Health Physics: Chapter 3 Radiation Protection M.Mupparapu, DMD Professor Division of Oral and Maxillofacial Radiology Department of Diagnostic Sciences [email protected]

Brenner DJ, Hall EJ. Computed Tomography- An increasing source of radiation exposure. N Engl J Med2007; 357: 2277-84.

Radiation Sources • • •

Natural Artificial Other

Average annual exposure to U.S. population Total E = 3.6 mSv (.36 rem) (1 rem= 10 mSv)

Effective doses • • • •

REM

Calculate the equivalent organ dose(Ht) Ht = Absorbed dose X Quality factor Apply organ weighting factors(Wt) to dose Effective dose = sum of all organ doses x weighting factors E=Ht x Wt

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Natural background radiation • • • •

Radon (2mSv) Cosmic(0.27) Internal (0.39) Terrestrial(0.28)

55% 8% 11% 8%

Total from all natural sources

82%

Diagnostic dental radiation contributes to only about 1% of total dose from the healing arts( Aroua et al, 2002)

Radon (Rn) Periodic table

Radon •

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Radon, a decay product in the uranium series, is estimated to be responsible for approximately 56% of the radiation exposure of the U.S. population. It is the largest single contributor to natural radiation (2.0 mSv). The ubiquitous noble gas radon (radon-222) is transported in the water and air that enter our homes and buildings and by itself does little harm. Radon decays to form solid products that emit α-particles (218Po, 214Po, 214Pb, and 214Bi). These decay products become attached to dust particles that can be deposited in the respiratory tract, contributing an average annual equivalent dose to the bronchial epithelium in the U.S. population of 24 mSv. Exposure to this quantity of radiation may cause as many as 10,000 to 20,000 lung cancer deaths per year in the U.S., mostly in smokers.

Radiation detection

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Terrerestrial radiation •

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Cosmic radiation

It is estimated that the average terrestrial exposure rate is about 0.28 mSv per year, or approximately 8% of the average annual E to a person living in the U.S. This quantity of radiation exposure appears minimal compared with that received by individuals living in certain towns and villages of coastal Brazil and India, where the gamma radiation dose levels can be as high as 13 mSv per year. These unusually high terrestrial radiation levels are caused by a high content of Thorium-232 in the soil.

Risk Estimates E= 0.50mSv(500µSv)

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In the lower atmosphere the E from cosmic radiation is primarily a function of altitude, almost doubling with each 2000-meter increase in elevation, At sea level the exposure from cosmic radiation is about 0.24 mSv per year, whereas at an elevation of 1600 m (approximately 1 mile, or the elevation of Denver, CO), it is about 0.50 mSv per year; and at an elevation of 3200 m (approximately 2 miles, or the elevation of Leadville, CO), it is about 1.25 mSv per year. Considering the altitude and latitude distribution of the U.S. population and a 20% reduction in exposure because of structural shielding during time spent indoors, the average cosmic radiation E rate is about 0.26 mSv per year An airline flight of 5 hours in the middle latitudes at an altitude of 12 km may result in a dose equivalent of about 25 µSv.

Food and water ingestion • The second largest source (11%) of natural radiation results from the ingestion of food and water that contain radionuclides. The average annual E due to the presence of uranium and thorium and their decay products (primarily potassium-40, but also rubidium-87, carbon-14, tritium, and a dozen or more extraterrestrially produced radionuclides) is estimated at 0.4 mSv per year in the U.S. • An interesting source of internal exposure is the Brazil nut. This nut has relatively high concentrations of radioactive nuclides. A person consuming 100 g of Brazil nuts per week (not an unreasonable amount in Brazil) would receive an annual dose of 0.2 mSv.

E from FMS = 33 µSv E from Panoramic exposure = 26 µSv Total E = 59 µSv

Approx dose received from drinking water:

10-60 micro Sieverts Water quality consumer report Sent by the New Jersey American Water company Camden County, NJ

Alpha activity>15pci/L Treat Alpha activity 5-15 pci/L Test Aplha activity < 5 pci/L Do nothing

Water softening by: -Ion exchange system -Reverse osmosis

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What’s the risk from these alpha emitters? U.S.Environmental Protection Agency(EPA) has estimated that the additional lifetime risk associated with drinking water that contains the maximum contaminant level for gross alpha and radium 226+228 is about 1 in 10,000

Artificial sources • X-ray diagnosis (0.39) • Nuclear medicine (0.14) 4% • Consumer products (0.10) 3%

11%

Total from artificial sources 18% OTHER SOURCES: (less than 2%) Occupational (400)rare earth screen-film systems or digital imaging systems of equivalent or greater speed shall be used (NCRP, 2004) Panoramic x-ray machines shall be capable of operating at exposures appropriate for high-speed ( >400) rare-earth screen-film systems or digital image receptors of equivalent or greater speed(NCRP,2004) The above guidelines hold true to cephalometric radiography as well. Soft tissue filters shall be placed at the x-ray source rather than at the image receptor.

