • Cosmic radiation from the earth's atmosphere • Diagnostic radiology represents the largest source of artificial • Gamma radiation from the rocks and soil in the earth's crust radiation which is comparable to natural background exposure • Radiation from ingested radioisotopes, e.g. 40K, in certain foods • Recently, patient exposure to medical and dental X-ray • Radon and its decay products, 222Rn is a gaseous decay product of that is examination has grown rapidly present naturally in granite. As a gas, radon diffuses readily from rocks through soil and can be trapped in poorly ventilated houses and then breathed into the lungs

Artificial background radiation • Fallout from nuclear explosions • discharged from nuclear establishments • Medical and dental diagnostic radiation • Radiation from occupational exposure.

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Recently, patient exposure to medical and dental X-ray examination has grown rapidly!

Radiologic and Nuclear Medicine Studies in the United States and Worldwide: Frequency, Radiation Dose, and Comparison with Other Radiation Sources—1950–2007

Global annual per-capita effective radiation dose from various sources for (a) 1980 –1984 (11) and (b) 1997–2007 (15). Bkd background.

U.S. annual per-capita effective radiation dose from various sources for (a) 1980 and (b) 2006 by using UNSCEAR value of 2.4 mSv for natural background (Bkd) (for a, NCRP 1987 estimated value, 3.0 mSv; for b, NCRP 2009 estimated value, 3.1 mSv).

Radiology: Volume 253: Number 2—November 2009 ▪ radiology.rsna.org 11 12

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Annual dose of natural background radiation in Cosmic radiation dose ratio at different heights different countries

International air travel (8000m) 3,7 µSv/hour Supersonic aircraft (15000m) 13 µSv/hour

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Exposure to certain flight routes • (Based on measurements by different airlines) The risk associated with diagnostic exposures greater than zero • For this reason it is prerequisite to measure the dose to the patients in the diagnostic radiology precisely. Route Total effective dose (μSv) • The radiation dose to the Zágráb - Ontarió 35,1 New York - Florida 18,9 patients should be as low as Buenos Aires - Újzéland 57,2 Amsterdam - Tokió 55,6 reasonably achievable, a Amsterdam - Milánó 4,8 principle known as ALARA Helsinki - New York 34,8 Koppenhága - Bangkok 23,0 (International Commission on Koppenhága - Stockholm 2,2 Brüsszel - Johannesburg 28,4 Radiological Protection) Brüsszel - Tokió 83,0 Frankfurt - Brakheim 13,5 • The number of diagnostic Frankfurt - New York 30,3 Frankfurt - Chicago 40,4 examinations should also be Budapest - New York 62,9 X 15 = 0,9435 mSv taken into consideration because Budapest - Beijing 56,4 Budapest - Bangkok 37,9 the risk is directly proportional to the frequency of X-ray exposure.

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Effects of radiation are grouped into two categories • Dental radiographic examinations are one of the most • Deterministic- frequently performed radiological studies. – effects are based on cell killing and are characterized by a • The effective dose delivered to patients per radiograph is low threshold dose. Below the threshold dose there is no but the collective dose is significant because of the large clinical effect. With exposures above the threshold dose number of radiographs made. the severity of the injury increases with dose. • Stochastic- – effects, including cancer and heritable effects are based on damage to DNA. There is no-threshold or ‘‘safe’’ dose.

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Three types of exposure

Persons are medically exposed as part of their • Medical Exposure diagnostic or treatment (principally the exposure of persons as part of their According to ICRP and BSS, two basic principles of diagnostic or treatment) radiation protection are to be complied with: • Occupational Exposure justification and optimization (exposure incurred at work, and practically as a result of Dose limits are not applicable, but a guidance is work) given on dose levels (Administrative limit!) • Public Exposure (including all other exposures) Investigation of exposures is strongly recommended

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Framework of radiological protection Three levels of justification for medical exposure • General level: • Justification – No practice should be adopted unless its – The use of radiation in medicine is accepted as doing more introduction produces a positive net benefit. good than harm

• Optimization • Generic level: – All exposures should be kept as low as – reasonably achievable, economic and social Specific procedure with a specific objective (eg. chest factors being taken into account. radiographs for patients showing relevant symptoms)

• The use of doses limits • Third level: – The exposure of individuals should not – The application of the procedure to an individual patient exceed the limits recommended for the appropriate circumstances.

