Dosimetry analysis of panoramic‐imaging devices in different‐sized phantoms R AD I A T I ON MEA S U R EM EN T S Dosimetry analysis of panoramic imaging devices in different sized phantoms Muizz A Wahi[.]
Received: November 2016 | Revised: 17 January 2017 | Accepted: 19 January 2017 DOI: 10.1002/acm2.12059 RADIATION MEASUREMENTS Dosimetry analysis of panoramic-imaging devices in differentsized phantoms Muizz A Wahid | Ella Choi | David S MacDonald | Nancy L Ford Oral Biological and Medical Sciences, The University of British Columbia, Vancouver, BC, Canada Author to whom correspondence should be addressed Nancy L Ford E-mail: nlford@dentistry.ubc.ca; Telephone: (604)822-6641 Abstract The aim of this study is to measure the radiographic dose in adult, adolescent, and child head-sized PMMA phantoms for three panoramic-imaging devices: the panoramic mode on two CBCT machines (Carestream 9300 and i-CAT NG) and the Planmeca ProMax 2D A SEDENTEXCT dose index adult phantom and custom-built adolescent and pediatric PMMA dosimetry phantoms were used Panoramic radiographs were performed using a Planmeca ProMax 2D and the panoramic mode on a Carestream 9300 CBCT and an i-CAT NG using the protocols used clinically Point dose measurements were performed at the center, around the periphery and on the surface of each phantom using a thimble ionization chamber Five repeat measurements were taken at each location For each machine, single-factor ANOVA was conducted to determine dose differences between protocols in each phantom, as well as determine the differences in absorbed dose when the same protocol was used for different-sized phantoms For any individual phantom, using protocols with lower kVp, mA, or acquisition times resulted in statistically significant dose savings, as expected When the same protocol was used for different-sized phantoms, the smaller phantom had a higher radiation dose due to less attenuation of x-rays by the smaller phantom and differences in the positioning of the ion chamber relative to the focal trough The panoramic-mode on the CBCT machines produce images suitable for clinical use with similar dose levels to the stand-alone panoramic device Significant dose savings may result by selecting age- and size- appropriate protocols for pediatric patients, but a wider range of protocols for children and adolescents may be beneficial PACS 87.53.-j, 87.57.-s, 87.59.-e, 87.53.Bn KEY WORDS paediatric dentistry, panoramic radiography, radiation dosimetry, radiographic phantoms, radiology | INTRODUCTION cone beam computed tomography (CBCT), manufacturers are including additional functionality including panoramic-imaging capabilities Panoramic radiography is a two-dimensional x-ray examination that to provide an all-in-one system for dental imaging In some cases, produces an image of the dental arches.1 Due to advances in dental the additional functionality includes a reconstructed panoramic -This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited © 2017 The Authors Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc on behalf of American Association of Physicists in Medicine J Appl Clin Med Phys 2017; xx: 1–9 wileyonlinelibrary.com/journal/jacmp | | WAHID ET AL image obtained from a CBCT dataset and reformatting within the examining the radiographic dose on pediatric patients from panora- software, which may remove some of the superposition of structures mic radiography, and none when using the panoramic-mode on a that are expected in the panoramic image Software reformatting CBCT unit A study conducted by Hayakawa et al examined the provides a series of useful images from a single acquisition (3D vol- doses in a dry-skull phantom representing a 5–6 yr old child for two umes, 2D slices through anatomy of interest, 2D panoramic view, single-function panoramic machines.10 Comparing adult and child etc.) but clinicians must remember that the dose for the 3D acquisi- imaging protocols for the phantom, Hayakawa et al concluded that tion is higher than for panoramic imaging2 and this technique should pediatric exposure settings reduce dose irrespective of machine only be done if the 3D images are required However, some CBCT Choi et al have developed two pediatric head-sized PMMA phan- machines also offer a panoramic acquisition to obtain a true 2D toms, representing a child aged yr and an adolescent aged 12 yr, image that is advertised as comparable with stand-alone machines, and measured the absorbed dose in various locations in dental with some manufacturers’ boasting a reduction in dose over stand- CBCT,11 leading to the same conclusions that pediatric exposure set- alone panoramic-imaging systems To date, no dosimetry studies tings could dramatically decrease patient doses have been reported in the scientific literature to compare the dose The aim of this study was to measure and compare the absorbed received by the patient or the dose distribution in combination units dose in adult, adolescent, and child head-sized PMMA phantoms for compared with single-function