An optimized imaging protocol for orofacial cleft patients

Abstract The objective was to present an optimized imaging protocol for orofacial cleft (OFC) patients, which might be used as an international recommendation for OFC care programs. The present radiological protocol has been structured by the OFC team of the University Hospitals Leuven based on a combined approach of clinical experience and scientific evidence. The development was based on careful monitoring of the existing needs for radiological diagnosis by the involved disciplines. Needs were revised by expert consensus and radiological optimization. Effective doses were converted to panoramic equivalents (professional conversion) and background radiation (patient conversion). At the age of 6, a panoramic radiograph is taken for the evaluation of dental anomalies. For the preoperative planning of secondary alveolar bone, grafting a low‐resolution cone beam computer tomography (CBCT) of a limited field of the maxilla is taken at the age of 7 to 9. At the age of 10, 15, and 20, a low‐resolution CBCT of both jaws with the smallest possible field is taken serving as conventional, presurgical, and end of treatment records, respectively. Two‐dimensional images are reconstructed out of 3D ones. There are currently no international guidelines concerning the imaging protocol for OFC patients. It is clear that a multidisciplinary approach plays a key role in radiation hygiene. In this article, we presented an optimized imaging protocol for OFC patients based on European guidelines to accomplish the concepts of justification and optimization, which might be used as an international recommendation for OFC care programs.

One important aspect in the OFC care program is diagnostic imaging. Given the multidisciplinary setting, different radiological projections may be required for diagnostic, presurgical, and postoperative assessment by different specialties throughout the lifespan of an OFC patient. The latter may lead to cumulative radiation throughout childhood and adolescence that means an increased radiation risk Pauwels et al., 2014a).
Because of this, OFC protocols should strive for optimized imaging during the various treatment phases up until adulthood.
Surprisingly, there are no international guidelines in literature concerning such longitudinal imaging protocol for OFC patients.
The aim of this article is to present an optimized imaging protocol for OFC patients, which might be used as an international recommendation for OFC care programs. Subobjectives include justification of the required imaging steps and optimization of the related radiation doses versus required image quality at various time points throughout the entire treatment of the OFC patient.

| MATERIALS AND METHODS
The present imaging protocol has been structured by the OFC team of the University Hospitals Leuven, based on a combined approach of clinical experience and scientific evidence.
According to the European guidelines for OFC patients (Shaw, Semb, Nelson, Brattstrom, & Molsted, 2001), clinical records (radiographs, study casts, intraoral, and extraoral photographs) should be taken for treatment planning, monitoring, and evaluation. Records are collected at the age of 6 (start of treatment), 10 (conventional treatment planning), 15 (presurgical records), and 20 (end of the craniofacial growth). The development of this standardized imaging protocol was based on careful monitoring of the existing needs for radiological diagnosis by the different specialists involved in the team.
Needs were revised by expert consensus and radiological optimization.
A first action (expert consensus) consisted of moving the necessary time points indicated by the different specialties, up until a level where these would better overlap. The second action (radiological optimization) aimed to optimize the imaging characteristics and the radiological protocol adapted to the diagnostic needs for each specific time point. This optimization included resolution (high resolution = HR or low resolution = LR), nature of the image (two-dimensional = 2D or three-dimensional = 3D), and anatomical field of view (FOV). After critical appraisal, the timing and settings of the needed radiographs were carefully adjusted to accomplish the concepts of optimization and justification.
Instead of emphasizing the absolute value of the effective dose ranges, we converted them to panoramic equivalents for professionals and background radiation for patients (Oenning et al., 2017). For this conversion, we used 10 μSv for one panoramic radiograph and 5,1 mSv background radiation per year (Bornstein, Scarfe, Vaughn, & Jacobs, 2014).

| RESULTS
Optimization included a reduction in the number of images, selection of low-dose imaging techniques, and limiting the required FOV as much as possible. Table 1 provides a summary of the present optimized imaging protocol for OFC patients. Table 2 represents the effective dose ranges of the discussed imaging steps converted to panoramic equivalents and background radiation.
Generally, before the age of 6, treatment of OFC patients consists of clinical interventions that do not require any radiological projections.
At the age of 6, a panoramic radiograph is taken to evaluate dental anomalies such as impaction, missing or supernumerary teeth, caries, and the position of the maxillary lateral incisor. The planning of secondary alveolar bone grafting (SABG) depends on the position of the maxillary lateral incisor. If it is located in the premaxilla, the bone graft is performed in function of the root formation of the maxillary canine. If the maxillary lateral incisor tends to erupt in the lateral segment, an early SABG is planned. In case of more complex pathologies and syndromes involving craniofacial structures (e.g., hemifacial microsomia, Pierre Robin sequence, craniosynostosis, and early childhood caries), a panoramic or 3D radiograph is taken at an earlier age (Anderson, Yong, Surman, Rajion, & Ranjitkar, 2014).
At 7 to 9 years old, SABG needs to be performed to restore the alveolar defect, permitting canine eruption through the bone graft.
This is ideally planned when the root of the unerupted canine is a half to two-thirds developed (Oh, Park, Choi, Kwon, & Koh, 2015).
For preoperative planning of SABG, a low-resolution CBCT of the maxilla is taken (Figure 1). The limited FOV (generally 8 × 5 cm 2 ) minimizes radiation exposure to radiosensitive structures such as the eye lens and the thyroid gland. Three-dimensional evaluation of the alveolar cleft enables insight in size, shape, and volume of the cleft and its relationship with anatomical structures, thereby increasing the procedure's predictability (Choi et al., 2012). It has been shown that low-dose protocols are sufficient to achieve these goals (Oenning et al., 2017). both jaws with the same settings as described above is taken. Also, a panoramic radiograph and lateral cephalogram are reconstructed out of this 3D image. The extent of the skeletal discrepancy will be decisive for the maxillofacial surgeon and orthodontist to decide upon the need for orthognathic surgery. In case of normal craniofacial growth, orthodontic treatment is the final treatment stage, and these will serve as final records. In case there is skeletal class III due to maxillary growth restriction, orthognathic surgery is indicated once maxillofacial growth has been completed. Residual craniofacial growth is estimated on the reconstructed lateral