Image receptors of speeds slower than ANSI speed Group E films shall not be used for intraoral radiography. Faster receptors should be evaluated and adopted if found acceptable (NCRP, 2004)

• kV • mAs

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Processing the film Protection of personnel

Exposure reduction • •

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Exposure reduction • •

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Patient selection Choice of equipment – Image receptors – Film/Screen combinations – SSD – Collimation – Filtration – Lead aprons and thyroid collars Choice of technique – Operating the equipment

Source to image receptor distance for intraoral radiography shall not be less than 20 cm and should not be less than 40 cm(NCRP #145, 2004)

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Processing the film Protection of personnel

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Exposure reduction • •

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Patient selection Choice of equipment – Image receptors – Film/Screen combinations – SSD – Collimation – Filtration – Lead aprons and thyroid collars Choice of technique – Operating the equipment

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Collimator

Rectangular collimation of the xray beam, shall be routinely used for intraoral radiography

Film holding device

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Posterior Periapical and Bitewing

Processing the film Protection of personnel

Anterior Periapical and Vertical Bitewing

Position Indicating Device

Exposure reduction • •

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Patient selection Choice of equipment – Image receptors – Film/Screen combinations – SSD – Collimation – Filtration – Lead aprons and thyroid collars Choice of technique – Operating the equipment

The purpose of filtration is to remove the low-energy x-ray photons selectively from the x-ray beam. This results in decreased patient exposure with no loss of radiologic information Rare earth materials+ Al = good beam filtration , but dose by >50% = 70 kVp 70 -80 kVp 80-100 kVp

• kV • mAs

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Processing the film Protection of personnel

1.5 mm Al 2-2.3 mm Al 2.3-2.7 mm Al

Exposure reduction • •

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Patient selection Choice of equipment – Image receptors – Film/Screen combinations – SSD – Collimation – Filtration – Lead aprons and thyroid collars Choice of technique – Operating the equipment

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Current data show that the mean exposure at skin entrance for a single dental periapical film is 217 mR. If the gonad dose is equal to 1/10,000 of the total beam exposure, dose from one dental periapical film would be 0.02 mR. This is 50 times less than the negligible dose. ALARA >90% of scatter is absorbed by the aprons and shields

• kV • mAs

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Processing the film Protection of personnel

Thyroid shielding should be provided for all when it does not interfere with the examination

Exposure reduction • •

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Patient selection Choice of equipment – Image receptors – Film/Screen combinations – SSD – Collimation – Filtration – Lead aprons and thyroid collars Choice of technique – Operating the equipment

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The operating potential of dental xray machines should be >60kVp and no practical usage if > 80kVp. kVc machines should be in the operating range of 60-80

Exposure reduction • •

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• kV • mAs

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Processing the film Protection of personnel

Patient selection Choice of equipment – Image receptors – Film/Screen combinations – SSD – Collimation – Filtration – Lead aprons and thyroid collars Choice of technique – Operating the equipment

• For machines operating at 70 kVp, the mAs range for E speed films is about 3.6-4.2

• kV • mAs

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Processing the film Protection of personnel

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Exposure reduction • •

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Patient selection Choice of equipment – Image receptors – Film/Screen combinations – SSD – Collimation – Filtration – Lead aprons and thyroid collars Choice of technique – Operating the equipment • kV • mAs

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Processing the film Protection of personnel

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Film processing should be performed under the manufacturer-recommended conditions with proper processing equipment and a darkroom with safelights. Alternatively, an automatic processor with an appropriate safelight hood may be used

Exposure reduction • •

• Dark room QC – Sensitometry & Dosimetry – Step wedge – Reference film

• Chemistry • Maintenance of day light processors

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Patient selection Choice of equipment – Image receptors – Film/Screen combinations – SSD – Collimation – Filtration – Lead aprons and thyroid collars Choice of technique – Operating the equipment • kV • mAs

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• Protection of the operator – – – – –

• Protection of the public – Total E < 1mSv per year

Processing the film Protection of personnel

Exposure reduction

Exposure reduction • •

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Patient selection Choice of equipment – Image receptors – Film/Screen combinations – SSD – Collimation – Filtration – Lead aprons and thyroid collars Choice of technique – Operating the equipment

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• kV • mAs

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Exposure reduction • •

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Patient selection Choice of equipment – Image receptors – Film/Screen combinations – SSD – Collimation – Filtration – Lead aprons and thyroid collars Choice of technique – Operating the equipment • kV • mAs

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Processing the film Protection of personnel Digital Image Postprocessing

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Radiographic technique for digital imaging shall be adjusted for the minimum patient dose required to produce an appropriate signal-noise ratio to provide the best image quality Underexposure results in decreased signal-noise ratio with loss of diagnostic information as the image becomes grainy

Shielding design Barriers Distance Position Personal Dosimeters

Processing the film Protection of personnel

Shielding by increasing the thickness of the building materials by adding lead, gypsum, drywall, concrete, steel etc. Operator should stand atleast 2 m from the tubehead during exposure Barriers should be designed to provide visual contact and communication with patient during the procedure. Safe area: Scatter radiation will be at minimum 45°from the primary beam as it exits from patient. Scatter is at maximum 90-180° as it enters the patient.

Recent Advances: Laser lights renders radioactive waste safe Central Laser Facility Rutherford Appleton Laboratory Chilton, Didcot, Oxfordshire, OX11 0QX

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New research at the University of Strathclyde, England

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Using a laser, Professor Ken Ledingham has successfully transformed one of the deadliest products of nuclear fission into inert matter in minutes.

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The Vulcan laser, housed at the Rutherford Appleton Laboratory near Oxford has enabled Prof Ledingham and his team to use nothing more than the focused energy contained in light to excite the nucleus of the iodine 129 isotope, with a radioactive half life of 15.7 million years.

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When hit with laser light the isotope becomes totally inert and safe to handle in less than an hour.

Wed 6 Aug 2003

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