Estimation of paediatric organ and effective doses from dental cone beam CT using anthropomorphic phantoms

Objectives

Cone beam CT (CBCT) is an emerging X-ray technology applied in dentomaxillofacial imaging. Previous published studies have estimated the effective dose and radiation risks using adult anthropomorphic phantoms for a wide range of CBCT units and imaging protocols.

Methods

Measurements were made five dental CBCT units for a range of imaging protocols, using 10-year-old and adolescent phantoms and thermoluminescent dosimeters. The purpose of the study was to estimate paediatric organ and effective doses from dental CBCT.

Results

The average effective doses to the 10-year-old and adolescent phantoms were 116 μSv and 79 μSv, respectively, which are similar to adult doses. The salivary glands received the highest organ dose and there was a fourfold increase in the thyroid dose of the 10-year-old relative to that of the adolescent because of its smaller size. The remainder tissues and salivary and thyroid glands contributed most significantly to the effective dose for a 10-year-old, whereas for an adolescent the remainder tissues and the salivary glands contributed the most significantly. It was found that the percentage attributable lifetime mortality risks were 0.002% and 0.001% for a 10-year-old and an adolescent patient, respectively, which are considerably higher than the risk to an adult having received the same doses.

Conclusion

It is therefore imperative that dental CBCT examinations on children should be fully justified over conventional X-ray imaging and that dose optimisation by field of view collimation is particularly important in young children.Cone beam CT (CBCT) is an advancement of CT technology that has found wide application in dentomaxillofacial imaging. The ability of the CBCT systems to produce three-dimensional high-resolution images with diagnostic reliability has resulted in a significant increase in CBCT examinations in areas such as orthodontics, endodontics, periodontics, implantology, restorative dentistry, and dental and maxillofacial surgery [1-12]. However, CBCT imaging is associated with a higher radiation dose to the patient than panoramic and intra-oral imaging but a lower patient dose than conventional single and multislice CT [13-16]. Although radiation dose from CBCT is low relative to conventional CT, the radiation risk to the patient should be assessed and quantified. The radiation risk can be estimated by calculating the effective dose, which is a radiation quantity proposed by the International Commission on Radiological Protection (ICRP) [17].Several studies have estimated the effective dose for a range of CBCT units and imaging protocols [13-16,18-24]. The organ doses were measured with anthropomorphic phantoms and thermoluminescent dosimeters (TLDs). The ICRP 103 [25] tissue weighting factors were applied to organ doses to account for the tissue radiosensitivity. The ICRP 60 [17] and the revised ICRP 103 [25] tissue weighting factors have been used for studies before and after 2006, respectively. For the head and neck region, the ICRP 103 [25] factors include the salivary glands, oral mucosa and lymph nodes as radiosensitive organs that were not included in ICRP 60 [17]. In addition, the weighting factor of the remainder tissues was increased from 0.05 to 0.12. The published effective doses range from a few tens to several hundreds of microsieverts depending on the CBCT unit, the field of view and the position of the radiation field with respect to the radiosensitive organs.To the best knowledge of the authors, all the published studies on dental CBCT dosimetry have focused on effective doses to adult patients for a range of CBCT units and imaging protocols but none has estimated the organ and effective doses to paediatric patients. Children are more sensitive to radiation than adults because the number of dividing cells promoting DNA mutagenesis is higher and they have more time to express any radiation-induced effects, such as cancer. There is an order of magnitude increase in cancer risk between children and adults, and there is also a significant difference between boys and girls, with the latter being more radiosensitive [26,27]. Furthermore, a substantial proportion of dental X-ray procedures are performed in the paediatric group, notably in relation to orthodontics.The aim of this study was to measure paediatric organ doses and, hence, derive effective doses using two anthropomorphic phantoms and TLDs for a range of CBCT units and for standard imaging protocols.