| Justification
Traditionally, 2D radiographs have been used for diagnostic purposes in OFC teams. Since the introduction of 3D imaging in dentistry, CBCT scans started to gain popularity especially in the field of maxillofacial surgery since the reliance on 2D radiographs is acknowledged to be problematic in presurgical planning and postoperative assessment of alveolar clefts, bone bridges, and cleft-adjacent teeth as a consequence of trying to derive complex 3D structures from a 2D image.
The information derived from 3D images is advantageous over the conventional approach by excluding many factors affecting image quality and reliability, such as enlargement, distortion, structural overlap, and positioning problems. Literature is unanimous that 3D imaging improves diagnosis, treatment planning, and treatment outcomes in OFC patients. Vital diagnostic information such as amount and quality of available bone, complex tooth eruption scheme, or position of impacted teeth cannot be accurately assessed on 2D images (Choi et al., 2012;European Commission, 2012;Jacobs, 2011). Therefore, a higher accuracy of the records can be achieved leading to a higher predictability of interventions by several disciplines.
In the Eurocleft project as well as the Americleft project, recommendations regarding imaging were found to be missing or out of date. We believe that these outdated documents should be updated, and that the present imaging protocol could serve as a guideline.
One could think that 3D imaging implies increased cumulative radiation dose compared with several 2D images. Following the As Low As Reasonably Achievable (ALARA) principle, cumulative radiation dose should be limited through the years, especially in pediatric patients being more sensitive to radiation Oenning et al., 2017). Complying with this principle for the multidisciplinary treatment approach of OFC patients was the main goal of the present protocol.
Evidence-based CBCT guidelines for dental and maxillofacial radiology published by the European Commission (SedentexCT) were consulted during the development of this imaging protocol (European Commission, 2012). Although this is a comprehensive document, the guidelines for OFC patients are scarce. Therefore, we implemented the general concepts by applying them on this specific population.
According to those guidelines, the use of CBCT is justified for OFC patients as the effective dose is reduced up to 12.

| Optimization
Several image optimization measures were implemented to ensure adequate image quality at the lowest achievable dose (Pauwels, 2015).
First, the overall amount of exposures in the lifespan of an OFC patient was reduced. We restructured the former policy of excessive uncoordinated exposures (both 2D and 3D) by different disciplines leading to high cumulative doses . A massive cumulative dose reduction was obtained by attuning all disciplines with a request for imaging to each other. One carefully selected CBCT image is able to yield all requested information for several disciplines, Finally, motion artifacts are a recurrent issue as they can negatively influence image quality. An ongoing prospective study in our institution showed that these artifacts are commonly seen in OFC patients, directly related to age and psychological maturity. The older the patients were, the less frequent motion artifacts occurred.
Syndromes including mental retardation may also need to be considered when deciding upon a certain radiological projection. Although the scanning device can be adapted to immobilize the patient by providing a stable chair, handgrips, a bite block, a chin, and headrest, the role of the operator should not be underestimated. The operator should have experience with pediatric patients to be able to comfort them during positioning and exposure. In case the FOV should contain the maxilla only, a bite block can be used to improve patient's stability.
Bite blocks are not allowed during a CBCT scan of both jaws as disclusion disturbs the reliability of cephalometric measurements. In case there is evidence of motion during scout viewing, it may be better to postpone the radiograph to a later date.
Although an imaging protocol based on chronological ages serves as a backbone, we must keep in mind that every patient should be considered individually. Several factors such as dental age, maturity, cleft type and severity, and other pathologies influence the extent of the treatment strategy as well as the timing and type of radiographs.
Also, we realize that an imaging protocol is center-specific since it depends on the clinical protocol used.
A panoramic radiograph can sometimes be delayed in function of dental maturity. In case of an early SABG, the CBCT for preoperative SABG planning is made earlier. Therefore, standard deviations on the average chronological ages do exist.
The involvement of the alveolar ridge is an important determinant in the imaging protocol. In patients with unilateral cleft lip and palate, bilateral cleft lip and palate, and cleft lip and alveolus, the present imaging protocol is followed. In patients with cleft lip (CL) and cleft palate (CP), conventional 2D radiographs are usually sufficient because bone grafting and orthognathic surgery are indicated less frequently.

| CONCLUSIONS
There are currently no international guidelines concerning the imaging protocol for OFC patients. It is clear that a multidisciplinary approach plays a key role in radiation hygiene. In this article, we presented an optimized imaging protocol for OFC patients based on European guidelines to accomplish the concepts of justification and optimization, which might be used as an international recommendation for OFC care programs.