Deterministic effects are of no concern in diagnostic dental radiation however, stochastic (or probabilistic) effects are of concern. The relative risks for these effects are calculated from epidemiological data in cohorts such as the Life Span Study or survivors of atomic bombings and data on radiation-induced cancers from medically exposed populations (International Commission on Radiological Protection, 2007; United Nations Scientific Committee on the Effects of Atomic Radiation, 2017).
The paediatric population is more susceptible to the risks of ionising radiation for several reasons such as a higher mitotic activity and longer life-expectancy (in comparison to adults). Also, children have smaller sized heads which places their thyroid and brain closer to the dental area being imaged during conventional dental radiography. There are several dental radiography techniques for paediatric patients encompassing planar and cross-sectional imaging.
The aim of this systematic review was to evaluate the effectiveness of all radioprotective measures in underage patients who undergo a dental radiographic diagnostic examination. The authors undertook this study to aid the European Academy of Paediatric Dentistry (EAPD) in the renewal of radioprotective guidelines for dental radiology in children.
This review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement. Searches for existing guidelines on radiation protection in paediatric dentistry were conducted in SIGN, AHRQ, NICE, Australian Clinical Practice Guidelines, AAPD, EAPD< IAD-MFR, AAOMR, BSDMFR, imagegently, MEDLINE (PubMed), EMBASE, Web of Science, SciELO, Scopus and LILACS. Systematic reviews, meta-analyses, randomised controlled trials or cluster trials, cohort studies, cross-sectional studies, case-control studies and comparative in-vitro research were also considered. Dental radiography techniques included were; bitewings, peri-apicals, occlusal, panoramic and cephalometric radiographs and cone beam computed tomography (CBCT). Radioprotective measures such as thyroid shielding, lead apron, collimation, lead glasses device settings and film type were of interest. Risk of Bias was assessed using Methodological Index for Non-randomised Studies (MINORS) and study quality reported using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. If studies were homogenous in terms of design and comparator, a meta-analysis was conducted using a random-effects model.
- 18 studies were included, 15 underwent qualitative synthesis and regression analysis performed on 3 studies.
- The risk of bias assessment demonstrated a varied range from 9-15 / 20 points. The quality of methodology was high and well reported in only seven studies, all others had insufficient methodological quality. 15 of 18 studies were in-vitro.
- Intraoral radiography:
- 3 in-vitro studies reported a reduction of the effective dose with rectangular collimation (compared to circular collimation).
- 1 study reported lower effective doses when thyroid shielding was used for a full mouth intra-oral series.
- One study reported lower effective doses when digital film was used compared to F-speed film.
- Panoramic radiography:
- There were differences in effective dose between different units.
- The use of a paediatric setting on the Orthopos unit reduced the maximum effective dose by 45.5% and in the PM 20002 CC, the reduction was 17%. The eye dose was reduced by changing from the adult to the paediatric setting by 60-90% using Orthopos however there was no change using the PM 2002 CC. The absorbed doses to the dental arches with both systems reduced using the paediatric setting. Doses to the thyroid gland using the Orthopos paediatric setting reduced the neck level by more than 50% on average and by as high as 80% just below the mandible. The PM 2002 CC paediatric program resulted in no appreciable change however when the tube voltage/current was changed from 64/5 to 60/4 kVcp/mA, there was a 10-30% reduction.
- The measured effective dose was 32% lower when a short collimation/paediatric setting was used (7.7µSv) compared to a long collimation/adult setting (11.4 µSv).
- The automatic exposure control (AEC) protocol resulted in an effective dose that was 10.5% higher than doses for short collimation/paediatric setting and 25% lower than doses for long collimation/adult setting.
- Cephalometric radiography:
- Mean significant differences in organ dose were significantly lowered for eye lenses, thyroid, submandibular and parotid glands.
- Skull radiography:
- The implementation of PA over AP projects provided a reduction of mean effective dose by 7.1-11.8% (depending on patient age).
- For AP, PA and lateral skull radiography, the excess lifetime cancer mortality risk was calculated to be (1.4–2.0) × 10−6, (1.3–1.8) × 10−6 and (1.2–1.6) × 10−6, respectively, depending upon the age of the child.
- Oblique lateral radiography:
- A focus to skin distance of 40cm showed a significant dose reduction compared to a focus to skin distance of 24cm.
- Reduction of the exposure time from 20ms to 16ms and finally 14ms also gave a significant reduction in the effective dose.
- Reduction of the horizontal angulations from 180° over 170°, 160°, 150°, 140°, 130°, 120° and finally 110° had a significant impact on effective radiation dose.
- Cone-beam computed tomography:
- The use of lead glasses reduced the absorbed dose by 67% for non-collimated scans and 39% for collimated scans. Thyroid shields showed a reduction in absorbed dose with the 0.125 mmPb (GrayShield™)-Barium sulphate equivalent shield showing significantly lower thyroid absorbed doses compared to other shields.
- The effective dose increases with the FOV dimension and was attributed to significantly higher doses for the brain, thyroid gland and red bone marrow.
- As studies used indirect measurements and outcomes, the quality of evidence was regarded as very low.
- Regression analyses was performed on three studies and the overall model suggested the effective dose explained 91.1% of the variance of the radiation dose depending on the FOV, mAs and kVp. Within this model, the effect of intensity and scan time was significant, increasing the effective dose linearly by 1.63 µSv per unit mAs. An exposure change from small FOV not containing the mandible to a small FOV containing the mandible increased the effective dose significantly.
The authors concluded: –
…The following radioprotective measures can reduce the exposure dose:For lateral cephalometry: collimation, filtration, the fastest receptor type and circumstantial thyroid shielding.
For oblique lateral radiographs: the shortest exposure time, a smaller horizontal angulation, a longer focus to skin distance.
For intraoral radiography: rectangular collimation, the fastest image receptor speed and thyroid shielding when the thyroid gland is in line of or very close to the primary beam.
For panoramic radiographs: collimation, the fastest receptor type and the use of automatic exposure control (AEC) or manual adjustment of intensity.
For cone-beam computed tomography: collimation, the largest voxels size in relation to the treatment need, change in image settings such as ultra-low dose settings, shorter exposure time, a lower amount of projections, lower beam intensity, reduction of the potential, use of a thyroid shield except in two situations and the use of AEC.
All of the changes in exposure parameters should be performed while maintaining a sufficient therapeutic value on an individual and indication-based level….
This is a substantial systematic review which evaluates the effectiveness of radioprotective measures in child patients undergoing dental radiodiagnostic examinations. Whilst the quality of evidence was commented by the authors as being low, they also acknowledged that high quality studies (e.g. randomised control trials) would be unethical and not feasible to perform. Dental professionals should aim to reduce the radiation dose, especially in paediatric patients and this review evaluates the radioprotective measures, which can be implemented based on the current available evidence.
Van Acker, J. W. G., Pauwels, N. S., Cauwels, R. G. E. C. & Rajasekharan, S. (2020) Outcomes of different radioprotective precautions in children undergoing dental radiography: a systematic review. European Archives of Paediatric Dentistry.
International Commission on Radiological Protection. (2007) The 2007 Recommendations of the International Commission on Radiological Protection. ICRP publication 103. Annals of the ICRP, 37(2-4), 1-332.
United Nations Scientific Committee on the Effects of Atomic Radiation. (2017) SOURCES, EFFECTS AND RISKS OF IONIZING RADIATION UNSCEAR 2017 Report [Online]. United Nations. Available: https://www.unscear.org/docs/publications/2017/UNSCEAR_2017_Report.pdf [Accessed 28 July 2020].