panoramic-imaging machines three panoramic-imaging devices: the panoramic modes on the Care- Panoramic machines often use pre-set imaging protocols with stream 9300 CBCT and i-CAT Next Generation CBCT, and the Plan- various exposure parameters (kVp, mA, acquisition time) that deter- meca ProMax 2D panoramic machine The study also aims to mine the radiation dose to a patient Helmrot et al have suggested establish the importance of selecting patient-appropriate protocols, using the dose area product (DAP) as a standardized dose metric for particularly in pediatric patients all dental radiography3 due to the convenience of measurements and that the DAP is measured independent of the patient and can therefore be specified by the manufacturer The DAP has been used to establish radiation output reference levels in Greece4 and Germany,5 although the reference levels are highly dependent on the measure- | METHODS AND MATERIALS 2.A | Phantoms ments used to find the 75% dose level, but are not for defining Cylindrical polymethyl methacrylate (PMMA) phantoms containing absorbed or effective doses Although the DAP values are obtained five holes drilled through the height of the cylinder for ionization at the tube port in an empty field, and therefore not including the chamber placement (Fig 1) were used to measure the dose The beam dispersion or scattering effects within the patient, they have adult phantom was the commercially available SEDENTEXCT DI been used to estimate the effective doses for patients using pub- (Leeds Test Objects, Ltd, York, UK) measuring 160 mm diameter lished conversion factors.3,5 However, the results are highly variable 162 mm height The adolescent and pediatric phantoms were depending on the measurement techniques and whether the salivary glands were included in the effective dose calculations;5 the tissue- (a) (b) (c) weighting factors were updated in ICRP 2007, which assigned a weighting factor to the salivary glands instead of including them in the remainder tissues.6 Roberts et al have also shown that effective doses calculated using older tissue-weighting factors (from 1990) for dental imaging are roughly half that using the factors published in 2007, six primarily due to the inclusion of the salivary glands in the calculation,7 which limits the applicability of effective dose measurements We propose using the absorbed dose measurement within a head-sized PMMA phantom, as it represents the energy absorbed within the phantoms, including dose from both the primary and scattered radiation, and can be used to estimate other metrics if desired Although dental imaging contributes less than 0.1% of the radiation dose the global population receives, radiation risk should always be considered when conducting panoramic radiography.2 The radiation risk is three times greater in patients that are less than 10 yr old compared to those that are above 30 yr.8 The increased radiosensitivity of tissues in children, along with their longer anticipated life span post-exposure, increases their risk of developing cancer over their lifetime.9 The radiosensitive nature of pediatric patients validates the need to carefully monitor the radiation exposure to these patients in particular There are very few studies F I G Comparison of different head-sized PMMA phantoms from top and side view (a) Adult 160 mm diameter 162 mm height, (b) Adolescent 135 mm diameter 150 mm height, (c) Child 100 mm diameter 150 mm height WAHID | ET AL designed in our lab and custom-built (British Columbia Cancer Agency, Genome Sciences Center, Vancouver, Canada) The adolescent phantom (135 mm diameter 150 mm height) was designed to represent a 12-year-old child beginning orthodontic treatment, T A B L E Comparison of panoramic-imaging protocols for Carestream 9300 and i-CAT NG combination machines with the Planmeca ProMax 2D stand-alone machine Image sizes (width x height) are included for the average adult setting whereas the child phantom (100 mm diameter 150 mm height) 11 was designed to represent a 5-year-old child The dimensions of the custom-built phantoms were obtained from measuring anatomic reference points in the dental CBCT images of pediatric patients Protocol Time (s) kVp Tube current (mA) DAP (mGycm2) Phantoms Carestream 9300 (260 149 mm) Child 13.2 64 Small adult 13.6 68 Average adult 14.3 70 10 104 Adult, DXXTR natural bone skull embedded in resin The head has detailed facial Large adult 15.3 74 10 130 Adult features to enable positioning using anatomical landmarks and is i-CAT NG (316 153 mm) mounted on a tripod that can articulate to enable angling the head Small 18.3 84 91 Adolescent, child to align with the laser positioning guides Large 20 94 146.4 Adult, adolescent, DXXTR A panoramic radiograph of a Pan DXTTR (Rinn Corporation, Elgin IL, USA) was taken by each machine to assess their images The DXTTR phantom is an anthropomorphic phantom comprised of a 2.B | Imaging systems 10 58.6 72.4 Adolescent, child Adult, adolescent Planmeca promax 2D (233 114 mm) Small child (