| Περίληψη: | Endoscopic retrograde cholangiopancreatography (ERCP) is an interventional procedure (IP) performed for the diagnosis and treatment of hepatobiliary diseases. During the performance of ERCP, fluoroscopy is used in order to verify the right placement of the catheter and to evaluate the anatomy of the ductal systems, after injection of the radiopaque contrast media. Fluoroscopy is also needed to assist in the therapeutic procedures, such as sphincterotomy, stone extraction, bile duct dilatation or stent placement. However, X - ray radiation, associated with fluoroscopy, exposes patients and staff to high doses, due to the long fluoroscopy time (FT) required, leading to radiation-induced skin injuries. This is mainly related to the complexity of the procedure and its performance outside the radiological department by operators of questionable knowledge and training on radiation protection issues. This, in combination with a great variability, reported in previous studies, suggests the need for further investigation and therefore highlighting the great importance for optimisation of these procedures.
Optimisation is interpreted by keeping the patient dose as low as possible, which is consistent with the required image quality (IQ) and necessary for obtaining the desired diagnostic information. Equipment features, that allow this to be accomplished, and diagnostic reference levels (DRLs) derived at national, regional or local level are likely to be the most effective approaches, as recommended by the international organisations. However, available information regarding DRLs for ERCP is quite limited. Currently, there are no existing national DRLs for ERCP in Greece. Another tool to achieve optimisation in X - ray imaging procedures is the use of appropriate phantoms, which allow an objective evaluation to reach the optimum balance between patient dose and IQ. Such studies have been reported in various IPs, mainly in cardiology whilst in ERCP procedures have not been reported.
The framework of this thesis was to investigate the current level of patient radiation doses in the University Hospital of Patras and to determine the association of operator experience on FT and patient radiation dose, as well as to achieve optimisation of radiation protection during the therapeutic ERCP procedures. Thus, this thesis was divided into two studies, the patient study and the phantom - based study. The patient study was aimed at measuring the radiation dose to patients during therapeutic ERCP, in order to estimate the patient effective dose (ED), utilising the air kerma-area product (PKA) measurements, and to compare them with the corresponding values previously reported to assess the current level of patient radiation doses in the University Hospital of Patras, utilising a fluoroscopy system equipped with a flat panel (FP) detector (Part A). In addition, it was aimed to obtain the institutional DRLs, to compare them with the results of previous studies (Part B) and to assess the key role of the operator (Part C), utilising FT, cumulative dose (Ka,r) and PKA. The values obtained could contribute in establishing local and national DRLs. The phantom - based study was aimed to optimise the patient dose and IQ in ERCP procedures. The influence of the patient thickness, geometric characteristics and X - ray system settings on both patient dose and IQ is investigated. The evaluation is based on a phantom utilising a test object (TO).
The same fluoroscopy system was utilised for the patient and phantom studies, which was equipped with a FP detector, automatic brightness control, last image hold and pulse fluoroscopy mode. For the investigation of the current level of patient radiation doses fifteen patients were studied and the dosemetric indices FT, Ka,r and PKA were collected. The patient ED was calculated by multiplying each PKA value with the appropriate conversion coefficient. The correlation between FT and Ka,r as well as between FT and PKA was also investigated, using the Pearson test. For the establishment of institutional DRLs for the therapeutic ERCP procedure, ninety-six patients participated in the study. The dosemetric indices, FT, Ka,r and PKA, were collected and the third-quartile method was adopted. For the total group of patients, the weight banding method was utilised to reduce the variability of the dosemetric data, due to patient weight variation. The total group of patients was also divided into three groups, based on the operator experience to assess the key role of the operator on FT and patient radiation doses, utilising FT, Ka,r and PKA.
In the phantom study, the patient thickness was simulated with various polymethyl methacrylate slabs, whilst IQ was evaluated utilising the Leeds TO. The main factors evaluated were phantom thickness, distance between phantom and detector, field of view and pulse rate. For all these factors, the dosemetric indices phantom incident air kerma rate (K ̇_(a,i)) and phantom incident air kerma per pulse, as well as the IQ parameters, signal to noise ratio and high contrast spatial resolution, were measured. Based on these measurements, the figure of merit (FOM) was estimated. The FOM and K ̇_(a,i) values indicates the optimum combination of the factors evaluated which could provide adequate clinical information, assuring minimum patient dose.
Regarding the results of the Part (A), the FT ranged from 0.68 to 5.57 min, with a mean value of 2.50 min; the Ka,r ranged from 2.22 to 19.10 mGy, with a mean value of 7.71 mGy; and the PKA ranged between 0.59 and 5.10 Gycm2, with a mean value of 2.03 Gycm2. The ED ranged from 0.11 to 0.97 mSv, whilst the mean and median ED values were 0.39 and 0.32 mSv, respectively. FT and radiation dose to the patients were either comparative or significantly lower than those previously reported. In the part (B), the mean FT was 2.18 min and ranged between 0.58 and 5.72 min, the mean Ka,r was 4.94 mGy and ranged between 1.34 and 12.60 mGy and the mean PKA was 1.31 Gycm2 and ranged between 0.36 and 3.38 Gycm2. For the total and weight banding group the third quartile values of the distribution of FT, Ka,r and PKA were 2.90 and 2.92 min, 6.89 and 6.93 mGy and 1.84 and 1.85 Gycm2, respectively and were comparative or significantly lower than the corresponding values previously reported. Taking as a criterion the operator (Part C), the differences in the patient radiation doses were statistically significant, with the highest dose recorded for the operator with the lowest degree of experience. The operator with the highest degree of experience resulted in lower mean FT, Ka,r and PKA values.
The phantom based study performed provided FOM and K ̇_(a,i) rate values indicating the optimum combination of distance between patient and detector, FOV and pulse rate resulting to minimum patient dose and adequate clinical information, during ERCP procedures. Specifically, the optimum combination was the minimum distance between the patient and the detector, the maximum FOV and the lowest pulse rate.
In conclusion, regarding the patient radiation doses and institutional DRLs the values obtained were either comparative or significantly lower than those previously reported. The values obtained can contribute in establishing local and national diagnostic reference levels and in optimising the ERCP procedure. Regarding the operator, the higher operator experience, in combination with the increased awareness, resulted in a lower mean patient radiation dose, therefore highlighting the key role of the operator towards optimisation of the ERCP procedure and the radiation protection of the patient. However, further investigation including the complexity of the procedure, a larger number of patients and fluoroscopy systems and a larger number of operators with various degrees of experience could contribute to more reliable results towards the optimisation of the ERCP procedure.
Simultaneously, the phantom based study performed indicated the optimum values of distance between patient and detector, FOV and pulse rate, which could provide adequate clinical information, assuring minimum patient radiation dose. However, these measures should be further evaluated in clinical practice by gastroenterologists, in collaboration with medical physicists. In general, the phantom based studies could contribute in providing critical information towards the optimisation management of patient radiation protection and IQ in IPs.
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