Diagnostic performance and organ dose evaluation in radiological diagnosis and follow-up of Ollier enchondromatosis pediatric patients: a phantom study

The European Council Directive 2013/59/Euratom included pediatric exposure in the special practices for which appropriate medical radiological equipment and practical techniques have to be ensured. Children are generally more sensitive to X-rays than adults, mainly due to rapid cell growth and replication, and a longer lifespan after exposure. Hence, the optimization of protection is a priority factor and it shall involve all the practical aspects of medical radiological procedures, from the selection of equipment to quality assurance and the assessment of patient doses. These concepts are strongly endorsed by health care organizations dedicated to providing safe and high-quality pediatric imaging, particularly in modalities involving higher radiation doses, such as computed tomography and fluoroscopy. IRCCS Istituto Ortopedico Galeazzi is a reference center for the diagnosis and treatment of pediatric orthopedic and traumatological diseases, including orthopedic tumors. Ollier disease is a rare skeletal disorder characterized by the presence of multiple enchondromas, which are intraosseous, usually benign, cartilage tumors. Although the enchondromas start out as benign, they may become malignant, so children affected by the disease undergo multiple radiographs over time. Special effort is thus required to reduce the risk of radiation-induced cancers, and the benefit provided by radiological procedures has to be properly balanced with the health risk associated with ionizing radiation. The principal aim of this study was to evaluate the applicability of a relatively novel low-dose technique based on a slot scanning technology (EOS imaging system), for the diagnosis and follow-up of Ollier disease. For this purpose, a 5-year-old anthropomorphic phantom was specifically purchased to evaluate the diagnostic and dosimetric performances of the system. Digital radiography (DR) and computed tomography (CT), the current gold standards for diagnosis and monitoring, were evaluated for comparison. Ollier enchondromas were simulated with homemade bone structures stuck on the phantom, which was then imaged with DR, CT, and the EOS system at three different scanning speeds. To assess the diagnostic power of the imaging system, non-expert observers and experienced radiologists measured the inserts dimensions and compared them with those derived from CT and DR. Interobserver and intermodality reproducibilities were evaluated through Bland-Altman analysis. Furthermore, the accuracy in the size estimation was investigated by comparing the measured dimensions with the real ones. Dosimetric evaluations were performed for each imaging technique through Monte Carlo (MC) simulations and in-phantom measurements with thermoluminescent dosimeters (TLDs). The validation of MC simulations with TL dosimetry was necessary for the EOS system as no reference was found in the literature. Three speed levels of the EOS X-ray tube, and two DR acquisition protocols, respectively suited for diagnosis and follow-up, were investigated. The measured organ doses were used to calculate effective dose according to the ICRP 103 recommendations. Risks of radiation-induced cancers were estimated in the form of Lifetime Attributable Risk (LAR). The EOS system performed similarly to DR and CT in both detection and measurement of enchondromas-like inserts. Excellent intermodality reliability and interobserver reproducibility were obtained for each imaging technique. EOS fast protocol provided a reduction of effective and organ doses with respect to DR acquisitions performed with the diagnostic protocol. When the DR protocol optimized for follow-up was considered, instead, no significant dose sparing was observed, neither in organ doses nor in effective dose. CT doses were considerably higher than doses of EOS and DR, regardless of the acquisition protocol or speed level. Comparable LARs were observed for EOS acquisitions performed with the fast protocol and DR examinations with the follow-up protocol. DR diagnosis protocol was found to be equivalent, in terms of radiological risk, to the EOS intermediate speed level. The risk associated with CT examinations was two orders of magnitude higher than of the other techniques. This work showed that the EOS system has the same diagnostic capability as DR and CT to detect and measure enchondromas-like inserts in a pediatric phantom, but delivering lower doses. Although no dose reduction was found with respect to DR follow-up protocol, EOS fast protocol still provides low doses, and the two techniques were found to be equivalent in terms of LAR. Thus, it may be considered a valid solution for both the diagnosis and followup of patients with Ollier disease or other bone pathologies, allowing easier and faster exams, which is a crucial aspect in pediatric applications.