Dose constraints and guidance (or reference) levels ARE RECOMMENDED

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Justification for an individual patient Generic justification (third level) • It is a matter for national professional bodies, • To check that the required information is not yet sometimes in conjunction with national regulatory available authorities • The exposures to staff (occupational) and to • Once the procedure is generically justified, no members of the public should be taken into account additional justification is needed for simple • The possibility of accidental or unintended exposures diagnostic investigations (potential exposure) should also be considered • The decisions should be reviewed from time to time • For complex procedures (such as CT, IR, etc) an as new information becomes available individual justification should be taken into account by medical practitioner (radiologist, referral doctor..)

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Benifit and risk The optimization of protection

 Optimization is usually applied at two levels: – The design and construction of equipment and installations – Day to day radiological practice (procedures)

 Reducing the patient dose may reduce the quantity as well as the quality of the information provided by the examination or may Benifit Risk require important extra resources

 The optimization means that doses should be “as low as reasonably achievable, economic and social factors being taken into account” compatible with achieving the required objective

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Overview of dose quantities Estimated lifetime risk as a function of age

Radiation Physical Chemical Bio-chemical Biological effect effect effect effect

Absorbed dosis

Equivalent dose RISK Effective dose

• Reflects the combined detriment from stochastic effects due to the equivalent doses in all the organs and tissues of the body • The combination of probability and severity of harm is called “detriment”.

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Changes in Dose Limits (ICRP)

Radiation mSv 500

400 We live with Can kill 2-5 mSv 4000 mSv 300

200

Where to stop, where is the safe point? 100 What are the effects of radiation? 0 1931 1947 1977 1990 Year

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Dose constraints for medical exposure Dose constraints

• For medical exposure dose constraints should • for medical research purposes only be used in optimizing the protection of • for individuals helping in care, support or persons exposed for medical research comfort of patients, and visitors purposes, or of persons, other than workers, – 5 mSv during the period of the examination or who assist in the care, support or comfort of treatment exposed patients. – 1 mSv for children visiting

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PUBLIC - Optimization under Occupational dose limits Constraints • DOSE LIMITS • 20 mSv/year effective dose • effective dose of 1 mSv in a year • in special circumstances, effective dose of 5 • BUT does not allowed over 50 mSv in any mSv in a single year, provided that the average year! over five consecutive years in less than 1mSv per year • equivalent dose to lens of the eye 15 mSv in a Whole body!? year • equivalent dose to skin of 50 mSv in a year.

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Dose Limits (ICRP 60) Dose Limits (ICRP 60)

Occupational Public Students, trainee (16-18 years) Effective dose 20 mSv/yr averaged * 1 mSv in a yr Effective dose 6 mSv/yr over 5 yrs. Annual equivalent Annual equivalent dose to dose to ► Lens of eye 15 mSv ► Lens of eye 20 mSv 15 mSv ► Skin 150 mSv ► Skin 500 mSv 50 mSv ► Hands & Feet 150 mSv ► Hands & Feet 500 mSv

N.B.: M.P.D. 1931 = 500 mSv, 1947=150 mSv, 1977=50 mSv & N.B.: M.P.D. 1931 = 500 mSv, 1947=150 mSv, 1977=50 mSv & in 1990=20 mSv in 1990=20 mSv Public dose limits are more strict, because young, old and pregnant peoples are involved!

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Personal Dosimetry Comparison of doses from sources of exposure Source of Exposure Dose Dental X-ray 0.005 mSv 135g bag of Brazil nuts 0.005 mSv Personal dosimetry provides the means to Chest X-ray 0.02 mSv Transatlantic flight 0.07 mSv measure and record radiation doses received by Nuclear power station worker average annual occupational exposure 0.18 mSv individual workers. UK annual average radon dose 1.3 mSv CT scan of the head 1.4 mSv Personal dosemeters should be worn by UK average annual radiation dose 2.7 mSv USA average annual radiation dose 6.2 mSv operators who take more than 100 intra-oral CT scan of the chest 6.6 mSv films or 50 panoramic films per week. Average annual radon dose to people in Cornwall 7.8 mSv

Whole body CT scan 10 mSv In practice, the majority of dentists and support Annual exposure limit for nuclear industry employees 20 mSv staff do not need to wear dosemeters although Level at which changes in blood cells can be readily observed 100 mSv many do so as a reassurance measure. Acute radiation effects including nausea and a reduction in white blood cell count 1000 mSv

Dose of radiation which would kill about half of those receiving it in a month 5000 mSv

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Qualitative risk levels • Negligible risk: less than 2 days of natural background exposure • Minimal risk: more than 2 days and up to 1 month of natural background exposure • Very low risk: more than 1 month and up to 8 months of natural background exposure • Low risk: more than 8 months and up to 6 years of natural background exposure • Moderate risk: more than 6 years of natural background exposure

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Thank you for your attention!

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