| Περίληψη: | In recent years, an increasing number of fluoroscopically guided procedures has been introduced into the field of spine surgery. However, the use of fluoroscopy by neurosurgeons outside the imaging department, where in most cases lacking of appropriate training and awareness in radiological protection issues, resulting in increased radiation risks to both patients and medical staff. Thus, patient and staff dose monitoring, its optimization, as well as the implementation of a quality assurance programme becomes essential for all spine interventional procedures.
In the framework of this thesis, an evaluation and optimization of patient dose and image quality in fluoroscopically guided cervical discectomy and fusion procedures is performed. The patient’s dose evaluated utilizing the dosimetric quantities recorded from the dosimetric report of the fluoroscopy system (fluoroscopy time, kerma-area-product (KAP), cumulative dose (CD)), while the correlation of the KAP and CD values with fluoroscopy time is also studied. The KAP values, the exposure parameters (tube voltage, tube current, tube output), as well as irradiation geometry parameters (projection, field size, focus-to-detector distance, focus-to-skin-distance) were used as ‘‘input’’ in CALDoseX 5.0 software, based on Monte Carlo simulation, to estimate the patient entrance surface dose (ESD), effective dose (ED) and thyroid absorbed dose. As part of this thesis, conversion coefficients were also estimated based on KAP values, in order to estimate mean organ absorbed doses during such procedures. The factors taken into consideration in dose assessment are the patient’s gender and body mass index, the type of fusion (single or multiple levels), the surgical approach, as well as neurosurgeon experience. In addition, comparison of the results with corresponding dosimetric studies from the literature is carried out.
In order to optimize the procedure, both in terms of patient dose and image quality, an experimental study is carried out utilizing a PMMA phantom and the TOR 18FG test object to simulate the patient, under clinical exposure conditions. The effect of all the parameters selected by the operator of the fluoroscopy system (fluoroscopy mode: continuous or pulsed, low or high dose fluoroscopy, electronic or geometric magnification), as well as the patient’s size is studied, in terms of ESD to the patient and image intensifier. The corresponding images obtained from all irradiation combinations were subjectively evaluated by observers in terms of detectability and discriminability of specific low-contrast and high-contrast objects respectively, as well as utilizing physical image quality metrics (signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), high-contrast spatial resolution (HCSR)). A figure of merit (FOM) was also introduced, combining the dosimetric and imaging performance of the fluoroscopy system, in order to select the optimal settings of the fluoroscopy system with respect to patients’ size to be treated. Additionally, a series of practical guidance is provided towards further optimization of the radiological protection during these procedures.
Furthermore, within the framework of the development and implementation of a quality assurance and radiation protection programme for neurosurgical procedures in spine, local diagnostic reference levels (LDRLs) and action levels (ALs) are estimated for cervical discectomy and fusion, as well as for thoraco-lumbar discectomy and fusion procedures. A preliminary evaluation for ESD, ED and gonadal dose received by the patients undergoing interventions in thoracic and/or lumbar spine was also performed, using appropriate conversion coefficients based on KAP values. The reference levels were calculated as the 75th and 10th percentile respectively, for fluoroscopy time, KAP and CD values utilizing three methods (for the total sample of patients, with size correction method and weight banding method) and compared between them and with corresponding values from the literature. The distribution histograms of KAP and CD values were also studied and the dose values were correlated with fluoroscopy time. The influence of several anatomical, clinical and technical factors affecting procedure complexity, on the reference dose values was investigated. The factors investigated are the patient’s age and gender, the body mass index, the type of fusion (single or multiple levels), the surgical approach and treated levels, the type of implants (cages and/or rod, screws), as well as the neurosurgeon experience.
Finaly, the limitations of this thesis are reported and topics for future work are proposed that could further contribute towards awareness, training and establishment of radiation protection culture by the neurosurgeons and all those involved in minimally invasive spine surgery.
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