www.fdiworlddental.org

www.fdiworlddental.org

Radiation Protection in Dental Radiology Training material developed by the International Atomic Energy Agency in collaboration with: World Health Organization, FDI World Dental Federation, International Association of DentoMaxillofacial Radiology, International Organization for Medical Physics, and Image Gently Alliance Protection of Workers and Public in Dental Radiology L12 IAEA International Atomic Energy Agency Educational Objectives Understands the scatter distribution for different radiographic modalities Identify the safest position of the operator and public relative to the patient and x-ray tube Understand the need for adequate distance and shielding, and be able to apply these principles in clinical practice

IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 2 Overview Protection from what? Dose limits / dose constraints Dose from scatter in dental radiography Principles of Protection Distance Time Shielding IAEA Radiation Protection in Dental Radiology

L12 Protection of Workers and Public in Dental Radiology 3 Overview Protection from what? Dose limits / dose constraints Dose from scatter in dental radiography Principles of Protection Distance Time Shielding IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 4

Protection from what? Protection from (decreasing order of importance): Scattered (S) radiation (source = patient) Primary (P) radiation (the X ray beam) Usually fully captured by image receptor Intra-oral radiography: slight discrepancy between beam size and detector size Leakage (L) radiation (from X ray tube) P S L X IAEA

Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 5 Overview Protection from what? Dose limits / dose constraints Dose from scatter in dental radiography Principles of Protection Distance Time Shielding IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology

6 Dose limits for workers and public One of the three principles of radiation protection: dose limitation International Basic Safety Standards, Requirement 12 (adopted): The government or the regulatory body shall establish dose limits for occupational exposure and public exposure, and registrants and licensees shall apply these limits. Dose limits established (& periodically revised) by ICRP (and subsequently incorporated into BSS and local legislation) See next slide IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology

7 Dose limits for workers and public Dose limits for occupational and public exposure, according to the current ICRP recommendations and International Basic Safety Standards (2014) Type of limit Annual effective dose Occupational 20 mSv 2,3 Public 1 mSv4 Annual equivalent dose to: Eye lens

20 mSv2 15 mSv Skin1 500 mSv 50 mSv Hands and feet 500 mSv - Averaged over 1 cm2, regardless of the area exposed. 2 Averaged over 5 consecutive years (100 mSv in 5 years), with no single year exceeding 50 mSv.

3 Additional restrictions apply for pregnant women. 4 Similar to the occupational dose, a higher annual dose could be allowed in a single year in special circumstances, providing that the average over 5 years does not exceed 1 mSv/year. 1 IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 8 Personnel monitoring The need for dose monitoring of workers handling dental X-ray equipment depends on: Local legislation Type and workload of equipment

Pregnancy of workers Different types of badges for monitoring available (film, TLD, OSL, MOSFET, ) Monitoring should be performed by a certified personnel dosimetry lab Corrective actions should be performed if any personnel dose approaches dose limits IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 9 Dose limits for workers and public Apart from dose limits, dose constraints can be applied Set separately for each radiation source Apply to occupational and public exposure Not dose limits but investigation levels:

exceeding a dose constraint does not represent non-compliance with regulatory requirements, but it could result in follow-up actions. IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 10 Overview Protection from what? Dose limits / dose constraints Dose from scatter in dental radiography Principles of Protection Distance Time

Shielding IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 11 Dose from scatter in dental radiography Intraoral radiography Office of Radiation Safety, Ministry of Health, New Zealand: 0.08-0.5 Gy at 1 m from patient (see figure on slide 21) Scatter for intra-oral radiography strongly depends on location (see further) IAEA

Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 12 Dose from scatter in dental radiography Intraoral radiography Portable intra-oral machines: local absorbed dose per exposure for operator 0.04-0.6 Gy (Danforth et al. 2009, Hermsen et al. 2008, McGiff et al. 2012, Pittayapat et al. 2010). Use of backscatter shield can reduce local doses 8-fold (McGiff et al. 2012) IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology

13 Dose from scatter in dental radiography Panoramic radiography Gijbels et al. (2005): 0.04-0.53 Gy at 1m CBCT SEDENTEXCT (2010): maximum scatter at 1m: 4.1-46.8 Gy (median for 10 CBCT models: 6.8 Gy), average scatter 2-8.1 Gy at 1m IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 14

Overview Protection from what? Dose limits / dose constraints Dose from scatter in dental radiography Principles of Protection Distance Time Shielding IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 15 Protection of Workers and Public Basic protection principles: Increase distance to radiation source Apply shielding (room & personal)

Limit the time spent in the vicinity of a radiation source IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 16 Principles of Protection Distance Inverse square law: beam intensity (I) reduces with the square of the distance (D) to the source Source I D

IAEA I/4 I/9 3*D 2*D Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 17 Principles of Protection Distance Intraoral, panoramic, cephalometric radiography: Distance >1.5 m annual dose to worker

<1 mSv (EC RP 136, 2004) >2 m distance from the patient often recommended If shielding is used: distance can be shorter CBCT: scattered radiation much higher; IAEA be installed in a protected enclosure must Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 18 Principles of Protection Apart from distance, location also matters! Scatter not homogenously distributed Diagnostic X-ray energy: tendency of scattering towards the forward (toward image receptor) direction

But: scatter is absorbed by patient as well! DISTRIBUTION OF X-RAY SCATTER (60 keV) TOWARDS IMAGE 0 RECEPTOR IAEA 90 PATIENT 270 Radiation Protection in Dental Radiology Relative amount of Compton scatter at each

angle) 180 TOWARD X RAY TUBE R. Pauwels L12 Protection of Workers and Public in Dental Radiology 19 Principles of Protection Scatter doses at 1 m (in Sv) for an intra-oral exposure made at 60 kV, 0.7 s, 200 mm focusto-skin distance Highest dose (due to backscatter) Lowest dose:

most of forward scatter is absorbed by patient IAEA Reproduced with permission by the Office Of Radiation Safety. Ministry of Health, New Zealand Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 20 Principles of Protection Dose rate (Sv/h) at 2 m from the patient (average from 3 intra-oral units) Highest dose in front of

patient (note: dose opposite to tube not measured) 373 344 366 X ray tube 62 144 212 102

IAEA Radiation Protection in Dental Radiology Lowest dose: directly behind X ray tube or behind patient Based on data from Tabakov et al. (2000) L12 Protection of Workers and Public in Dental Radiology 21 Principles of Protection For intra-oral exposures (general) Distance and shielding: more important than positioning

Avoid area opposite to X ray tube (high amount of scatter + possible primary radiation Avoid area behind X ray tube (tube itself provides shielding from backscatter, but surrounding area is prone to high amounts of scatter) When picking a location, keep as much patient tissue between yourself and the source of the scatter (i.e. the exposed region in the patient) At right angle to tube Patient acts as shielding IAEA 22 Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology Principles of Protection For intra-oral exposures (specific) Tube at side of patient: stand behind patient IAEA

Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 23 Principles of Protection For intra-oral exposures (specific) Tube diagonally toward patient: stand behind patient (90-135 to X ray beam) IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 24

Principles of Protection For intra-oral exposures (specific) Tube in front of patient: stand at either side of patient (90 or 270 to X ray beam) IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 25 Principles of Protection Panoramic radiography: little effect of position (Gijbels et al. 2005; anterior dose not measured) CBCT: depends on geometric factors (SEDENTEXCT, 2010) Sitting/standing devices: scatter distribution +/homogeneous for 360 rotations, lowest at tube

side for 180 rotations 180 360 rotation rotatio (X ray tube n at back of patient) IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 26 Principles of Protection CBCT: depends on geometric factors (SEDENTEXCT, 2010) Supine devices: lowest scatter in the

direction along the patients axis IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 27 Principles of Protection CBCT Absorption of scatter by the machine housing and patient can affect scatter distribution Scatter should be measured case-by-case; use of room shielding should always be preferred over picking the location with lowest scatter for CBCT equipment! IAEA

Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 28 Principles of Protection Variable patient (ergo: X-ray beam) orientation & machine housing in CBCT Sitting Standing Supine R. Pauwels IAEA Radiation Protection in Dental Radiology

L12 Protection of Workers and Public in Dental Radiology 29 Principles of Protection Shielding Room shielding & personal shielding Also protects: Patients (when not examined) Visitors, public Nearby people (e.g. office next to dentist) Material & thickness of shielding determines fraction of blocked radiation Should be tailored to national requirements, expert advise is required (see IAEA BSS) IAEA Radiation Protection in Dental Radiology

L12 Protection of Workers and Public in Dental Radiology 30 Principles of Protection Shielding materials Ok to use concrete or other conventional building materials (lead added in walls when needed; leaded glass can be used in windows) IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 31 Principles of Protection Shielding materials

Mobile or non-mobile shielding screens Courtesy of RAY-BAR IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 32 Principles of Protection Personal shielding Lead aprons 0.25-0.5 mmPb Subject to wear (cracks) Check for cracks using 2D radiograph of the apron Thyroid shields

Leaded glasses/gloves/caps Not used in a dental environment Image receptor should not be held by worker IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 33 Principles of Protection Time Cfr. Patient dose: dose ~ exposure time Exposure time should be adapted to patient (ALARA principle), not to the worker! But: time of worker in surrounding to radiation source can be limited e.g. rotation

schedule IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 34 Room Design Special room design considerations for CBCT equipment Design (i.e. shielding) of room depends on: X-ray equipment kV, mAs, ; workload; direction(s) of beam Organization of room Location of operator, location of public (e.g. surrounding rooms)

Amount of scattered radiation needs to be measured or estimated to determine shielding requirements IAEA Case-by-case basis, by qualified expert Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 35 Room Design Locations to measure scatter (marked as X) Example of dental CBCT room Corridor Waiting room CBCT

Treatment room Operator position Adjacent space (e.g. office, living area) IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 36 Room Design Shielding in CBCT (EC RP 172, 2012) IAEA Radiation Protection in Dental Radiology

L12 Protection of Workers and Public in Dental Radiology 37 References Danforth RA et al. (2009) Operator exposure to scatter radiation from a portable hand-held dental radiation emitting device (Aribex NOMAD) while making 915 intraoral dental radiographs. J Forensic Sci. 54:415-21. EC, European Commission (1999) European guidance on diagnostic reference levels (DRLs) for medical exposures. Radiation Protection 109. European Commission, Luxembourg. [https://ec.europa.eu/energy/sites/ener/files/documents/109_en.pdf] EC, European Commission (2004) European guidelines on radiation protection in dental radiology - The safe use of radiographs in dental practice, radiation protection publication 136 European Commission, Luxembourg. [https://ec.europa.eu/energy/sites/ener/files/documents/136.pdf] ICRP, International Commission on Radiological Protection (2007) The 2007 Recommendations of the International Commission on Radiological Protection. ICRP publication 103. Ann ICRP 37:1-332

ICRP, International Commission on Radiological Protection (2012) ICRP statement on tissue reactions and early and late effects of radiation in normal tissues and organs - threshold doses for tissue reactions in a radiation protection context. ICRP publication 118. Ann ICRP 41:1-322 IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 38 References Gijbels F et al. (2005) Dosimetry of digital panoramic imaging. Part II: Occupational exposure. Dentomaxillofac Radiol. 34:150-3. Hermsen KP et al. (2008) Radiation safety for the NOMAD portable X-ray system in a temporary morgue setting. J Forensic Sci. 53:917-21. McGiff TJ et al. (2012) Maintaining radiation exposures as low as reasonably achievable (ALARA) for dental personnel operating portable hand-held x-ray equipment. Health Phys. 103:S179-85. Pittayapat P et al. (2010) Image quality assessment and medical physics

evaluation of different portable dental X-ray units. Forensic Sci Int. 201:1127. SEDENTEXCT. Deliberable D2.2 - Completion of scatter dose measurements around CBCTs and recommendations for protective measures and positioning of CBCT units in dental offices. [http://www.sedentexct.eu/system/files/SEDENTEXCT %20D2.2%20v1%20FINAL_0.pdf] Tabakov et al. (2000) Instantaneous dose rate of scatter radiation in dental radiography. Phys Med16:27-30 IAEA Radiation Protection in Dental Radiology L12 Protection of Workers and Public in Dental Radiology 39

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